What is R?
R = 8.314 J/(mol·K) is the universal gas constant. Also R = k_B × N_A where k_B is Boltzmann constant and N_A is Avogadro number.
Ideal Gas Law Calculator
PV = nRT
Calculate pressure, volume, moles, or temperature using the ideal gas law PV = nRT.
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Enter values above to calculate
How it calculates
1
PV = nRT — ideal gas law
2
P = nRT / V
3
n in mol, R = 8.314 J/(mol·K), T in K, V in m³, P in Pa
Formula
PV = nRT
Variable Table
| Symbol | Quantity | SI Unit |
|---|---|---|
| P | Pressure | Pa |
| V | Volume | m³ |
| n | Amount | mol |
| R | 8.314 | J/(mol·K) |
| T | Absolute temperature | K |
How to Use This Calculator
This ideal gas law calculator is built for quick physics checks and worked-problem review. Enter values in the units shown beside each input, then compare the result with the formula and variable table before using it in a longer solution. The calculator does the arithmetic, but the physics still depends on choosing a model that matches the situation.
Start by identifying the system, the known quantities, and the quantity you want to find. If a value is given in a non-SI unit, convert it before substitution. A correct numerical answer with mixed units can still be physically wrong, especially when squared units, inverse seconds, charges, temperatures, or distances are involved.
Assumptions and Limits
The formula PV = nRT is a model, not a universal description of every possible case. It assumes the quantities in the variable table are the relevant quantities for the problem and that hidden effects are either negligible or already included in the inputs. If friction, drag, relativistic speeds, changing fields, non-constant temperature, or geometry-specific effects matter, check whether a more complete model is needed.
Use the result as a magnitude and units check. Ask whether the answer has the right sign, whether it grows or shrinks when an input changes, and whether the limiting cases make sense. Setting an input to zero, doubling a quantity, or using a very large value is often enough to catch a formula choice or unit mistake before it reaches a final answer.
Worked Example
1 mol of gas at 300 K in 25 L (0.025 m³). Find pressure.
Step 1: P = nRT/V
Step 2: P = 1 × 8.314 × 300 / 0.025
Answer: P = 99,768 Pa ≈ 1 atm ✓
Common Mistakes
- T must be in kelvin — never Celsius (add 273.15)
- V in m³ (1 L = 0.001 m³)
- Ideal gas law fails at high pressure/low temperature — use van der Waals for real gases
Related
Frequently Asked Questions
When does ideal gas law break down?
At high pressures (molecules too close — interactions matter) or low temperatures (near condensation point).