Deep Water research

Boiling point of water and atmospheric pressure

What is the boiling point of water at sea level in Celsius?

Sep 26, 202616 sources reviewed

Key Takeaways

Ordinary water boils around 100°C at sea-level pressure. [3][4][5]

  • Answer: Water boils when vapor pressure matches surrounding pressure; at sea-level 1 atm (101.325 kPa) ordinary water reaches 100°C (212°F). [3][4][5] Precise value sits near 99.97°C at 101.325 kPa. [4][8][12] Handbook pins normal point to 101.325 kPa. [1][4][8] One report suggests heavy water boils near 101.42°C at 101.325 kPa. [1]
  • Tradeoff: Pressure basis controls the figure; water under IUPAC 1-bar standard (100 kPa) boils near 99.61°C, below the 101.325 kPa normal point. [4][8][12]
  • Risk: Climbing lowers boiling sharply, with Denver water boiling near 95°C below sea-level 100°C. [7][10][3] One report suggests dissolved non-volatile salts lift it proportionally. [4]
  • Caveat: Evidence suggests actual sea-level pressure varies with location and weather, with one report suggesting ±0.2–0.5°C boiling shifts. [12][10] One report suggests a −0.026°C ITS-90-minus-IPTS-68 gap at 100°C. [2]

[!WARNING]

Taken together, [4][8][7] indicate using 100°C away from 101.325 kPa misleads, from IUPAC 1-bar water near 99.61°C to Denver near 95°C.

Abstract

Taken together, [4] and [8] indicate water boils at 100 °C, rounded from scientific precision of 99.97 °C under standard pressure at sea level [4]. The normal boiling point of water is given as 99.97 degrees Celsius at 1 atm (i.e., 101.325 kPa) [8], above the 99.61 °C standard boiling point at 100 kPa (1 bar) [4][8].

  • The boiling point is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid [4] and the environmental pressure surrounding the liquid [8].
  • Boiling occurs when the vapor pressure exerted by water equals atmospheric pressure [7].
  • At higher elevations, where the atmospheric pressure is much lower, the boiling point is also lower [4][8]. At higher altitudes where atmospheric pressure is lower, water boils at a lower temperature [3].
  • The boiling point increases with increased pressure up to the critical point [8], including in a pressure cooker where increased pressure raises the boiling point above 100 °C [3].
  • The CRC Handbook defines the normal boiling point as the boiling point at normal atmospheric pressure (101.325 kPa) [1] and tabulates water at 100.0 °C [1].
  • The standard boiling point is given as 100 °C (212 °F) at sea-level atmospheric pressure (1 atm or 101.325 kPa) [3]. Water boils at 212 degrees Fahrenheit or 100 degrees Celsius at sea level [5].
  • The tabulated difference between ITS-90 and IPTS-68 at t90 100 °C is -0.026 °C [2]. CoolProp gives 99.9743 °C at 1 atmosphere (101325 Pa) [12].
  • In the Denver area water boils at about 95 degrees C [7].
  • Taken together, [4][7][8] indicate Everest reports span 69 °C where pressure is about 260 mbar (26.39 kPa) [8] to about 72 degrees C where pressure is about 34% of sea level [7], including 71 °C at about 34 kPa at 8,848 m elevation [4].
  • The presence of non-volatile impurities such as salts raises the normal boiling point in proportion to the concentration of the solutes [4].
  • The actual pressure of the atmosphere at sea-level varies above and below that according to location and countless weather influences [12]. Real weather can shift pressure a bit, changing Tb by ~±0.2–0.5 °C [10].
  • In Death Valley at 282 feet below sea level water boils at slightly above 212 degrees [11].

Table of Contents

  • Key Takeaways
  • Abstract
  • 1. Introduction
  • 2. Background
  • 3. Findings
    • 3.1 Water Boiling Point Values at Standard Pressures
    • 3.2 Altitude, Pressure, and Impurity Effects on Boiling
    • 3.3 Water Boiling Point Values Across Temperature Scales and Pressures
  • 4. Discussion
  • 5. Conclusion
  • References

1. Introduction

This report asks what temperature boils water at sea level in Celsius. See Background for boiling and sea-level reference definitions, and Findings for pressure effects and purification timings. The boiling point does not depend on the amount of the material and remains constant for a given substance under specific conditions such as pressure, one report suggests [3].

