Tyre Pressure Temperature Calculator
How tyre pressure changes with temperature, in bar, psi and as a percentage.
Results
Pressure
2.0740
bar
Difference
-0.2260
bar
Pressure
30.08
psi
Percentage
-9.827
%
What this tool does
This is why the warning light appears on the first cold morning of autumn: the air in the tyre has not leaked, it has cooled. Roughly a tenth of a bar is lost for every ten degrees of drop. Always set pressures on cold tyres — after driving, they read high and adjusting then leaves you underinflated.
Formula
P₂ = (P₁ + Patm) × T₂ ÷ T₁ − Patm (Gay-Lussac, volume constant)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
p1 | Pressure | bar |
t1 | Initial temperature | °C |
t2 | Final temperature | °C |
pa | Atmospheric pressure | bar |
P2 | Pressure | bar |
DP | Difference | bar |
PS | Pressure | psi |
PC | Percentage | % |
Worked example
- Pressure2.3 bar
- Initial temperature20 °C
- Final temperature0 °C
- Atmospheric pressure1.013 bar
- Pressure2.0740 bar
- Difference-0.2260 bar
- Pressure30.08 psi
- Percentage-9.827 %
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.
- For work that must comply with a standard or be signed off, check the result against the applicable code and have it reviewed by a qualified engineer.