Calculate gas volume from PSI with Boyle’s law, or solve for initial or final pressure and volume using absolute or gauge pressure and common units.

Fixed amount of ideal gas at constant temperature. Pressure alone cannot determine volume; both gas states must be specified.

Optional settings

Gauge mode only. Blank uses 1 standard atmosphere; enter local pressure if known. The same atmosphere is used for both states.

Volume from PSI Formula

For a fixed amount of ideal gas at constant temperature, Boyle’s law relates two equilibrium states. Use absolute pressures in the following formula; PSI alone does not determine volume.

V = P1 × V1 / P2
  • Where V is the Volume from PSI (ft3)
  • P1 is the initial absolute pressure (psia)
  • P2 is the final absolute pressure (psia)
  • V1 is the initial volume (ft3) 

To calculate volume from psi, multiply the initial pressure by the initial volume, then divide by the final pressure.

Boyle’s law example: PabsV = 100 psi·ft³
Absolute pressure (psia) Volume (ft³) Volume (m³) Volume (L)
1100.0002.8322831.680
250.0001.4161415.840
333.3330.944943.893
425.0000.708707.920
520.0000.566566.336
1010.0000.283283.168
156.6670.189188.779
205.0000.142141.584
254.0000.113113.267
303.3330.09494.389
352.8570.08180.905
402.5000.07170.792
452.2220.06362.926
502.0000.05756.634
601.6670.04747.195
751.3330.03837.756
801.2500.03535.396
901.1110.03131.463
1001.0000.02828.317
1500.6670.01918.878
* Rounded to 3 decimals. Assumes a fixed ideal-gas amount and constant temperature, with PabsV = 100 psi·ft³ (V = C / Pabs). This is one example state constant, not a universal pressure-to-volume conversion. Unit refs: 1 ft³ = 0.0283168 m³ = 28.3168 L.

How to Calculate Volume from PSI?

The following examples use absolute pressure, a fixed amount of ideal gas and constant temperature. Gauge pressure must first be converted by adding the atmospheric reference.

Example Problem #1

  1. First, determine the initial psi.
    1. The initial psi is given as 4.
  2. Next, determine the final psi.
    1. The final psi  is calculated as 2.
  3. Next, determine the initial volume (ft3).
    1. The initial volume (ft3) is found to be 10.
  4. Finally, calculate the Volume from PSI using the formula above: 

V = P1 * V1 / P2

Inserting the values from above yields: 

V = 4 * 10 / 2 = 20 (ft3)

Example Problem #2

The variables needed for this problem are provided below:

initial psi = 7

final psi  = 6

initial volume (ft3) = 10

Entering these values and solving gives:

V = 7 * 10/ 6 ≈ 11.67 (ft3)