Case 1
- Initial pressure p₁
- 100
- Initial volume V₁
- 2
- Initial temperature T₁
- 300K
- Final pressure p₂
- 150
- Final temperature T₂
- 350K
1.5556
Open with these valuesCombined Gas Law Calculator
1.5556unit of V₁
Result: 1.5556 unit of V₁Pressure times volume divided by temperature stays the same for a fixed amount of gas. That one line contains Boyle, Charles and Gay-Lussac at once. Enter both pressures, both temperatures in kelvin and the starting volume; halving the pressure while doubling the kelvin quadruples the volume.
The numbers at a glance
Held fixed: Initial pressure p₁ 100.000, Initial volume V₁ 2.000, Initial temperature T₁ 300.00 K, Final pressure p₂ 150.000.
| Final temperature T₂ (K) | Result |
|---|---|
| 100.00 | 0.4444 |
| 200.00 | 0.8889 |
| 300.00 | 1.3333 |
| 350.00Your value | 1.5556 |
| 400.00 | 1.7778 |
| 500.00 | 2.2222 |
| 600.00 | 2.6667 |
| 700.00 | 3.1111 |
Worked examples
Case 2
- Initial pressure p₁
- 100
- Initial volume V₁
- 1
- Initial temperature T₁
- 250K
- Final pressure p₂
- 50
- Final temperature T₂
- 500K
4.0000
Open with these valuesCase 3
- Initial pressure p₁
- 760
- Initial volume V₁
- 22.4
- Initial temperature T₁
- 273.15K
- Final pressure p₂
- 380
- Final temperature T₂
- 546.3K
89.6000
Open with these valuesHow it's calculated
V₂ = p₁ × V₁ × T₂ ÷ (T₁ × p₂)
- StepEnter both pressures in the same unit; only their ratio matters.
- StepConvert both temperatures to kelvin: degrees Celsius plus 273.15.
- StepEnter the starting volume in any unit you like.
- ResultRead the final volume in that same unit.
Reference table
| p₁, V₁, T₁, p₂, T₂ | Change | Final volume V₂ |
|---|---|---|
| 2, 5, 400, 4, 200 | colder and squeezed | 1.2500 |
| 1, 1, 273.15, 1, 373.15 | heated only | 1.3661 |
| 100, 2, 300, 150, 350 | warmer but squeezed | 1.5556 |
| 100, 1, 250, 50, 500 | warmer and released | 4.0000 |
| 101.325, 10, 300, 202.65, 600 | both doubled | 10.0000 |
| 760, 22.4, 273.15, 380, 546.3 | both doubled | 89.6000 |
Questions
What is the combined gas law?
It states that pressure times volume divided by absolute temperature is constant for a fixed amount of gas. It merges Boyle's law, Charles's law and Gay-Lussac's law into one equation.
Which units do the pressures need?
Any, as long as both use the same one, because only their ratio enters the formula. The volume comes back in whatever unit the starting volume used.
Why must temperature be absolute?
Because the equation divides by it. A Celsius value of zero would divide by zero, and negative Celsius values would flip the sign of a volume.
When do I need the ideal gas law instead?
When the amount of gas itself changes, or when you want the number of moles rather than a before-and-after comparison. The combined law cancels the amount out.
Sources and last check
Information, not professional advice.