# Molar Volume Calculator

Calculate molar volume of a gas at STP or custom conditions. Uses the ideal gas law (PV = nRT) with step-by-step solution.

## What this calculates

Calculate the volume occupied by one mole of gas at standard temperature and pressure (STP) or at any custom conditions. Based on the ideal gas law, PV = nRT.

## Inputs

- **Conditions** — options: STP (0 °C, 1 atm), Custom Temperature & Pressure — Use standard conditions or enter your own.
- **Temperature** (°C) — min -273.15 — Temperature in degrees Celsius (used in custom mode).
- **Pressure** (atm) — min 0.001 — Pressure in atmospheres (used in custom mode).
- **Amount of Gas** (mol) — min 0 — Number of moles of gas. Use 1 to find the molar volume directly.

## Outputs

- **Molar Volume** (L/mol) — Volume occupied by one mole of gas.
- **Total Volume** (L) — Volume occupied by the given number of moles.
- **Temperature (K)** (K) — Temperature in Kelvin used in the calculation.
- **Calculation Steps** — formatted as text — Step-by-step calculation using the ideal gas law.

## Details

Molar volume is the volume one mole of a substance occupies. For gases, this depends almost entirely on temperature and pressure, not the identity of the gas (as long as it behaves ideally).

**At STP (0 degrees C, 1 atm)**

One mole of any ideal gas occupies 22.414 L. This is the classic number you memorize in general chemistry.

**At Room Temperature (25 degrees C, 1 atm)**

Molar volume = RT/P = 0.08206 x 298.15 / 1 = 24.47 L/mol. Warmer gas takes up more space.

**The Ideal Gas Law**

PV = nRT, where:
- P = pressure in atm
- V = volume in liters
- n = moles of gas
- R = 0.08206 L atm / (mol K)
- T = temperature in Kelvin

Rearranging for molar volume: V/n = RT/P

**When Does This Break Down?**

The ideal gas law works well at moderate temperatures and low pressures. At very high pressures or very low temperatures, real gases deviate because molecules have actual volume and attract each other. Use the van der Waals equation for those conditions.

## Frequently Asked Questions

**Q: What is the molar volume at STP?**

A: At standard temperature and pressure (0 degrees C, 1 atm), the molar volume of an ideal gas is 22.414 L/mol. This value applies to any ideal gas regardless of its molecular identity.

**Q: Why is molar volume the same for all ideal gases?**

A: The ideal gas law (PV = nRT) does not include any term for molecular size or identity. At a given temperature and pressure, one mole of any ideal gas occupies the same volume because gas molecules are far apart and their individual properties do not affect the bulk volume.

**Q: What is the difference between STP and standard conditions?**

A: STP is defined by IUPAC as 0 degrees C (273.15 K) and exactly 1 atm (101.325 kPa). Some textbooks use 25 degrees C and 1 bar as 'standard conditions,' which gives a slightly different molar volume of about 24.8 L/mol. Always check which convention your course uses.

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Source: https://vastcalc.com/calculators/chemistry/molar-volume
Category: Chemistry
Last updated: 2026-04-08