Combined Gas Law (P₁V₁/T₁ = P₂V₂/T₂)

When n is constant, all of P, V, T can change. Solve for any one.

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Result

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How to use this calculator

  • Enter the 5 known values + pick which to solve.
  • Read result.

About this calculator

Combined gas law: P₁V₁/T₁ = P₂V₂/T₂ for fixed amount of gas. Combines Boyle, Charles, and Gay-Lussac into one. Useful when all three properties change. Hot air balloon rising into colder, lower-pressure air: V grows (T drops slower than P drops). T must be in Kelvin.

Frequently asked

Difference from ideal gas law?+
Combined: same gas, two states. Ideal: absolute formula PV = nRT. Use combined when transforming between conditions; ideal when finding absolute properties.
When n changes?+
Use ideal gas law twice (once for each state). Or include molar fraction if mixing gases.
Kelvin?+
Always — gas laws use absolute temperature.
Real gases?+
Combined law also breaks down at high P / low T. Same caveats as ideal gas law.
Pressure units consistent?+
Yes — both sides same units (psi, atm, kPa). Same for volume.

Related calculators

Ideal Gas Law (PV = nRT)
Solve for any of P, V, n, T given the other three. R = 8.314 J/(mol·K).
Boyle's Law (P₁V₁ = P₂V₂)
Constant T, constant n: pressure × volume = constant.
Charles's Law (V₁/T₁ = V₂/T₂)
Constant P: volume scales linearly with absolute temperature.
Avogadro's Law (V₁/n₁ = V₂/n₂)
At constant T, P: volume scales with number of moles.
Atomic Mass from Isotopes Calculator
Σ (isotope mass × abundance fraction). Periodic-table atomic mass from isotope mix.
Henderson-Hasselbalch (Buffer pH)
pH = pKa + log([A⁻]/[HA]). Predict buffer pH from acid + conjugate base concentrations.

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