Taken together, [7][9][11] and [4][7][8] indicate altitude affects pressure and boiling.

This investigation covers pure liquid water at sea-level pressure, reported in Celsius. Scope stays tight.

  • It deliberately excludes dissolved salts, isotopic variants, and altitude-adjusted cooking tables except as background.
  • Calibration and superheating stay out.
  • Comparisons use Celsius throughout.

Background defines boiling and the sea-level reference. In Findings, pressure definitions and temperature scales frame the sea-level value. Discussion tests those definitions against practical limits.

Structure follows four steps. Conclusion answers the research question and notes remaining uncertainties. No new measurements appear here.

2. Background

Boiling marks the temperature where vapor pressure matches surrounding pressure and liquid turns to vapor [4][8]. The normal boiling point fixes that match at defined sea-level atmospheric pressure, one atmosphere [1][4][8]. Normal atmospheric pressure sits at 101.325 kPa [1][3]. Evidence suggests IUPAC defines standard boiling point at 1 bar since 1982 [4][8]. Keep that distinction in mind.

One report suggests the boiling point does not depend on the amount of the material and remains constant for a given substance under specific conditions such as pressure [3].

t/°C = T/K − 273.15 [2]. The International Temperature Scale of 1990 was adopted by the International Committee of Weights and Measures at its meeting in 1989, in accordance with the request embodied in Resolution 7 of the 18th General Conference of Weights and Measures of 1987 [2]. This scale supersedes the International Practical Temperature Scale of 1968 (amended edition of 1975) and the 1976 Provisional 0,5 K to 30 K Temperature Scale [2].

One report suggests the Celsius temperature scale was defined until 1954 by two points: 0 °C being defined by the water freezing point and 100 °C being defined by the water boiling point at standard atmospheric pressure [4].

3. Findings

3.1 Water Boiling Point Values at Standard Pressures

Ordinary water boils at 100 °C when sea-level pressure holds at 1 atm, Vaia chemistry material reports [3]. The handbook defines 1 standard atmosphere as 101.325 kPa [1] and lists the same unit as 1.01325 × 10^5 Pa [1]. Webel defines one atmosphere as exactly 101,325 Pa [12]. Section 2 traces full standards provenance.

NIST gives t/°C = T/K − 273,15 with degree Celsius equal in magnitude to the kelvin [2]. The handbook states T0 = 273.15 K by definition, noting that the thermodynamic temperature T0 is exactly 0.01 K below the thermodynamic temperature of the triple point of water [1].

See Section 2 for boiling and normal-point definitions. The handbook lists Tb in kelvins [1]. Vaia chemistry material defines the standard boiling point as the temperature at which a substance transitions from a liquid to a vapor under a pressure of 1 atmosphere [3]. Wikidoc equates saturation temperature with boiling point for corresponding saturation pressure [8]. Section 2 owns primary-standards detail.

Handbook tables pin ordinary water at 100.0 °C in UV-solvents (tb) and laboratory-solvents listings [1]. 100.00 °C at 1013.25 mbar appears in handbook pressure table [1]. Δt/Δp 0.276 °C/kPa (0.0368 °C/mmHg) at tb 100.0 °C appears in that handbook listing [1]. Melting stays out of scope. The laboratory-solvents entry pairs 0.00 °C melting with boiling [1] and a separate handbook entry gives H2O melting tm 0.00 °C with 6.01 kJ/mol fusion enthalpy [1]. Section 1 details pressure sensitivity.

Everyday sea-level summaries repeat 100 °C (212 °F), EBSCO and Wikipedia listings show [5][6].

  • Approximately 100 degrees Celsius marks sea-level boiling, MadSci archive gives [7].
  • The standard boiling point is 100 °C at sea-level atmospheric pressure, Vaia chemistry material states [3], and typically 100 °C where pressure is about 101.325 kPa, the same Vaia material describes [3].
  • 212 °F marks sea-level boiling, Mountain House material reports [9].
  • Pew Research material states "Water boils at 212 degrees Fahrenheit (100 degrees Celsius), right?" [11].
  • 100 °C (212 °F) repeats at sea level in Wikipedia high-altitude-cooking material [6].
  • Altitude shifts live in Section 1.

The familiar 100 °C is rounded from 99.97 °C, Wikipedia accounting shows [4].

