Ideal Gas Law Calculator - Solve PV = nRT | Free Online Tool

An Ideal Gas Law calculator (also called a PV = nRT calculator orgas law solver) is an online tool that solves the fundamental equation of state for an ideal gas. The ideal gas law, expressed as PV = nRT, relates the pressure (P), volume (V), temperature (T), and number of moles (n) of a gas through the universal gas constant (R = 8.314 J/(mol·K)). This equation is one of the cornerstones of chemistry and thermodynamics, providing a simple yet powerful way to predict gas behavior under various conditions.

Whether you are a high school or college chemistry student, a laboratory technician, a researcher, or a professional working with pressurized systems, you will frequently need to solve gas law problems. Our free online gas law calculator allows you to enter any three of the four variables (P, V, n, T) and instantly calculates the fourth - eliminating algebraic errors and tedious unit conversions. It also supports verification mode: if you enter all four values, the calculator checks whether they satisfy the PV = nRT equation with high precision.

This ideal gas equation solver operates entirely within your browser - no data is sent to any server, ensuring your privacy and enabling offline use. It supports 7 pressure units (Pa, kPa, MPa, atm, bar, mmHg, psi), 6 volume units (m³, L, mL, cm³, ft³, gal), and 3 temperature units (K, °C, °F) - all automatically converted to base SI units before the calculation. Whether you are doing stoichiometry, studying gas‑phase reactions, or designing industrial equipment, this tool is your go‑to solution for ideal gas law problems.

Using this PV = nRT calculator is straightforward:

1. Enter any three of the four values: Pressure (P), Volume (V), Moles (n), or Temperature (T).
   Leave the fourth field empty - the calculator will solve for it.
2. Select the appropriate unit for each variable using the dropdown menus.
3. The missing variable is calculated instantly as you type (auto‑calculation).
4. If you enter all four values, the calculator will verify whether they satisfy the PV = nRT equation.
5. Copy the result using the copy button, or use the “Clear All” button to reset everything.

Example: Suppose you have 2.00 moles of an ideal gas at 300 K in a 0.500 m³ container. To find the pressure, you would enter n = 2.00, T = 300 K, V = 0.500 m³, leave P empty, and the calculator will compute the pressure in your selected unit.

Note: Temperature must be entered in Kelvin (K) for the equation to work directly; however, our calculator automatically converts Celsius (°C) and Fahrenheit (°F) to Kelvin internally.

The ideal gas law is an equation of state for an ideal gas - a hypothetical gas where molecules have zero volume and do not interact except through perfectly elastic collisions. While no real gas is perfectly ideal, many common gases (air, nitrogen, oxygen, hydrogen) behave very close to ideal at ordinary temperatures and pressures, making the equation highly useful.

The equation can be rearranged to solve for any variable:

• Find pressure: P = nRT / V
• Find volume: V = nRT / P
• Find number of moles: n = PV / (RT)
• Find temperature: T = PV / (nR)

The universal gas constant R is a fundamental physical constant with the value 8.314462618 J·mol⁻¹·K⁻¹ (exactly when using SI units). For historical and practical reasons, R also appears in other forms, such as 0.082057 L·atm·mol⁻¹·K⁻¹ when pressure is in atmospheres and volume in liters. Our calculator uses R = 8.314 J/(mol·K) internally after converting your inputs to SI units.

The universal gas constant (R) is a proportionality constant that appears in the ideal gas law. Its numerical value depends on the units used for pressure, volume, and energy. The SI value is R = 8.314462618 J·mol⁻¹·K⁻¹, which is exact under the 2019 redefinition of SI units. However, for many practical chemistry calculations, the value R = 0.082057 L·atm·mol⁻¹·K⁻¹ is more convenient when working with liters and atmospheres.

Our calculator always uses R = 8.314 J/(mol·K) internally, but it automatically converts your chosen pressure and volume units to Pa and m³ before performing the calculation. This ensures maximum accuracy without you having to remember which R value to use.

The ideal gas law is an approximation that works best underlow pressures and high temperatures. Under these conditions, gas molecules are far apart and move so quickly that intermolecular attractions and molecular volume become negligible.

At high pressures (e.g., above 100 atm) or low temperatures(near the condensation point), real gases deviate significantly from ideal behavior:

• Intermolecular attractions cause the volume to be smaller than predicted (PV less than nRT).
• Molecular volume (size of gas molecules) becomes significant, causing the volume to be larger than predicted (PV greater than nRT).

For very precise work at extreme conditions, engineers use more complex equations of state, such as the van der Waals equation (which adds correction terms for molecular attraction and volume), the Redlich‑Kwong equation, or the Peng‑Robinson equation. However, for most educational and practical engineering applications at normal temperatures and pressures (0–200 °C, 1–50 atm), the ideal gas law provides excellent accuracy.

• Completely free, no registration. Unlimited calculations with no hidden costs.
• Privacy‑first design. All calculations happen locally in your browser. Your data never leaves your device.
• Supports 7 pressure units, 6 volume units, and 3 temperature units - covering all common unit systems.
• Solves for any variable (P, V, n, T) or verifies the equation when all four are entered.
• High precision (6 decimal places) using the exact ideal gas law formula.
• Works offline after initial page load.
• Fully responsive design with resizable panels on desktop for custom workflow.