Gas Constant (R) Values: Complete Reference Table
The gas constant R appears in the ideal gas law PV = nRT. Its numerical value depends on the units you use for pressure and volume. Use this table to find the correct R for your calculation.
Full R Values Table
| R Value | Units | Pressure | Volume | Common Usage |
|---|---|---|---|---|
| 0.08206 | L·atm/(mol·K) | atm | L | Most common in chemistry textbooks |
| 8.314 | J/(mol·K) | Pa | m³ | SI units, physics, thermodynamics |
| 8.314 | Pa·m³/(mol·K) | Pa | m³ | Same as above, explicit units |
| 8.314 | kPa·L/(mol·K) | kPa | L | P in kPa, V in liters |
| 62.36 | L·mmHg/(mol·K) | mmHg (torr) | L | Lab work with manometers |
| 1.987 | cal/(mol·K) | Energy | Thermochemistry (calories) | |
| 8.314×10³ | mL·kPa/(mol·K) | kPa | mL | Small volume calculations |
| 82.06 | mL·atm/(mol·K) | atm | mL | Small volume in atm |
How to Choose the Right R
- Check the pressure unit in your problem.
- Check the volume unit.
- Find the row in the table where both match.
- Use that R value in PV = nRT.
If your units don't match any common R value, convert them to a standard pair (e.g., atm + L) rather than looking for an unusual R.
Universal vs Specific Gas Constants
The universal gas constant R = 8.314 J/(mol·K) is the same for all ideal gases and is used in PV = nRT.
The specific gas constant Rspecific = R / M (where M is molar mass in kg/mol) is unique to each gas and is used in engineering applications:
| Gas | Molar Mass (g/mol) | Rspecific (J/(kg·K)) |
|---|---|---|
| Air | 28.97 | 287.0 |
| N₂ | 28.01 | 296.8 |
| O₂ | 32.00 | 259.8 |
| CO₂ | 44.01 | 188.9 |
| H₂ | 2.016 | 4124 |
| He | 4.003 | 2077 |
Use the PV=nRT Calculator — it automatically selects the correct R based on your units. See also: PV=nRT Units Guide.
Frequently Asked Questions
-
R is the universal (or ideal) gas constant that appears in PV=nRT. It relates the energy scale to temperature and amount of substance. Its numerical value depends on the units chosen for pressure and volume.
-
Match R to your pressure and volume units. Use 0.08206 for atm and L, 8.314 for kPa and L (or Pa and m³), 62.36 for mmHg and L. If unsure, convert your units to atm and L and use R = 0.08206.
-
The universal gas constant R = 8.314 J/(mol·K) applies to all gases. The specific gas constant R_specific = R/M (where M is molar mass) is different for each gas. For example, for air: R_specific = 8.314/28.97 = 0.2870 kJ/(kg·K).