How to use the Ideal Gas Law Calculator
Choose one quantity to calculate, enter the other three values, and select their units. The calculator applies PV = nRT and shows the solved value.
Choose the quantity to solve for
Use Solve for to choose Pressure (P), Volume (V), Amount of gas (n), or Temperature (T). The selected quantity's input field is hidden, so only the three known values are required.
Enter values and select units
- Pressure (P): atmospheres (atm), kilopascals (kPa), pascals (Pa), millimeters of mercury (mmHg), pounds per square inch (psi), or bar.
- Volume (V): liters (L), milliliters (mL), cubic meters (m³), or cubic feet (ft³).
- Amount of gas (n): moles (mol) or millimoles (mmol).
- Temperature (T): Kelvin (K), Celsius (°C), or Fahrenheit (°F).
Enter absolute pressure; the interface does not provide a gauge/absolute pressure selector. Before calculating, the script normalizes pressure to atm, volume to L, amount to mol, and temperature to K.
Calculate and read the result
- Use Solve for to select the unknown quantity.
- Enter the other three values and select their units.
- Select Calculate. The result statistics show the solved quantity in the selected unit.
- Read Formula & steps for the normalized known values and calculation steps.
The formula uses R = 0.0820573660809596 L·atm·mol-1·K-1; the steps display the rounded value 0.0821.
Reset, copy, or download the result
Select Reset to clear the values, restore the default units, return Solve for to Pressure (P), and hide the result. After calculating, use Copy result to copy the result content or Download result (.txt) to download it as a .txt file.
Input validation and limits
Pressure, volume, and amount of gas must be finite positive numbers. Temperature must be finite and convert to a value above absolute zero. Empty values, invalid text, zero or negative values where positivity is required, and non-finite or non-positive calculated results are rejected.
Inputs must match /^-?\d*\.?\d+$/: decimal notation with an optional leading minus sign. Plus signs, exponent notation, and a trailing decimal point such as 1. are rejected. Each raw numeric input must not exceed 1e12 in absolute value.
Calculation assumptions and limitations
The tool calculates the ideal-gas relationship only. Ideal-gas behavior is a model; this calculator does not model or correct for real-gas behavior at high pressure, low temperature, or near a phase change. It does not look up properties for a specific gas, infer missing values, or present the result as certified engineering, chemistry, or professional advice.
Privacy and Local Calculation
The calculator JavaScript performs the PV = nRT calculation locally in your browser. The page also loads analytics scripts, and the local implementation does not establish whether those scripts can access or transmit form-field values.
Frequently Asked Questions
What is the ideal gas law formula?
The ideal gas law is PV = nRT, where P is pressure, V is volume, n is the amount of gas in moles, T is absolute temperature, and R is the ideal gas constant, 0.0820573660809596 L·atm per mol·K. The result steps display this as the rounded value 0.0821.
Can this calculator solve for volume, moles, or temperature, not just pressure?
Yes. Use Solve for to choose the quantity, then enter the other three known values. The calculator rearranges PV = nRT algebraically to isolate whichever value you selected.
What units does this calculator support?
Pressure can be entered in atm, kPa, Pa, mmHg, psi, or bar. Volume can be entered in liters, milliliters, cubic meters, or cubic feet. Amount of gas can be entered in moles or millimoles. Temperature can be entered in Kelvin, Celsius, or Fahrenheit, and is always converted to Kelvin before calculating.
Why does temperature have to be above absolute zero?
The ideal gas law uses absolute temperature in Kelvin. A Celsius or Fahrenheit value that converts to zero or below zero Kelvin is physically impossible, so the calculator rejects it with an explicit error instead of producing a meaningless result.
Does this tool account for real, non-ideal gas behavior?
No. It performs a deterministic calculation of the ideal gas relationship PV = nRT only. Real gases deviate from ideal behavior at high pressure, low temperature, or near a phase change, and this calculator does not model or correct for those effects.