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Boiling Point Calculator

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Boiling point definitionClausius–Clapeyron relationHow to calculate the boiling pointFAQs

This boiling point calculator tells you how to calculate the boiling point of most common substances at an arbitrary pressure, based on the Clausius–Clapeyron relation. Whether you want to analyze water, ethanol, or ammonia, simply provide some reference values, and this calculator will do the work for you. Read on to learn what exactly is the boiling point definition and what equation you can use to determine its value.

Boiling point definition

The boiling point is simply the temperature at which water starts boiling — in other words, it changes its state from liquid to gas. This temperature is dependent on pressure and the substance's latent heat of vaporization. The latter property is unique for each substance — you can be sure that two samples of water will have the same latent heat. You can learn more in the latent heat calculator

Clausius–Clapeyron relation

Our boiling point calculator uses the Clausius–Clapeyron relation to establish the boiling point of any substance at a given pressure. This equation characterizes phase transitions (such as vaporization) and relates the pressure to boiling point in the following way:

ln(P₁/P₂) = -ΔH/R × (1/T₁ − 1/T₂)


  • P₁ — Pressure at state 1;
  • P₂ — Pressure at state 2;
  • T₁ — Boiling point at state 1 (at a pressure equal to P₁);
  • T₂ — Boiling point at state 2 (at a pressure equal to P₂);
  • ΔH — Latent heat of vaporization of the substance, measured in J/mol (shown for the selected substance when the Show heat of vaporization box is checked); and
  • R — Gas constant, equal to 8.314 J/(K·mol). It is also used by our ideal gas law calculator.

How to calculate the boiling point

To calculate the boiling point of a substance, follow these steps:

  1. Choose your substance. Is it water or something different? Note down its latent heat of vaporization.

  2. Perform an empirical experiment. Heat up a sample of the substance and check at what temperature it starts to boil. This will be your T₁.

  3. Measure the pressure of the surroundings (preferably using a barometer). Note down this value — it will be your P₁.

  4. Decide for what pressure you want to calculate the boiling point. This value is the P₂.

  5. Insert all of the values into the Clausius–Clapeyron equation to find the boiling point T₂. You can also use our boiling point calculator instead and save yourself some time.

This calculator has the values of P₁ and T₁ set to 1013.25 hPa and 100 °C, respectively. These values correspond to the normal atmospheric pressure at the sea level and boiling point of water. You need to set different values if you are calculating the boiling point at altitude or are analyzing a different substance (which is done for you).


What’s the boiling point of water?

The boiling point of water is 99.97 °C, or 211.95 °F, under standard pressure at sea level. Usually, you'll find that these values are rounded to 100 °C or 212 °F.

Is boiling point a physical property?

Yes, a substance's boiling point is a physical property. A physical property is a characteristic of a substance that can be observed or measured without changing the chemical identity of the substance.

What’s the boiling point?

The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid, and the liquid changes into a vapor. In other words, when the substance changes from liquid to gas.

Does salt lower the boiling point of water?

No, quite the contrary. The boiling point of seawater is 102 °C, surpassing that of freshwater, which is 100 °C at sea level. This difference is attributed to the dissociation of NaCl (sodium chloride) in water, leading to the alteration of intermolecular forces among water molecules.

How do I calculate the boiling point?

To calculate the boiling point of a given substance:

  1. Use the Clausius–Clapeyron equation:

    ln(P₁/P₂) = -ΔH/R × (1/T₁ − 1/T₂)

  2. Insert the pressure values at state 1 and state 2, P₁ and P₂.

  3. Substitute the value of temperature at the initial state T₁.

  4. Insert the values of latent heat of vaporization ΔH and the gas constant R.

  5. Rearrange to solve for the boiling point temperature T₂ and perform the necessary calculations.

  6. You’re all set!

State 1

State 2

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