About this tool
The Gas Laws Calculator is a free, in-browser chemistry tool for two-state gas problems: it relates an initial state and a final state through P₁V₁/T₁ = P₂V₂/T₂. Choose Boyle's law (constant temperature), Charles's law (constant pressure), Gay-Lussac's law (constant volume), or the combined gas law, leave one box blank, and it solves for that unknown.
This differs from an ideal-gas PV = nRT calculator: it compares two states of the same fixed amount of gas rather than involving moles or the gas constant. Everything is computed locally in your browser, so your values never leave your device.
Temperatures must be absolute for the ratios to work, so enter them in kelvin, or switch the unit selector to °C and the tool converts by adding 273.15 before solving and shows the resolved temperatures back in kelvin. Pressures and volumes may be in any units you like as long as each pressure pair and each volume pair are consistent.
Frequently asked questions
How is this different from the ideal gas law tool?
This is a two-state (before/after) solver using P₁V₁/T₁ = P₂V₂/T₂ for a fixed amount of gas. It does not use moles or the gas constant R — for PV = nRT with moles, use the separate ideal-gas calculator.
Why must temperatures be in kelvin?
The gas-law ratios are only valid with absolute temperature. Enter kelvin directly, or choose °C and the tool adds 273.15 before calculating; results are reported in kelvin. A temperature at or below 0 K is rejected.
What does each mode hold constant?
Boyle's law holds temperature constant (P₁V₁ = P₂V₂), Charles's law holds pressure constant (V₁/T₁ = V₂/T₂), Gay-Lussac's law holds volume constant (P₁/T₁ = P₂/T₂), and the combined law varies all three.
What units do pressure and volume use?
Any consistent units — atm, kPa, mmHg for pressure and L, mL, m³ for volume — as long as P₁ and P₂ share one unit and V₁ and V₂ share one unit, because they appear as ratios that cancel.
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