  • Actually 99.97 °C (211.9 °F) holds at 1 atm (101.325 kPa), Wikipedia gives [4].
  • 99.97 degrees Celsius for purists marks 1 atm (101.325 kPa), Wikidoc states [8].
  • 99.9743 °C at 101325 Pa comes from CoolProp calculation, Webel reports [12].
  • Precision lives in Section 2.

Salt water boils at a higher temperature than pure water [4].

Substance Boiling point at 101.325 kPa on the IPTS-68 scale [1]
H2O 100.00 °C [1]
D2O 101.42 °C [1]

Atmospheric pressure is defined to be exactly 101,325 Pa [12]. The actual 'pressure of the atmosphere' at sea-level varies above and below that according to location and countless weather influences [12]. Taken together, [12] and [12] indicate actual sea-level pressure varies above and below 101,325 Pa.

The specific volume of water at standard atmospheric pressure is given as a function of temperature [1].

Altitude and pressure shift boiling.

  • Atop Mount Everest, boiling is at about 72 degrees C [7].
  • At h ≈ 1609 m, P ≈ 83.3 kPa and Antoine inversion gives T ≈ 94.6 °C [10].
  • P = 90 kPa → 675 mmHg with Antoine inversion giving T ≈ 96.7 °C [10].
  • At 5,000 feet above sea level, the boiling point is 203 degrees F [9].
  • The Centers for Disease Control & Prevention recommends letting water stand at a rolling boil for a minute at sea level to purify it and extending that to three minutes of a rolling boil above about 6,500 feet [9].
  • Section 1 owns shift detail.

Estimation uses standard atmosphere and vapor-pressure relations.

  • Pearson material gives the water Antoine equation as log10 P(mmHg) = 8.07131 − 1730.63/(233.426 + T(°C)) for 1–100 °C [10].
  • Water's Antoine constants are standard and accurate in 1–100 °C [10].
  • For other liquids, reliable constants vary and Clausius–Clapeyron with ΔHvap is used [10].
  • In water mode the boiling temperature is obtained by inverting the Antoine equation for pressure [10].
  • Altitude h is converted to pressure with the standard atmosphere (0–11 km) [10].
  • The Clausius–Clapeyron relation ln(P2/P1) = −ΔHvap/R (1/T2 − 1/T1) with P1 = 1 atm at the normal boiling point T1 is solved for T2 at ambient P2 [10].
  • Section 1 owns method detail.

3.2 Altitude, Pressure, and Impurity Effects on Boiling

The boiling point of water, or any liquid, varies according to the surrounding atmospheric pressure [11].

Altitude lowers air pressure, as recorded by the MadSci Network archive [7]. Mountain House reports the same decrease with increasing altitude [9]. Pew Research explains pressure drops gaining elevation from Los Angeles to Denver because fewer air molecules press down [11].

Lower pressure gives lower, faster boiling.

  • Lower pressure lets water boil cooler, according to the MadSci Network archive [7].
  • Vaia textbook materials place mountain boiling below 100 °C [3].
  • Wikipedia and Wikidoc report lower boiling at higher elevations where atmospheric pressure is much lower [4][8].
  • Higher altitudes with lower pressure give lower boiling temperature, Vaia textbook materials also note [3].
  • Water reaches its boiling point faster at higher altitudes because lower pressure reduces needed temperature, Mountain House reports [9].

Water will boil at about 202 degrees in Denver, due to the lower air pressure at such high elevations [11]. In Denver, the atmospheric pressure is only about 12 pounds per square inch, compared with 14.7 pounds per square inch in Los Angeles [11]. With that much less pressure, you don't need to apply as much heat to push vapor pressure beyond the surrounding atmospheric pressure [11].

Mid-elevation pressure and boiling observations.

Site / elevation Atmospheric pressure Reported boiling point
Los Angeles, close to sea level [11] 14.7 pounds per square inch [11] —
Denver [11] about 12 pounds per square inch [11] about 202 degrees [11]
Denver area [7] about 83% of sea-level pressure [7] about 95 degrees C [7]
1,905 metres (6,250 ft) [4] — 93.4 °C (200.1 °F) [4]
10,000 feet [9] — 194 degrees F [9]

Differing sources give different Everest pressure-temperature pairs.

