PSI To Volume Calculator
Give this calculator a pressure in PSI and the volume the same gas occupies at 1 atmosphere, and it returns the volume that gas occupies at the higher pressure, straight from Boyle’s law. The tool treats your PSI entry as an absolute pressure (psia) and shows the single most useful number for compressed-gas work: how much space the gas actually takes up inside a cylinder, tank or line. It is a gas-storage calculator, not a unit converter, and the absolute-pressure convention is stated up front rather than buried in the fine print.
Assumes ideal-gas behavior at constant temperature (Boyle’s law). The PSI entry is treated as an absolute pressure; real gases deviate at very high pressures or low temperatures.
Quick Answer
With the pre-filled values, 20 liters of gas at 1 atm compressed to 150 PSI (absolute) occupies 1.96 liters. The math is one step: 150 ÷ 14.7 = 10.20 atm, then 20 ÷ 10.20 = 1.96 liters. Click Calculate to reproduce it, then change either input to see how steeply volume falls as pressure rises.
Key takeaways
- Boyle's law only works with absolute pressure. A gauge reading of 150 PSI is 164.7 psia, and the compressed volume is 1.79 liters, not 1.96.
- The calculator treats your PSI entry as absolute and divides it by 14.7 to get atmospheres, then applies V₂ = (1 × V₁) ÷ P₂.
- Results assume constant temperature and ideal-gas behavior. Real gases deviate noticeably above a few hundred PSI or near liquefaction.
- Every worked row in the tables below is a real run of this tool, so you can type any of them in and get the same figures back.
- Quick Answer
- How to use the PSI to volume calculator
- The Boyle's law formula behind the calculator
- Worked example: the pre-filled calculation, step by step
- Absolute vs gauge pressure: the convention this tool uses, stated plainly
- Where this calculation actually gets used
- What competing calculators miss
- Frequently asked questions
- Add This Calculator to Your Website
- References
How to use the PSI to volume calculator
Enter two numbers, click Calculate volume, and read one number. The results stay hidden until you calculate, and Reset restores the worked example.
- Enter the pressure in PSI as an absolute value: if your regulator or gauge reads 150 PSI, add 14.7 and enter 164.7. The tooltip on the input repeats this, because it is the single most common mistake in this calculation.
- Enter the volume at 1 atm in liters: for a cylinder this is usually its water capacity, the volume stamped on the shoulder. For a fill job it is the volume of gas you want to store.
- Click Calculate volume and read the result: the tool reports the compressed volume in liters to two decimals, for example "Volume at 150.00 PSI: 1.96 liters". Copy my results and Share results sit beside the answer.
- Check the validation: zero, negative, blank or non-numeric entries return "Please enter valid positive numbers." rather than a silently wrong answer.
The Boyle's law formula behind the calculator
Boyle's law says that for a fixed amount of gas at constant temperature, pressure times volume is constant: P₁ × V₁ = P₂ × V₂. Here the starting state is 1 atmosphere, so V₂ = (1 × V₁) ÷ P₂(atm), and the tool converts your PSI entry with P₂(atm) = PSI ÷ 14.7.
1 atm = 14.7 PSI = 101.325 kPa = 760 mmHg (sea-level standard)
The constant-temperature assumption is the one people skip. Boyle's law is the isothermal special case of the ideal gas law; if the gas heats as you compress it, Charles's contribution matters too. The Engineering ToolBox's Boyle's law reference states the law explicitly in terms of absolute pressure, and the pressure equivalence 1 atm = 14.696 PSI is tabulated in their pressure units reference; the tool rounds it to 14.7, which shifts results by about 0.03%, far below gauge accuracy.
Worked example: the pre-filled calculation, step by step
150 PSI (absolute) and 20 liters are pre-filled. The tool computes 150 ÷ 14.7 = 10.2041 atm, then 20 ÷ 10.2041 = 1.96 liters, and reports "Volume at 150.00 PSI: 1.96 liters". The identity row below shows the check that catches unit mistakes: at 14.7 PSI the volume must come back unchanged.
More verified runs, each reproducible in the tool above:
| Pressure (PSI, absolute) | Volume at 1 atm | Tool result |
|---|---|---|
| 150 | 20 L | 1.96 liters |
| 100 | 10 L | 1.47 liters |
| 75 | 40 L | 7.84 liters |
| 300 | 5 L | 0.24 liters |
| 14.7 | 10 L | 10.00 liters (identity check) |
Absolute vs gauge pressure: the convention this tool uses, stated plainly
This tool reads your PSI entry as an absolute pressure (psia). Most gauges read psig, zeroed to atmosphere, so 150 on the dial is 164.7 psia. Enter the dial reading unchanged and you overstate the compression by roughly 10% at these pressures.
| Gauge reading | Enter in this tool | 20 L at 1 atm becomes |
|---|---|---|
| 150 psig (dial) | 164.7 | 1.79 liters |
| 150 psia (absolute) | 150 | 1.96 liters |
The check: 164.7 ÷ 14.7 = 11.2041 atm, and 20 ÷ 11.2041 = 1.79 liters. Keeping the convention visible is deliberate. Rival calculators either gloss over it or bury it in small print, and a dial-reading entered as-is quietly inflates the answer. Changing the tool to accept gauge readings would change what the tool is, so the convention stays and the disclosure stays with it.
