Gas Laws Calculator — Combined & Ideal Gas Law Solver(P₁V₁)/T₁ = (P₂V₂)/T₂ · PV = nRT · Boyle's · Charles' · Gay-Lussac's
Use this free Gas Laws Calculator to instantly solve any unknown gas state variable — including pressure (P) in atm, kPa, or mmHg, volume (V) in litres or m³, and temperature (T) in Kelvin (K) — using the Combined Gas Law formula: (P₁V₁) / T₁ = (P₂V₂) / T₂ and the Ideal Gas Law equation: PV = nRT — where n is the number of moles of gas and R = 8.314 J/mol·K is the universal gas constant. This calculator incorporates all three foundational gas law relationships: Boyle's Law — P ∝ 1/V (constant temperature) · Charles' Law — V ∝ T (constant pressure) · Gay-Lussac's Law — P ∝ T (constant volume) — enabling complete gas pressure, volume, and temperature calculations under any combination of changing conditions.
This online gas law calculator is applied across a wide range of chemistry, physics, and engineering disciplines: chemistry lab calculations — STP & NTP gas volume problems · thermodynamic cycle analysis — Carnot, Otto & Diesel cycles · HVAC, refrigeration & pneumatic system pressure calculations · scuba diving — Boyle's Law depth & pressure calculations · aerospace & meteorology — altitude and atmospheric pressure · industrial gas storage — cylinder pressure & tank volume sizing. Trusted by chemistry students, A-Level and AP Chemistry learners, chemical engineers, thermodynamics researchers, HVAC engineers, and physics educators for precise ideal and real gas behavior calculations based on the kinetic molecular theory of gases and van der Waals equation for non-ideal gases.
⚠ Chemistry Disclaimer: This gas laws calculator is intended for educational, academic, and estimation purposes only. All calculations assume ideal gas behavior where gas molecules have no intermolecular forces and negligible molecular volume — conditions that break down for real gases at high pressure (above 10 atm), low temperature (near condensation point), and for polar molecules and heavy gases. Always use absolute temperature in Kelvin (K = °C + 273.15) — never Celsius or Fahrenheit — to avoid calculation errors. For real gas behavior, apply the van der Waals equation: (P + a/V²)(V − b) = nRT. Verify all results with a qualified chemistry or chemical engineering professional for safety-critical industrial gas applications.
Gas laws describe the fundamental physical relationships between the pressure (P), volume (V), and temperature (T) of a gas sample — three interconnected state variables that govern all ideal gas behavior in chemistry, physics, and thermodynamics. The Combined Gas Law unifies three foundational gas law equations into a single powerful expression: (P₁V₁)/T₁ = (P₂V₂)/T₂ — merging Boyle's Law (pressure is inversely proportional to volume at constant temperature: P₁V₁ = P₂V₂), Charles' Law (volume is directly proportional to temperature at constant pressure: V₁/T₁ = V₂/T₂), and Gay-Lussac's Law (pressure is directly proportional to temperature at constant volume: P₁/T₁ = P₂/T₂) — enabling accurate gas pressure, volume, and temperature calculations whenever two of the three state variables change simultaneously while the amount of gas (moles, n) remains constant. These gas law calculations are foundational in chemistry lab experiments, thermodynamic cycle analysis, HVAC and refrigeration engineering, scuba diving pressure calculations, and aerospace altitude and atmospheric pressure problems.
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Gas Laws Calculator — Boyle's, Charles', Gay-Lussac's, and Combined in One Tool
The three classical gas laws each isolate one pair of variables while holding the third constant. Boyle's Law (P₁V₁ = P₂V₂) applies at constant temperature: doubling pressure halves volume. Charles' Law (V₁/T₁ = V₂/T₂) applies at constant pressure: doubling absolute temperature doubles volume. Gay-Lussac's Law (P₁/T₁ = P₂/T₂) applies at constant volume: heating a sealed container proportionally increases pressure. The gas laws calculator handles all three as special cases and also solves the combined law where none of the variables are held constant.
Practical applications appear in every pressurized system. A scuba tank at 20°C contains air at 200 bar. Left in a car on a 50°C summer day, the pressure rises to 200 × (323/293) = 220.5 bar — explaining why compressed gas cylinders should never be stored in hot environments. A weather balloon filled to 1 m³ at sea level (101 kPa) expands to 10 m³ at altitude where pressure is 10 kPa — and must be sized to burst at the right altitude for scientific payload recovery. The calculator makes these safety-relevant calculations fast and accurate.
Absolute temperature (Kelvin) is mandatory for all gas law calculations. Gas law ratios are proportional only when temperature is in Kelvin — using Celsius produces grossly wrong answers. 20°C (293 K) doubled in Kelvin is 586 K = 313°C, not 40°C. This is the most common error in gas law problems. The calculator accepts both Celsius and Kelvin inputs but always converts to Kelvin for the calculation, with the Kelvin values displayed so the conversion is transparent and verifiable.