  • 71 °C (160 °F) boils water atop Everest, according to Wikipedia [4]. That summit is 8,848 m (29,029 ft) [4]. Pressure there is about 34 kPa (255 Torr), Wikipedia places [4].
  • At the peak of Mount Everest (29,029 feet), water boils at about 162 degrees for tea, Pew Research puts [11].
  • On top of Mount Everest the pressure is about 260 mbar (26.39 kPa) so the boiling point of water is 69 °C (156.2 °F), Wikidoc lists [8].
  • Atop Mount Everest, it is about 34% of sea level, the MadSci Network archive states [7].
  • Taken together, [4] and [8] indicate these are differing source-specific pressure-temperature pairs, not one agreed value.

Added pressure lifts boiling, according to Wikidoc [8]. Death Valley boiling is slightly above 212 degrees, Pew Research places [11]. That site sits 282 feet below sea level as the lowest U.S. point in California, Pew Research locates [11]. A pressure cooker increases pressure to raise boiling above 100 °C and cook food faster, Vaia textbook materials state [3]. The rise continues up to the critical point where gas and liquid properties become identical, Wikidoc states [8].

Wikipedia notes the presence of non-volatile impurities such as salts decreases its mole fraction and the solution's volatility [4].

You can get a rough estimate of the boiling point change by subtracting about one degree Fahrenheit from the boiling temperature with each 500-foot increase in elevation [9]. Weather-related shifts and direct pressure entry are covered elsewhere in this section [10].

Hydrogen bonds within water molecules and their interactions determine the boiling point, according to Vaia textbook materials [3]. Water stays high versus similar-sized methane or oxygen, Vaia notes [3].

According to Mountain House, that can affect how long water comes to a boil by whipping that gas flame around and otherwise making it harder to heat your pot [9]. Many experts contend that simply allowing water to reach a rolling boil renders it safe, regardless of your elevation [9].

3.3 Water Boiling Point Values Across Temperature Scales and Pressures

The CRC Handbook defines boiling point as the temperature at which the liquid and gas phases of a substance are in equilibrium at a specified pressure [1]. Boiling points may be published with respect to the NIST, USA standard pressure of 101.325 kPa (1 atm), or the IUPAC standard pressure of 100.000 kPa (1 bar), according to Wikipedia's boiling-point entry [4]. Wikipedia's boiling-point entry and Wikidoc state that the standard boiling point has been defined by IUPAC since 1982 as the temperature at which boiling occurs under a pressure of one bar [4][8].

The IUPAC-recommended standard boiling point of water at a standard pressure of 100 kPa (1 bar) is 99.61 °C [4], reported at this slightly reduced pressure as 99.61 degrees Celsius [8]. At 100,000 Pa, CoolProp gives a standard boiling point for water of 99.6059 °C [12].

Comparison of normal and IUPAC standard boiling points.

Basis Pressure Listed temperature
Normal boiling point [1] 101.325 kPa [1] 100.0°C [1]
Standard boiling point [4] 100.000 kPa (1 bar) [4] 99.61°C [4]

NIST's ITS-90 text and the CRC Handbook define the kelvin as the fraction 1/273.16 of the thermodynamic temperature of the triple point of water [2][1]. That point appears at 273,16 K and 0,01 °C in NIST's defining-fixed-point table, matching the Handbook's H2O triple-point entry at 273.16 K and 0.01 °C [2][1].

  • NIST's text determines temperatures in terms of the ratio W(T90) as R(T90) divided by R(273,16 K) at the triple point of water [2].
  • International Kelvin T90 and International Celsius t90 follow t90/°C = T90/K − 273,15, according to NIST's ITS-90 text [2].
  • A difference of temperature may be expressed in kelvins or degrees Celsius, according to NIST's ITS-90 text [2].
  • After 2007 it was defined to be based on Vienna Standard Mean Ocean Water (VSMOW), a precisely defined water standard, according to Webel's note [12].
  • In 2019 the definition of the kelvin scale (and resulting impact on the Celsius scale) was changed to be based on the Boltzmann constant, rather than depending on the solid-liquid-gas triple point of water, according to Webel's scale note [12].

ITS-90 adoption, range and definition provisions.

  • Measurements of T90 are described as more easily made, more precise and highly reproducible by comparison with direct measurements of thermodynamic temperatures [2].
  • Adoption came in 1989 by the International Committee of Weights and Measures at its meeting in 1989, in accordance with the request embodied in Resolution 7 of the 18th General Conference of Weights and Measures of 1987, according to NIST's ITS-90 text [2].
  • Supersession replaced the International Practical Temperature Scale of 1968 (amended edition of 1975) and the 1976 Provisional 0.5 K to 30 K Temperature Scale, NIST's ITS-90 text states [2].
  • The scale extends upwards from 0.65 K to the highest temperature practicably measurable in terms of the Planck radiation law using monochromatic radiation, NIST's ITS-90 text defines [2].
  • Webel's note states that the International Temperature "Scale" of 1990 is not a scale but an equipment calibration standard [12].
  • Between the triple point of equilibrium hydrogen (13.8033 K) and the freezing point of silver (961.78°C) T90 is defined by means of platinum resistance thermometers calibrated at specified sets of defining fixed points, according to NIST's ITS-90 text [2].
  • NIST's ITS-90 text sets p0 101325 Pa as the reference pressure for melting and freezing points, with the pressure effect for triple points as a consequence only of the hydrostatic head of liquid in the cell [2].
  • Throughout its range, for any given temperature the numerical value of T90 is a close approximation to the numerical value of T according to best estimates at the time the scale was adopted, and measurements of T90 are more easily made, more precise and highly reproducible by comparison with direct measurements of thermodynamic temperatures, according to NIST's ITS-90 text [2].
  • Where overlapping of ranges or sub-ranges occurs, differing definitions of T90 exist with equal status, with differences of negligible practical importance in virtually all cases, according to NIST's ITS-90 text [2].

Scale offsets and steam-table basis near 100 °C.

  • At t90 100°C the tabulated (t90-t68)/°C difference between ITS-90 and IPTS-68 is −0.026°C [2].
  • The freezing point of tin (231.9681 °C) became a permitted alternative to the boiling point of water [2].
  • The freezing point of zinc, defined as being 419.505 °C, became a preferred alternative to the sulphur boiling point (444.6 °C) as a calibration point [2].
  • Data are based on the equation of state recommended by the International Association for the Properties of Steam in 1984, as presented in Haar, Gallagher, and Kell, NBS-NRC Steam Tables (Hemisphere Publishing Corp., New York, 1984), and the temperature scale is IPTS-68 [1].
  • The listing gives "Water Boiling point 373.124 99.974 0.001" [1].

The enthalpy (heat) of vaporization of water is tabulated as a function of temperature on the IPTS-68 scale, listing 40.657 kJ/mol at 100°C [1]. The permittivity of saturated water vapor is listed as 1.00587 at 100°C [1]. The properties of water in the range 0 — 100 °C state that all values (except vapor pressure) refer to a pressure of 100 kPa (1 bar) and the temperature scale is IPTS-68, listing 0.95840 in the 100 entry [1].

Sample details live elsewhere. Sample-size independence and pressure-driven shifts with estimation methods stay with companion sections.

4. Discussion

The boiling definitions, everyday sea-level summaries, and precise and tabular values relevant here are detailed in Background and Findings; this discussion relies on those sections without restating them here.

See Background for the boiling definition [4][9][11], the Introduction for altitude–pressure context [9][11], Findings for the Everest comparisons [4][7][8], and Findings for the calculation method including pressure handling [10].

Boiling points may be published with respect to different standard pressures [4].

Everest pressure-temperature pairs differ by source.

  • On top of Mount Everest, at 8,848 m elevation, the pressure is about 34 kPa and the boiling point of water is 71 °C [4],
  • while Wikidoc reports about 260 mbar (26.39 kPa) and 69 °C [8],
  • and MadSci states atop Mount Everest it is about 34% of sea level, which translates into boiling at about 72 degrees C [7].
  • Taken together, [4][7] and [8] indicate different reported Everest pressure–temperature pairings.

5. Conclusion

Ordinary water hits 100°C — measured at 99.97°C — under one atmosphere (101.325 kPa), matching CRC Handbook tables and CoolProp calculations reported by Webel [1][4][12].

