Ideal Gas Law Calculator

The ideal gas law connects four measurable properties of a gas: absolute pressure P, volume V, amount of substance n, and absolute temperature T. Its compact form is PV = nRT, where R is the universal gas constant. This calculator uses R = 8.314462618 J/(mol·K) and SI inputs, so pressure is entered in pascals, volume in cubic metres, amount in moles, and temperature in kelvin. Choose the quantity you want to find and provide the other three. Pressure is calculated as nRT divided by V. Volume is nRT divided by P. Amount is PV divided by RT. Temperature is PV divided by nR. These are algebraic rearrangements of the same equation, so consistent units are essential. A litre equals 0.001 cubic metre, one kilopascal equals 1,000 pascals, and Celsius is converted to kelvin by adding 273.15. Both pressure and temperature must be absolute. Gauge pressure measures a difference from the surrounding atmosphere and cannot be inserted directly. Add atmospheric pressure to gauge pressure first. Kelvin begins at absolute zero, preventing the physically meaningless negative absolute temperatures that would arise if Celsius were used directly. Volume should describe the space occupied by the gas, while amount should represent the number of moles in that same state. The word ideal identifies the assumptions behind the model. Ideal particles have negligible volume and no intermolecular attraction, and their collisions conserve energy. Real gases approximate those assumptions best at low to moderate pressure and sufficiently high temperature. At high pressure, near condensation, or close to a critical point, molecular size and attraction matter. Engineers then introduce a compressibility factor or choose a real-gas equation of state. Despite its simplifications, PV = nRT is one of the most useful relationships in chemistry and physics. It supports laboratory planning, cylinder estimates, pneumatic calculations, ventilation analysis, weather reasoning, and classroom exercises. It also makes trends easy to understand: at fixed volume and amount, pressure rises with absolute temperature; at fixed pressure and amount, volume rises with temperature; and at fixed pressure and temperature, adding gas increases volume. Treat the result as the state predicted by the ideal model. Significant figures should reflect the quality of the inputs, and safety-critical vessel or process calculations should use appropriate property data, design standards, and margins. For ordinary problems where ideal behavior is a sound approximation, this calculator gives a direct and transparent solution for any one of the four variables.