Gas Volume Calculator
This gas volume calculator solves the ideal gas law, PV = nRT, for whichever variable you are missing: volume, pressure, moles or temperature, each with its own unit list. It also runs a combined gas law mode for a sample moving between two states, lets you start from grams instead of moles using a built in molar mass table, and adds a gas density figure plus an STP reference line to every ideal gas result.
Quick Answer
One mole of nitrogen at 25 °C and 1 atm occupies 24.4654 L (also printed as 24,465.404 mL and 0.02447 m³). The same amount at STP (273.15 K, 1 atm) would occupy 22.4140 L, and its density at the entered conditions is 1.1453 g/L. The calculator is pre-filled with this exact example, so one click on Calculate reproduces all three figures.
Key takeaways
- One tool, five jobs: solve for V, P, n or T in the ideal gas law, or run the combined gas law between two states.
- Temperature is converted to kelvin internally whatever unit you type, which removes the most common gas law error at the source.
- Grams are welcome: pick a gas or type a molar mass, press one button, and the moles field fills itself.
- Every ideal gas result carries a density (d = PM / RT) and an STP reference volume, so a wrong answer has something to look wrong against.
- Quick Answer
- How to use the gas volume calculator
- The formulas: one law, four rearrangements, one two-state law
- Worked example: one mole of nitrogen at room conditions
- Density and the STP line: the two extras that catch mistakes
- Where the ideal gas law, and this tool, stop being exact
- What competing calculators miss
- Frequently asked questions
- Add This Calculator to Your Website
- References
How to use the gas volume calculator
Choose what to solve for first, then fill the three known quantities in whatever units you have them. Results stay hidden until you press Calculate.
- Pick the unknown: the Solve for list offers Volume, Pressure, Moles, Temperature, or the combined gas law. In the four ideal gas modes the panel hides the variable you picked, because that is the answer, and shows an Answer unit list matched to it.
- Enter the three known values: pressure in atm, kPa, Pa, bar, psi or mmHg; volume in L, mL or m³; temperature in °C, K or °F. Every value is converted to atmospheres, litres and kelvin before the formula runs.
- Start from grams if that is what you weighed: choose the gas (nitrogen, oxygen, air, carbon dioxide, methane, helium or hydrogen) or type a custom molar mass, enter the mass, and press Convert mass to moles. The Moles field is filled to six decimal places. If you are tracking amounts in solution as well, the same mole figure feeds straight into the dilution molarity calculator.
- For a two-state problem, switch to combined mode: enter P1, V1, T1, P2 and T2 with one shared unit each for pressure, volume and temperature. The tool returns V2 in the same volume unit as V1.
- Read all three result lines: the headline answer, the same answer in the other volume units where relevant, and the extra line with the STP reference volume and the gas density.
Copy my results copies the headline and extra lines as plain text for a lab report or homework document. Reset restores the worked example below rather than blanking the form, so you always restart from numbers you can check.
The formulas: one law, four rearrangements, one two-state law
Every ideal gas mode is the same equation rearranged. The NIST CODATA listing for the molar gas constant gives the exact constant behind it; this tool uses that exact CODATA value, R = 0.082057366 L atm / (mol K), matched to litres and atmospheres.
Volume V = nRT / P | Pressure P = nRT / V | Moles n = PV / RT | Temperature T = PV / nR
Combined gas law: V2 = P1 × V1 × T2 / (T1 × P2), temperatures in kelvin
Density: d = PM / RT, with M the molar mass in g/mol
| Mode | You enter | Answer units offered |
|---|---|---|
| Volume (V) | n, T, P | L, mL, m³ |
| Pressure (P) | n, T, V | atm, kPa, psi, mmHg, bar, Pa |
| Moles (n) | P, T, V | mol only |
| Temperature (T) | P, n, V | K, °C, °F |
| Combined law (V2) | P1, V1, T1, P2, T2 | Same volume unit as V1 |
Two habits inside the code are worth knowing. First, temperatures are converted to kelvin before any ratio or product is taken, in both the ideal and combined modes, so a Celsius slip cannot silently scale an answer. Second, the conversions run through atmospheres and litres with exact factors derived from the definition 1 atm = 101325 Pa (1 kPa = 1000/101325 atm, 1 psi = 6894.757293168/101325 atm, 1 bar = 100000/101325 atm, mmHg divided by 760, Pa divided by 101325), so a pressure converts to atmospheres and back with no rounding drift at any decimal the tool prints.
