Estimate gas molar mass from measured properties
The molar mass of gas calculator combines a measured gas mass with pressure, volume, and temperature. Enter mass in grams, select a pressure and volume unit, and use kelvin or degrees Celsius for temperature. The page converts everything to litres, atmospheres, and kelvin before using the ideal gas equation. Showing each normalized value makes it easier to identify a pressure-prefix mistake or a Celsius value that was incorrectly used as an absolute temperature.
Derive M from the ideal gas equation
Starting with PV = nRT and n = m/M gives M = mRT/(PV). The calculator uses R = 0.082057366080960 L·atm·mol−1·K−1, so pressure must be in atmospheres, volume in litres, temperature in kelvin, and mass in grams. The resulting unit is grams per mole. A gas sample of known identity should return a value near its formula molar mass when the measurements are accurate and the gas behaves approximately ideally.
Convert pressure, volume, and temperature correctly
Kilopascals, pascals, bar, and atmospheres are converted before substitution; millilitres and cubic metres are similarly converted to litres. Celsius is shifted by 273.15 to obtain kelvin. A Celsius reading below zero can still be a positive kelvin temperature, but absolute zero itself is not a valid gas-law input. Use absolute pressure rather than gauge pressure unless the source problem has already converted the measurement. Confirm that mass represents the gas alone rather than the container.
Check proportional trends and sample quality
With mass, pressure, and volume fixed, the calculated molar mass rises with temperature. With the other values fixed, it falls as pressure or volume increases. Reinsert the reported molar mass into n = m/M and verify that nRT reproduces PV. A result far from the expected identity can indicate leaked gas, residual air, water vapour, incorrect tare mass, inconsistent conditions, or non-ideal behaviour. A gas mixture produces an apparent average rather than the molar mass of one pure compound.
Ideal-gas limitations and private use
The ideal model is most reliable at relatively low pressure and away from condensation. High pressure, strong intermolecular forces, association, dissociation, and proximity to a phase boundary may require a compressibility factor or a real-gas equation. The result does not identify an unknown gas or assess toxicity, flammability, pressure-vessel safety, or ventilation. Real gas work requires suitable instruments, procedures, and qualified safety review.
The values are calculated in the current browser tab. NexaCurrent does not upload the quantities, formulas, chemical names, element choices, or other information entered here, and no account is needed. Copying is a deliberate action after the answer and working are visible. Refreshing or leaving the page clears the current calculation, so keep a copied result if it is needed for later study.