What is the molar volume of a gas at STP?

At 0°C and 1 atm, one mole of any ideal gas fills 22.414 L. At the older STP definition of 1 bar it's 22.711 L; at 25°C and 1 atm it's about 24.465 L.

How many moles is 44.8 liters of gas at STP?

44.828 ÷ 22.414 ≈ 2.00 mol. Notice the gas identity doesn't matter — 2 mol of helium and 2 mol of CO₂ occupy the same 44.8 L at STP.

How do you convert moles to liters?

For a gas, multiply moles by the molar volume: at STP that is 22.4 L/mol, so 0.5 mol fills 11.2 L. For a solution, divide moles by the molarity: 0.50 mol of a 2.0 M solution is 0.250 L.

How many moles are in a liter?

For an ideal gas at STP, 1 L holds 1/22.4, or about 0.0446 mol. For a solution, the number of moles in a liter is its molarity, so a 0.5 M solution has 0.5 mol per liter.

What if my gas isn't at STP?

Change the molar volume to match your conditions. Compute it from the ideal gas law: molar volume = RT ÷ P. At 25°C and 1 atm that's 24.465 L/mol.

Why does gas identity not matter but liquid identity does?

Avogadro's law: equal volumes of ideal gases at the same temperature and pressure hold equal numbers of molecules, because gas molecules are mostly empty space. Liquids are packed, so their molar volume depends on molecular size and mass.

Does this work for real gases?

It's an ideal-gas approximation. Near room conditions most common gases are within about 1% of ideal. At high pressure or near a condensation point, real-gas behaviour diverges and you need a compressibility factor.

Can I use it for liquids?

No. For a liquid, convert through mass and molar mass instead: moles = mass ÷ molar mass.

Liters to Moles Calculator

Volume as a stand-in for a mole count

Gases have a property that makes them unusually easy to work with: at a fixed temperature and pressure, a mole of any ideal gas takes up the same volume, no matter what the gas is. This is Avogadro’s law, and it means you can measure moles of gas with a graduated cylinder or a gas syringe instead of a balance. The number that ties volume to moles is the molar volume — 22.414 L per mole at 0°C and 1 atm, the definition of STP most textbooks use.

The one thing you must nail down is the conditions. Molar volume depends on temperature and pressure, so a volume measured on a warm day corresponds to fewer moles than the same volume at STP.

The liters to moles formula

is moles, is the gas volume in litres, and is the molar volume in L/mol. If you know the actual temperature and pressure, get from the ideal gas law:

with L·atm·mol⁻¹·K⁻¹, in kelvin, and in atm.

Worked example

The calculator’s defaults are 44.828 L at the STP molar volume of 22.414 L/mol.

Two moles — and it would be two moles whether the gas were hydrogen, oxygen, or carbon dioxide. As a molecule count that’s .

Liters to Moles Calculator worked example diagram — A visual read of the worked example above — the same numbers the calculator returns for its default inputs.

Molar volume at different conditions

Conditions	Molar volume (L/mol)	44.828 L is
0°C, 1 atm (STP)	22.414	2.000 mol
0°C, 1 bar	22.711	1.974 mol
25°C, 1 atm	24.465	1.833 mol
20°C, 1 atm	24.055	1.864 mol
100°C, 1 atm	30.619	1.464 mol

The same 44.8 L holds noticeably fewer moles when it’s warm, because the gas has expanded.

Where gas-volume-to-moles is used

Gas-collection experiments. Measure the volume of hydrogen from a metal–acid reaction, convert to moles, back-calculate the metal.
Combustion analysis. CO₂ and H₂O volumes from burning a sample give moles of carbon and hydrogen.
Stoichiometry with a gaseous reactant or product, where the balanced equation’s mole ratio predicts a volume.
Respirometry and gas exchange in biology and environmental work.

Moles to liters: going the other way

The same molar volume converts in reverse. Multiply moles by the molar volume instead of dividing:

At STP, 0.5 mol of any ideal gas fills L. At room conditions (25°C and 1 atm), where the molar volume is about 24.5 L/mol, the same 0.5 mol takes up about 12.2 L. So “how many liters in a mole?” has the answer 22.4 L at STP and about 24.5 L at room temperature.

Liters of a solution to moles

If the liters are a solution rather than a gas, molar volume doesn’t apply. Use the solution’s concentration (its molarity, in mol/L) instead:

For 0.250 L of a 2.0 M salt solution, mol. Here “how many moles in a liter” simply means the molarity: a 2.0 M solution has 2.0 moles in every liter. The molarity calculator works this both ways.

Common mistakes

Using 22.4 L/mol when the gas is at room temperature, not 0°C — that overstates the moles by about 8%.
Forgetting to correct for water vapour when a gas is collected over water; subtract the vapour pressure first.
Applying it to a liquid or a dissolved gas. Molar volume is for the gas phase only.

To compute the exact molar volume for your conditions, use the ideal gas law calculator. For mass-based amounts, see the mole calculator.

About the formula: Moles = Volume (L) ÷ Molar Volume (L/mol). At STP (0°C, 1 atm), molar volume is 22.414 L/mol. At 25°C and 1 atm, it's approximately 24.465 L/mol.