Where this calculation actually gets used
Gas storage and handling is where PSI-to-volume earns its keep. The worked pattern is always the same: known gas volume at atmospheric pressure, known storage pressure, Boyle's law gives the space it needs.
- Gas cylinders and propane storage: a cylinder's stamped water capacity is its volume at 1 atm, so this is exactly the fill math for compressed gases. For fuel-gas specifics, the propane volume calculator handles propane's own properties.
- Scuba and breathing air: tank pressure (in absolute terms) against the tank's internal volume tells you the air supply at the surface. Divers work in absolute pressure natively, which is why the tool's psia basis matches dive planning.
- HVAC and pneumatics: receiver sizing and line-pack estimates use the same compression ratio; compressor delivery is usually quoted at standard conditions, i.e. volume at 1 atm.
- Lab gas manifolds: knowing how much bench-top gas a cylinder actually holds sets changeover schedules. At altitude the 14.7 figure shifts, see the pressure altitude calculator.
If you need the gas's volume at standard conditions from flow measurements instead, the gas volume calculator covers that direction, and the density calculator converts between a volume and a mass once the volume is known.
What competing calculators miss
The PSI-to-volume niche splits into three camps, and each leaves something on the table:
- Same-concept tools (Brave Calculator's PSI to Volume page): the closest match, and to its credit it treats the input as gauge pressure and adds the 14.7 explicitly. It stays in cubic feet with a sparse page, and its example math is not shown step by step, so a reader cannot audit the arithmetic.
- Generic Boyle's-law solvers (CFM Calculator's Boyle's Law page, Calculator Ultra's PSI tool): flexible multi-unit solving, but none of them frame the actual use case: a pressure reading and a 1-atm volume going in, a storage volume coming out. Calculator Ultra's version does not handle the PSI-to-atmosphere convention at all.
- Reference prose (Engineering ToolBox, Inspectapedia): authoritative formulas and genuinely useful worked examples, including the gauge-vs-absolute distinction, but no interactive tool. You do the arithmetic by hand.
- The gap this page fills: the exact two-input storage calculation with the absolute-pressure convention labeled on the input itself, a worked example pre-filled and hidden until you run it, a comparison table showing what changes if your reading was gauge, and an audit trail of verified runs you can reproduce to the decimal.
Frequently asked questions
PSI stands for pounds per square inch, the US customary unit of pressure. In compressed-gas work you will see psia for absolute pressure and psig for gauge pressure, and the two differ by one atmosphere, about 14.7 PSI.
Absolute. The tool divides your PSI entry by 14.7 to get atmospheres, so enter absolute pressure (psia). If your gauge reads 150 PSI, enter 164.7. Entering the dial reading unchanged overstates the compression by about 10% at these pressures.
That is Boyle's law: at constant temperature, pressure and volume of a fixed amount of gas are inversely proportional. Double the absolute pressure and the gas occupies half the volume, which is why a 20-liter-at-1-atm charge fits into 1.96 liters at 150 psia.
One standard atmosphere is 14.696 PSI at sea level, rounded to 14.7 in this calculator. It is also 101.325 kPa or 760 mmHg. The 0.03% rounding difference is far smaller than the accuracy of a typical pressure gauge.
Yes, for the volume part. Enter the tank pressure in absolute PSI and the tank's internal volume, and the tool gives the surface-equivalent air volume. It does not model breathing rate, depth profiles, or temperature changes, so treat it as a planning aid, not dive planning on its own.
Yes in reality, but not in this calculator. Boyle's law assumes constant temperature, so compressing a gas quickly and letting it heat up will give a different volume than the tool reports. For large temperature swings, a combined gas law calculation is needed.
No. Liquids are effectively incompressible, so Boyle's law does not apply to them. This tool is for gases only.
The calculator shows "Please enter valid positive numbers." instead of a result. Zero or negative pressure has no physical meaning in this formula, so the tool refuses to guess.
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References
- Engineering ToolBox. Boyle's Law (Mariotte's Law). Accessed October 23, 2026.
- Engineering ToolBox. Pressure: Units, Standard Atmospheric Pressure. Accessed October 23, 2026.
- LibreTexts Chemistry (University of Florida, CHM 2047). The Gas Laws: Boyle's Law Derivation. Accessed October 23, 2026.
- Daniel Danielsen. Boyle's Gas Law Explained with Worked Tank Examples. Accessed October 23, 2026.
- Bureau International des Poids et Mesures (BIPM). The International System of Units (SI Brochure). Accessed October 23, 2026.