# Ideal Gas Law Calculator (PV = nRT)

Free ideal gas law calculator. Calculate pressure, volume, moles, or temperature using PV = nRT. Step-by-step solutions with STP comparisons.

## What this calculates

Calculate any variable in the ideal gas law: PV = nRT. Enter three known values and solve for the fourth. Uses R = 0.08206 L·atm/(mol·K).

## Inputs

- **Solve For** — options: Pressure (P), Volume (V), Moles (n), Temperature (T) — Select which variable to calculate.
- **Pressure (P)** (atm) — min 0 — Pressure in atmospheres.
- **Volume (V)** (L) — min 0 — Volume in liters.
- **Moles (n)** (mol) — min 0 — Amount of gas in moles.
- **Temperature (T)** (K) — min 0 — Absolute temperature in Kelvin (K = °C + 273.15).

## Outputs

- **Result** — The calculated value.
- **Unit** — formatted as text — Unit of the result.
- **Formula** — formatted as text — Step-by-step calculation using PV = nRT.
- **STP Reference** — formatted as text — Comparison to standard temperature and pressure conditions.

## Frequently Asked Questions

**Q: What is the ideal gas law?**

A: The ideal gas law PV = nRT relates pressure (P), volume (V), amount (n in moles), and temperature (T in Kelvin) of an ideal gas. R is the universal gas constant (0.08206 L·atm/(mol·K)).

**Q: What is STP?**

A: STP (Standard Temperature and Pressure) is 0°C (273.15 K) and 1 atm. At STP, one mole of any ideal gas occupies 22.414 liters (the molar volume).

**Q: When does the ideal gas law fail?**

A: The ideal gas law fails at high pressures, low temperatures, and for gases with strong intermolecular forces. Under these conditions, real gas equations like the van der Waals equation provide better results.

**Q: Why must temperature be in Kelvin?**

A: The ideal gas law requires absolute temperature because gas volume is proportional to absolute temperature. Using Celsius would give wrong results since 0°C is not truly zero temperature.

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Source: https://vastcalc.com/calculators/chemistry/ideal-gas-chemistry
Category: Chemistry
Last updated: 2026-04-21