Silca Tire Pressure Calculator
Silca tire pressure calculator works out Pressure now (gauge, in your unit) and Pressure now from Pressure the tyre was set to (gauge), Pressure unit and Temperature when it was set. The default figures on this page give pressure now (gauge, in your unit) of 31.45; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
5 steps
- Absolute pressure when set = 35 psi gauge + 14.696 psi ambient = 49.696 psi.
- Gas law at constant volume: absolute pressure scales with absolute temperature, 273.15 K / 294.15 K = 0.928608.
- Absolute pressure now = 46.148 psi; less 14.696 psi ambient gives 31.45 psi on the gauge.
- Around this pressure, 10 degrees F is worth 0.939 psi - the origin of the "1 psi per 10 F" rule.
- No placard pressure given, so no top-up figure is reported.
Its 4 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
4 sources
What the silca tire pressure calculator calculates
Corrects tyre pressure for temperature and altitude using the gas law on absolute pressure, and works out how much to add or let out to hit the placard pressure at the temperature you are actually inflating in.
How to use this silca tire pressure calculator
Enter Pressure the tyre was set to (gauge), Pressure unit, Temperature when it was set and Temperature now. Pressure now (gauge, in your unit) updates as you type, and “Use a worked example” loads checked figures you can adjust. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Pressure now (gauge, in your unit), Pressure now and Change from the set pressure.
The method follows Gay-Lussac’s law at constant volume: P/T is constant for absolute pressure and absolute temperature, FMVSS No. 110 (49 CFR 571.110), Tire selection and rims - the vehicle placard, NHTSA, Tire Safety: Everything Rides on It (DOT HS 809 361) and ICAO Standard Atmosphere (via the platform’s standard-atmosphere engine) for ambient pressure at altitude.
35 psi set at 21 C, checked at 0 C example
With Pressure the tyre was set to (gauge): 35, Pressure unit: psi, Temperature when it was set: 21, Temperature now: 0, the calculator returns Pressure now: 31.4520995. This example is checked against an independent source in the test suite.
What you can compare
Change one input at a time to see how it affects Pressure now (gauge, in your unit), Pressure now and Change from the set pressure. The inputs you can vary are Pressure the tyre was set to (gauge), Pressure unit, Temperature when it was set, Temperature now, Temperature unit and Placard (target) cold pressure.
Understanding Pressure now (gauge, in your unit), Pressure now and Change from the set pressure
The correct cold inflation pressure for a car, van or trailer is the vehicle manufacturer’s figure on the tyre information placard in the driver’s door opening (and in the owner’s manual), never the maximum pressure moulded on the sidewall. This tool only corrects a pressure you supply for temperature and altitude; it does not choose a pressure for you, and it does not model bicycle tyre pressure by rider weight.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
What information do I need for the silca tire pressure calculator?
You need Pressure the tyre was set to (gauge), Pressure unit, Temperature when it was set, Temperature now, Temperature unit, Placard (target) cold pressure, Altitude where the tyre is being checked and Altitude where the tyre was inflated. The page opens with default figures that give pressure now (gauge, in your unit) of 31.45, so you can see the scale before entering your own.
What does this silca tire pressure calculator show?
It shows Pressure now (gauge, in your unit), Pressure now, Change from the set pressure, Absolute pressure when set, Absolute pressure now, Sensitivity around this pressure, