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Reader task: a researcher or student needs the boiling point of ethanol with its pressure, and needs to know how it moves under vacuum and why 95% ethanol does not boil higher.
Short answer: what is the boiling point of ethanol?
Pure ethanol (CAS 64-17-5) boils at about 78.3 °C (173 °F, 351.5 K) at standard atmospheric pressure, 760 mmHg (1.01325 bar). The NIST WebBook gives 351.5 ± 0.2 K, averaged from 138 of 148 collected values. Under reduced pressure it boils much lower, and ethanol is flammable well below its boiling point.
Definition and scope
A boiling point is only meaningful with a stated pressure. This page treats ethanol as a laboratory solvent and reagent and gives sourced values from the NIST Chemistry WebBook, PubChem (CID 702) and ILO/WHO International Chemical Safety Card (ICSC) 0044, all read 2026-11-07. It is a bench reference, not guidance on consumption or on any clinical use.
Why published boiling points differ in the second decimal
The values below are all for the same substance. They differ because they come from different compilations, and most do not say which pressure they apply to.
| Source | Reported value | Pressure stated? |
|---|---|---|
| NIST WebBook | 351.5 ± 0.2 K (about 78.4 °C) | Normal boiling point |
| PubChem, CRC Handbook 95th ed. via HSDB | 78.24 °C | No |
| PubChem, PAC database (US DOE) | 78.29 °C | 760 mmHg |
| PubChem, CAMEO citing NTP 1992 | 173.3 °F | 760 mmHg |
| ICSC 0044 | 78 °C | No |
For a methods section or lab notebook, 78.3 °C at 1 atm is a defensible round value. Quote 78 °C only when the pressure is also given or is clearly ambient.
Ethanol boiling point in Celsius, Fahrenheit and kelvin
351.5 K minus 273.15 gives 78.35 °C, about 173 °F. The last digit depends on which row above you choose, which is why K, °C and °F figures from different sites can look inconsistent.
Boiling point of 95% ethanol: the azeotrope
Ethanol and water form a minimum-boiling azeotrope at roughly 95.6% ethanol by weight, reported at about 78.2 °C (teaching sources such as Smith College and LibreTexts, citing early work by Evans, 1916). So 95% ethanol boils at about 78.2 °C, essentially the same as pure ethanol, not at a temperature between ethanol and water (100 °C). The practical consequence is that ordinary distillation cannot take an ethanol-water mixture past about 95.6%. Decimals vary between sources, so treat them as approximate. For how separation works in practice, see our guide to fractional distillation.
Ethanol boiling point under vacuum
NIST publishes Antoine equation constants for ethanol, log10(P/bar) = A − B/(T + C), with T in kelvin. For 273 to 351.70 K (Kretschmer and Wiebe, 1949): A = 5.37229, B = 1670.409, C = −40.191. Solving for T gives the table below. These are our calculated values from the NIST constants, not measured data, rounded to 0.1 °C.
| Pressure | Calculated boiling point |
|---|---|
| 1013 mbar (1 atm) | 78.3 °C |
| 500 mbar | 61.5 °C |
| 200 mbar | 42.2 °C |
| 100 mbar | 29.2 °C |
The second NIST set (Ambrose and Sprake, 1970; 292.77 to 366.63 K; A = 5.24677, B = 1598.673, C = −46.424) agrees to 0.1 °C at 1013, 200 and 100 mbar and gives 61.4 °C at 500 mbar. The practical reading for evaporation work: ethanol can boil at a bath temperature well below 78 °C if the vacuum is deep enough, so the boiling temperature at your working pressure, not the atmospheric value, governs how a solvent behaves. Each Antoine fit is valid only inside its stated temperature range.
Other ethanol properties on one card
| Property | Value | Source |
|---|---|---|
| Melting (freezing) point | −114 °C (NIST: 159 ± 2 K) | ICSC 0044; NIST |
| Relative density | 0.79 (water = 1) | ICSC 0044 |
| Vapour pressure | 5.8 kPa at 20 °C | ICSC 0044 |
| Enthalpy of vaporization | 42.3 ± 0.4 kJ/mol | NIST |
| Critical point | 514 ± 7 K, 63 ± 4 bar | NIST |
| Log Pow (octanol-water) | −0.32 | ICSC 0044 |
| Solubility in water | Miscible | ICSC 0044 |
Miscibility with water is why aqueous ethanol mixtures are common, and why the azeotrope above exists.
Is ethanol flammable or explosive?
It is a flammable liquid. ICSC 0044 lists a flash point of 12.0 °C (closed cup), an auto-ignition temperature of 400 °C and explosive limits of 3.1 to 27.7 vol% in air. The NIOSH figures quoted in our ethyl alcohol guide differ slightly (flash point 55 °F, about 12.8 °C; limits 3.3 to 19%), so cite the source you used. The flash point is far below the 78 °C boiling point: ethanol vapour can form an ignitable mixture with air at room temperature long before the liquid boils. See flammable liquid storage cabinet requirements and GHS classification of chemicals. Always follow the supplier’s safety data sheet and your site’s procedures.
Ethanol compared with water and isopropanol
Water boils at 100 °C at 1 atm, so ethanol evaporates more readily. For a solvent comparison, see isopropyl alcohol vs ethanol.
Common misunderstandings
- A boiling point without a pressure is incomplete; vacuum lowers it substantially.
- 95% ethanol does not boil at an intermediate temperature; it boils near the azeotrope value, close to pure ethanol.
- Boiling point is not the hazard threshold: flammability begins at the flash point.
FAQ
What is the boiling point of ethanol?
About 78.3 °C (173 °F, 351.5 K) at 760 mmHg.
What is the boiling point of 95% ethanol?
About 78.2 °C. Roughly 95 to 96% ethanol sits at the ethanol-water azeotrope, so simple distillation cannot give higher purity.
Is ethanol flammable or explosive?
It is flammable (flash point 12 °C closed cup), and its vapour forms explosive mixtures with air between about 3.1 and 27.7 vol% (ICSC 0044).
Is ethanol the only drinkable alcohol?
Ethanol is the alcohol in alcoholic beverages, but laboratory ethanol is a solvent and reagent and should not be consumed. This page gives no consumption advice.
Sources
- NIST Chemistry WebBook, ethanol (CAS 64-17-5), phase change data: webbook.nist.gov, read 2026-11-07.
- PubChem, Ethanol, CID 702, boiling point section: pubchem.ncbi.nlm.nih.gov, read 2026-11-07.
- ILO/WHO ICSC 0044, Ethanol (anhydrous): inchem.org, read 2026-11-07.
- Azeotrope composition: Smith College and LibreTexts chemistry teaching pages citing Evans (1916); approximate values.