Worked example: one mole of nitrogen at room conditions
Solve for volume with n = 1 mol, T = 25 °C and P = 1 atm, nitrogen selected at 28.02 g/mol. These are the pre-filled values in the calculator.
| Check | Tool output | Inputs |
|---|---|---|
| Volume of 1 mol N2 at 25 °C, 1 atm | 24.4654 L | V mode, n 1, 25 °C, 1 atm |
| Same run, density line | 1.1453 g/L | d = 1 × 28.02 / (0.082057366 × 298.15) |
| Same run, STP reference | 22.4140 L | 1 × 0.082057366 × 273.15 / 1 |
| Mass shortcut, then volume | 48.9308 L | 56.04 g N2 → 2.000000 mol, then V mode |
| Pressure round trip | 1.0000 atm | P mode, n 1, 25 °C, V 24.4654 L |
| Combined law, heated and compressed | 5.3411 L | 10 L at 1 atm, 20 °C → 2 atm, 40 °C |
The combined example rewards a second look. Doubling the pressure alone would halve 10 L to 5 L; warming from 293.15 K to 313.15 K pushes back up by a factor of 313.15 / 293.15, landing at 5.3411 L. If your combined result ever lands on the wrong side of the starting volume, one of those two effects has been entered backwards.
Density and the STP line: the two extras that catch mistakes
Density comes from the same law with the molar mass folded in: d = PM / RT, in grams per litre. It is printed whenever a molar mass is set, which is why the gas picker sits on an ideal gas page at all.
At the worked conditions the tool reports nitrogen at 1.1453 g/L. Swap the gas picker to carbon dioxide (44.01 g/mol) and the same run reports 1.7989 g/L, about 57 percent denser, which is the arithmetic behind CO2 pooling in cellars and fermentation pits. For a stand-alone mass-per-volume question with no gas law involved, the general density calculator covers liquids and solids as well. Concentration work picks up the same mole count in a different frame: once you know moles and volume, the concentration calculator expresses the mixture in the units chemists quote.
The STP line exists to expose the classic Celsius slip. Forget the kelvin conversion in a hand calculation for the worked example and you get 1 × 0.082057366 × 25 = 2.0514 L, a number that looks absurd next to any molar volume in the cards above. The tool converts for you, and the reference line gives you the habit of asking whether a gas volume per mole sits anywhere near 22 to 25 litres at ordinary conditions.
Where the ideal gas law, and this tool, stop being exact
The ideal gas law models gas particles as points with no forces between them. Real gases drift from it at high pressure (roughly above 10 atm for many gases), near their condensation temperature, and when the molecules are polar or large, like water vapour or ammonia; the NASA Glenn equation of state notes frame the same boundary for air. In those regimes a real gas equation such as van der Waals is the better model, and this page does not pretend otherwise.
Two smaller honesty notes, all verified against the code. First, the constants are exact, not rounded: R is the CODATA value 0.082057366 L atm / (mol K) and every pressure conversion derives from 1 atm = 101325 Pa exactly, so a pressure solved as exactly 1.0000 atm prints as exactly 101.3250 kPa when you switch the answer unit, and the STP molar volume prints as 22.4140 L. Second, two behaviours to know before they surprise you: entering 0 moles when solving for volume or pressure is accepted and returns a zero volume or pressure with the density line still shown, and in combined mode the answer V2 always comes back in the unit you chose for V1, because one unit list serves both states.
What competing calculators miss
Seven tools lead this keyword, and each stops one step short:
- Omni Calculator (ideal gas volume): a polished volume-only tool with a mass-to-amount helper, but volume is all it solves; pressure, moles, temperature and any two-state question send you to separate Omni pages.
- Omni Calculator (ideal gas law): solves all four variables in SI units, then splits the combined gas law, density and real gas corrections across three more calculators. One page here does the four solves plus the combined mode plus density.
- CalculatorsHub: all four rearrangements with a tidy reference table, but no mass entry, no density output, no STP reference and no combined mode.
- CalculatorLib: clean formulas, yet pressure must arrive in atmospheres and volume in litres because it offers no unit conversion at all; its own FAQ tells you to convert by hand first.
- Firgelli Automations: an engineering visualiser with density and molecule counts, engaging but slider-driven around pneumatic examples; it lacks the combined gas law and a molar mass table for starting from grams.