This is not the 99.61°C fixed for IUPAC's 1-bar standard [4][8][12], with altitude dropping that figure [4][7][9] and salt lifting the point in one report [4].

reader scenario recommended choice deciding factor
Sea-level water [3] Taken together, [1] and [4] indicate 100°C (99.97°C) at 101.325 kPa [1][4] Normal boiling point is at 101.325 kPa [1][4]
IUPAC 1-bar reporting [4][8] Taken together, [4] and [8] indicate 99.61°C at 100 kPa [4][8] IUPAC defines standard boiling point since 1982 as boiling under 1 bar [4][8]
High-altitude work [7][11] Taken together, [7] and [11] indicate lower boil [7][11]; if local pressure is known, entering it directly overrides altitude-derived pressure [10] Atmospheric pressure decreases with altitude [7][11]; lower pressure allows boil at lower temperatures [7][11]
Salted water [4] Taken together, [4] indicates higher boil [4] Non-volatile impurities such as salts raise normal boiling point in proportion to concentration [4]

Water is listed as 100°C at 101.325 kPa [1][3][4].

  • Water boils at 100°C, rounded from scientific precision of 99.97°C, under standard pressure at sea level [4], with the normal boiling point given as 99.97 degrees Celsius at 1 atm (i.e., 101.325 kPa) [8] and CoolProp giving 99.9743°C at 1 atmosphere (101325 Pa) [12].
  • The boiling point is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid [4] at a specified pressure [1].
  • Salt water boils at a higher temperature than pure water [4], with non-volatile impurities such as salts raising the normal boiling point in proportion to the concentration of the solutes [4].

Taken together, [4] and [8] indicate that work reporting against the IUPAC standard uses the IUPAC-recommended standard boiling point of water at 100 kPa (1 bar) of 99.61°C [4][8], because the standard boiling point has been defined by IUPAC since 1982 as the temperature at which boiling occurs under a pressure of one bar [4][8].

Boiling points may be published with respect to the NIST, USA standard pressure of 101.325 kPa (1 atm), or the IUPAC standard pressure of 100.000 kPa (1 bar) [4].

Taken together, [4] and [8] indicate differing reported Everest pairs of about 34 kPa and 71°C at 8,848 m elevation [4] compared with about 260 mbar (26.39 kPa) and 69°C [8], while real weather can shift pressure a bit, changing Tb by ~±0.2–0.5°C [10].

Taken together, [1] and [4] indicate that the pressure names the boiling point.

References

[1] https://webdelprofesor.ula.ve/ciencias/isolda/libros/handbook.pdf — https://webdelprofesor.ula.ve/ciencias/isolda/libros/handbook.pdf · academic [2] https://www.nist.gov/system/files/documents/pml/div685/grp01/ITS-90_metrologia.pdf — https://www.nist.gov/system/files/documents/pml/div685/grp01/ITS-90_metrologia.pdf · government [3] Step by Step Solution — https://www.vaia.com/en-us/textbooks/chemistry/chemistry-matter-and-change-2007-edition/chapter-3/problem-40-boiling-water-at-what-temperature-would-250-ml-of/ · general [4] Boiling point — https://en.wikipedia.org/wiki/Boiling_point · general [5] Boiling points | Science | Research Starters | EBSCOhost — https://www.ebsco.com/research-starters/science/boiling-points/ · general [6] High-altitude cooking — https://en.wikipedia.org/wiki/High-altitude_cooking · general [7] What is the boiling point of water on top of Mount Everist — https://www.madsci.org/posts/archives/2000-12/976811375.Es.r.html · general [8] Boiling point - wikidoc — https://www.wikidoc.org/index.php/Boiling_point · general [9] Impacts of High Altitude on Water’s Boiling Point — https://mountainhouse.com/blogs/backpacking-hiking/effects-of-altitude-on-water-boiling-time?srsltid=AfmBOopJ9oV8SHwB95xQQVWUS8MWAAhlRAIb7cjjXJF03B7a-UfiMiP- · general [10] Boiling Point at Altitude Calculator | Water & Clausius–Clapeyron Equation — https://www.pearson.com/channels/calculators/boiling-point-at-altitude-calculator · academic [11] Does water’s boiling point change with altitude? Americans aren’t sure — https://www.pewresearch.org/short-reads/2015/09/14/does-waters-boiling-point-change-with-altitude-americans-arent-sure/ · professional [12] Fun fact: The normal boiling point of water isn't exactly 100 °C (at least not since 2019 when the definition of the Kelvin scale was changed to use the Boltzmann constant and decoupled from the triple point of water) — https://www.webel.com.au/node/3553 · general

Source quality: 2 academic, 1 government, 1 professional, 8 general.