HesapHanem

Combined Gas Law Calculator

Solve the combined gas law.

How it is calculated

The combined gas law links pressure, volume and temperature for a fixed amount of gas: P₁V₁ / T₁ = P₂V₂ / T₂. The tool solves for the final pressure: P₂ = P₁ × V₁ × T₂ / (T₁ × V₂). Temperatures T₁ and T₂ must be in kelvin (K = °C + 273.15), and T₁ and V₂ must be above zero. The pressure unit you enter for P₁ (atm, kPa, bar) is the unit of the answer, and V₁ and V₂ only need to share one unit, because the units cancel out in the ratio. The result is rounded to two decimals. It assumes an ideal gas and a closed system with no gas added or lost; it works as a combination of Boyle's, Charles's and Gay-Lussac's laws.

Worked example

A gas starts at 1 atm, 10 L and 300 K. It is compressed to 5 L and warmed to 350 K. Then P₂ = 1 × 10 × 350 / (300 × 5) = 3,500 / 1,500. This gives 2.33 atm. The volume was halved, which would double the pressure on its own, and the temperature rise adds another factor of 350/300 ≈ 1.17. Together they raise the pressure by a factor of about 2.33.

Try this example →

Common mistakes

  • Entering temperatures in Celsius or Fahrenheit. The law needs kelvin; using 27 °C and 77 °C directly gives a wrong ratio.
  • Mixing volume units between the two states, such as V₁ in litres and V₂ in millilitres.
  • Using gauge pressure (as read from a tyre gauge) instead of absolute pressure. Add the atmospheric pressure first.
  • Applying it when gas escapes, is added, or reacts, because the amount of gas must stay the same.

About this calculator

This calculator solves the combined gas law, P₁V₁/T₁ = P₂V₂/T₂, for an unknown final pressure, volume, or temperature. It merges Boyle's, Charles's, and Gay-Lussac's laws into one equation for tracking a fixed amount of gas as pressure, volume, and temperature all change together.

Chemistry and physics students use it to solve gas-law problems without juggling three separate formulas, and it's the same relationship used to predict how a sealed gas container behaves when heated, cooled, compressed, or expanded.

Was this helpful?

You can pick up to 3 reactions.

Comments (1)

  • Editorial team

    A familiar case is a car tyre on a warm day, where the volume stays roughly constant, so enter the same volume twice. Take 2.2 bar gauge, which is about 3.2 bar absolute. Warmed from 15 to 35 °C, expressed as 288.15 K and 308.15 K, it ends near 3.4 bar absolute, or about 2.4 bar gauge. Subtract the atmosphere again afterwards. What gas situation are you checking?

Popular calculators

Loan Calculator

Monthly payment, total interest and full amortization schedule.

Percentage Calculator

Percent change, percent of, and ratio calculations.

Discount Calculator

Calculate final price, savings, and discount amount.

BMI Calculator

Body mass index from height and weight (metric or imperial).

Age Calculator

Compute your exact age in years, months and days from a birth date.

Compound Interest Calculator

Calculate the final amount and interest earned with compounding.

All Calculators