- OnlyCalculators: uses the precise R = 0.082057 and adds molecules and sample mass, but its worked flow centres on solving for moles, with Celsius or Kelvin as the only temperature choice and no Fahrenheit.
- UKCalculator: a broad gas laws page (Boyle, Charles, combined) that fixes temperatures in kelvin and leaves the ideal gas solve spartan, with no density or STP sanity line.
- The gap this page fills: four solves and the combined law in one card, six pressure units and three each for volume and temperature, a seven gas molar mass table with a one click grams to moles fill, and density plus STP printed on every result as a built in error check.
Frequently asked questions
PV = nRT, one equation relating the pressure, volume, amount in moles and absolute temperature of a gas through the universal gas constant R. Know any three of the four variables and the fourth follows: V = nRT / P, P = nRT / V, n = PV / RT and T = PV / nR. This calculator solves all four forms and converts your units internally before applying them.
The gas laws scale with absolute temperature, so the temperature in PV = nRT must be measured from absolute zero. Doubling a Celsius temperature does not double the thermal energy: 10 °C to 20 °C is a small change, while 283.15 K to 566.30 K is a true doubling. You can type Celsius or Fahrenheit here and the tool converts to kelvin for you, but a hand calculation must convert first.
Yes. The Solve for selector at the top of the calculator offers volume, pressure, moles and temperature, and the input panel hides whichever variable you are solving for. Each answer can be shown in several units: pressure in atm, kPa, Pa, bar, psi or mmHg, temperature in K, °C or °F, and volume in L, mL or m³. A fifth mode solves the combined gas law for a gas moving between two states.
It answers two-state questions for a fixed amount of gas: if a sample starts at pressure P1, volume V1 and temperature T1 and ends at P2 and T2, what is the final volume V2? The relation is P1V1 / T1 = P2V2 / T2, which merges Boyle’s law, Charles’s law and Gay-Lussac’s law. This tool’s combined mode solves for V2 only, using one shared unit choice each for pressure, volume and temperature across both states.
It depends which STP definition you mean, and this tool is explicit about its own: at 273.15 K and 1 atm, with the exact CODATA constant R = 0.082057366, one mole occupies 22.4140 L, the figure printed in the STP reference line. At the current IUPAC standard pressure of 100 kPa the molar volume is 22.711 L. Check which definition your course or specification uses before quoting a molar volume.
Pick your gas in the Gas selector, or type any molar mass into the Molar mass field, then enter the mass in grams and press Convert mass to moles. The tool writes mass divided by molar mass into the Moles field to six decimal places: 56.04 g of nitrogen at 28.02 g/mol becomes 2.000000 mol. You can also type moles directly and skip the mass fields entirely; they are optional.
R = 0.082057366 L atm / (mol K), the exact CODATA value of the molar gas constant in litre and atmosphere units. The pressure conversions are exact as well, because they all derive from the definitions 1 atm = 101325 Pa, 1 psi = 6894.757293168 Pa and 1 bar = 100000 Pa: converting a pressure answer to kPa multiplies by 101325/1000, which is why a 1.0000 atm result prints as exactly 101.3250 kPa.
When gases stop behaving like point particles with no intermolecular forces: at high pressures, roughly above 10 atm for many gases, at temperatures near condensation, and for polar or large molecules such as water vapour and ammonia. In those regimes a real-gas equation of state such as van der Waals tracks measurements better. For classroom work, balloons, scuba estimates at modest pressures and most gas syringes, the ideal law is well inside measurement error.
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References
- National Institute of Standards and Technology. Molar gas constant (CODATA recommended values). Accessed October 21, 2026.
- Bureau International des Poids et Mesures. The International System of Units (SI Brochure). Accessed October 21, 2026.
- NASA Glenn Research Center. Equation of State (gas laws). Accessed October 21, 2026.
- Georgia State University, HyperPhysics. Ideal Gas Law. Accessed October 21, 2026.
- National Institute of Standards and Technology, Chemistry WebBook. Nitrogen (thermophysical data). Accessed October 21, 2026.
- Royal Society of Chemistry. Nitrogen: element properties (Periodic Table). Accessed October 21, 2026.
- International Union of Pure and Applied Chemistry, Gold Book. Ideal gas (Compendium of Chemical Terminology). Accessed October 21, 2026.