This ideal gas law calculator helps students, engineers, and scientists quickly solve PV = nRT with rigorous unit handling and inline validation. Choose which variable to solve for, enter the known values in any supported units, and get accurate results instantly.

Data Source and Methodology

Authoritative source: CODATA Recommended Values of the Fundamental Physical Constants (2018), NIST SP 961. Gas constant: R = 8.314462618 J·mol⁻¹·K⁻¹. See: NIST — Fundamental Constants. Complementary definition of the ideal gas law: IUPAC Gold Book.

Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.

The Formula Explained

LaTeX: PV = nRT
LaTeX: P = \dfrac{nRT}{V} \quad;\quad V = \dfrac{nRT}{P} \quad;\quad n = \dfrac{PV}{RT} \quad;\quad T = \dfrac{PV}{nR}
LaTeX: R = 8.314462618\ \mathrm{J\cdot mol^{-1}\cdot K^{-1}} = 8.314462618\ \mathrm{Pa\cdot m^3\cdot mol^{-1}\cdot K^{-1}}

All values are converted internally to SI (Pa, m³, mol, K) to apply the equation consistently.

Glossary of Variables

P — Pressure
Force per unit area exerted by the gas (Pa, kPa, bar, atm, mmHg, psi).
V — Volume
Space occupied by the gas (m³, L, mL).
n — Amount of substance
Number of moles of gas (mol). 1 mol = 6.02214076×10²³ entities.
T — Temperature
Absolute temperature in Kelvin (K). °C is converted to K by adding 273.15.
R — Gas constant
R = 8.314462618 J·mol⁻¹·K⁻¹ (Pa·m³·mol⁻¹·K⁻¹), CODATA 2018.
M — Molar mass (optional)
g/mol; if provided, mass m = n·M (g) and density ρ = m/V (g/L) are reported.

How It Works: A Step-by-Step Example

Goal: Find the pressure of 1.000 mol of gas at 300.00 K occupying 24.615 L.

  1. Choose “Solve for Pressure (P)”.
  2. Enter V = 24.615 L, n = 1.000 mol, T = 300.00 K.
  3. Convert units to SI: V = 24.615 L = 0.024615 m³; T already in K; n in mol.
  4. Apply LaTeX: P = \dfrac{nRT}{V} = \dfrac{1.000\times 8.314462618 \times 300.00}{0.024615} ≈ 101325\ \mathrm{Pa}.
  5. Secondary units: ≈ 101.325 kPa ≈ 1.000 atm ≈ 1.01325 bar.

Frequently Asked Questions (FAQ)

When should I use the ideal gas law?

Use it for gases at relatively low pressure and high temperature where intermolecular forces are negligible. It is widely applicable for classroom and many engineering approximations.

How does the calculator handle units?

All inputs are converted to SI units internally (Pa, m³, mol, K), using precise conversion factors. Results are then displayed in user-friendly units as well.

Can I input temperature in Celsius?

Yes. The calculator converts °C to K by adding 273.15. Entering values below −273.15 °C is disallowed.

What about gauge vs absolute pressure?

Use absolute pressure with the ideal gas law. If you have gauge pressure, add atmospheric pressure (≈ 101.325 kPa at sea level) to obtain absolute pressure.

Why do I get slightly different results than textbooks?

Differences often come from rounding, different R values, or unit conversions. This tool uses CODATA 2018 R and high-precision conversion constants.

Can this tool compute number of molecules?

Yes. It reports molecules using Avogadro’s number from the computed moles.

Will this handle real gas effects?

No. For high accuracy at high pressure/low temperature, use real gas models (e.g., van der Waals, Redlich–Kwong) with appropriate parameters.

Tool developed by Ugo Candido. Content verified by CalcDomain Editorial Team.
Last reviewed for accuracy on: .