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Calculator Answers

Combined Gas Law Calculator

Blake Boege
Written by Blake Boege · Founder, Calculator Answers

The combined gas law combines Boyle's law, Charles's law, and Gay-Lussac's law into a single relationship: (P1·V1)/T1 = (P2·V2)/T2. It states that the ratio of the product of pressure and volume to absolute temperature is constant for a fixed amount of gas. A combined gas law calculator solves for any of these six variables when the other five are provided. It is a fundamental thermodynamic tool in chemistry and physics.

Solve for any of the six variables in the combined gas law equation: (P₁·V₁)/T₁ = (P₂·V₂)/T₂. Select your pressure and volume units, fill in exactly 5 fields, and leave the target field blank.

See also: Ideal Gas Law Calculator, Molarity Calculator, and Dilution Calculator.

Quick Answer

Solve the combined gas law equation (P1·V1)/T1 = (P2·V2)/T2 for pressure, volume, or temperature. Leave one field blank to solve for the missing variable.

Units Configuration

Pressure Unit (shared)

Volume Unit (shared)

State 1 (Initial)

atm
L
K

Kelvin only

State 2 (Final)

atm
L
K

Kelvin only

Quick Instructions

  • Fill in exactly five variables.
  • Leave the field you want to calculate empty.
  • All temperatures must be positive and in Kelvin (K).
Calculation result

Cannot compute

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Enter exactly 5 values to solve for the 6th.

The Combined Gas Law states that for a fixed quantity of gas, the relationship of pressure, volume, and absolute temperature remains constant: (P₁ · V₁) / T₁ = (P₂ · V₂) / T₂.

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Examples

P1 = 1 atm, V1 = 2 L, T1 = 300 K, P2 = 2 atm, T2 = 300 K

V2 = 1.0 L

P1 = 100 kPa, V1 = 5 L, T1 = 273 K, V2 = 10 L, T2 = 373 K

P2 ≈ 68.3 kPa

P1 = 2 atm, V1 = 1 L, T1 = 298 K, P2 = 3 atm, V2 = 0.5 L

T2 ≈ 223.5 K

How it works

The combined gas law combines Boyle's, Charles's, and Gay-Lussac's laws into a single ratio. It assumes a constant number of moles (amount) of an ideal gas.

Combined Gas Law Formula · (P₁ · V₁) / T₁ = (P₂ · V₂) / T₂

Note: All temperatures must be in Kelvin (absolute temperature scale). Pressure and volume units must be identical on both sides of the equation.

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Ideal Gas Law CalculatorSolve PV = nRT for pressure, volume, moles, or temperature. Supports common units: atm, kPa, Pa, mmHg, psi; L, mL, m3; K, C, F. Assumes ideal gas behavior.Molarity CalculatorFind molarity, moles, volume, or mass from any three known values using M = n / V (and n = m / M when molar mass is supplied). Educational chemistry only, not lab or dosing advice.Dilution CalculatorSolve M1V1 = M2V2 for any of the four variables, find the dilution factor, and plan simple serial dilutions. Supports mL and L. Educational chemistry only, not lab or dosing advice.

Frequently asked questions

The combined gas law is an equation that merges Boyle's Law, Charles's Law, and Gay-Lussac's Law into one: (P1·V1)/T1 = (P2·V2)/T2. It shows the relationship between pressure, volume, and absolute temperature for a constant amount of gas.

Temperatures must be entered in Kelvin (K). Gas law formulas use absolute temperature scales. If your temperature is in Celsius, add 273.15 to convert it to Kelvin before entering it (e.g., 25 °C = 298.15 K).

No, as long as they are consistent. For example, if P1 is in atm, P2 must also be in atm; if V1 is in mL, V2 must be in mL. The calculator allows you to select a shared unit for pressure and a shared unit for volume to prevent mismatch errors.

The calculator checks all six input fields. If you fill in exactly five of the fields and leave one blank, it solves algebraically for the blank field.

Yes. Gay-Lussac's Law (P/T = k) is combined here alongside Boyle's Law (PV = k) and Charles's Law (V/T = k). If volume remains constant (V1 = V2), the equation simplifies directly to Gay-Lussac's law.