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Combined Gas Law

P1V1T1=P2V2T2\frac{P_1 V_1}{T_1} = \frac{P_2 V_2}{T_2}
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Worked example: 1 L at 1 atm, 273.15 K → 0.5 atm, 546.3 K gives 4 L. Press Try an example to run it live, then adjust anything.

Enter your known values, leave one input blank, and solves for the missing one. Tap a variable’s symbol to see what it means, with a typical value. Change any unit and the answer follows.

Where Combined Gas Law fits

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Gas Density from Molar MassPartial Pressure from Mole FractionCompressibility Factor (Z = PV/nRT)Boyle's Law
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See also

Ideal Gas Law: Both use initial pressure and initial volume.Boyle's Law: Both use initial pressure and initial volume.Charles's Law: Both use initial volume and initial absolute temperature.Compressibility Factor (Z = PV/nRT): Both use initial volume and initial absolute temperature.Van der Waals Equation of State: Both use initial volume and initial absolute temperature.Gay-Lussac's Law: Both use initial pressure and initial absolute temperature.
5 more relatedGas Volume at STP: Both use initial volume.Cavitation Number (Margin above Vapour Pressure): Both use initial pressure.Dalton's Law of Partial Pressures: Both use initial pressure.Expansion Tank Acceptance Volume: Both use initial pressure.Gauge and Absolute Pressure: Both use initial pressure.
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Combined Gas Law explained

P1V1T1P2T2V2

The combined gas law merges Boyle's, Charles's, and Gay-Lussac's laws into a single statement: for a fixed amount of gas, PV/T is constant. A weather balloon shows all three variables moving at once. Launched with 2.0 m³ of helium at 101 kPa and 288 K, it rises to where the pressure is 30 kPa and the temperature 228 K; its new volume is V₂ = P₁V₁T₂ ÷ (P₂T₁) = 2.0 × 101 × 228 ÷ (30 × 288) ≈ 5.3 m³: more than double.

Hold any one variable constant and the named laws drop out: fix T for Boyle's law, fix P for Charles's, fix V for Gay-Lussac's. Temperatures must be absolute (the ratio of 20 °C to 40 °C is not 1:2 but 293:313), and Celsius or Fahrenheit inputs convert to kelvin automatically. Add Avogadro's insight about the amount of gas n and this law becomes the full ideal gas law, PV = nRT.

Combined Gas Law formula

P1V1T1=P2V2T2\frac{P_1 V_1}{T_1} = \frac{P_2 V_2}{T_2}
Where
  • P1P_1= Initial pressure (kPa)
  • V1V_1= Initial volume (L)
  • T1T_1= Initial absolute temperature (°C)
  • P2P_2= Final pressure (kPa)
  • V2V_2= Final volume (L)
  • T2T_2= Final absolute temperature (°C)
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The gas laws

5 formulasBoyle, Charles, Gay-Lussac, the combined law and the ideal gas law — each holding one property fixed, and how they collapse into PV = nRT.

Revised 30 October 2026
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formula.expert. (2026, October 30). Combined Gas Law Formula & Calculator. https://formula.expert/solvers/combined-gas-law

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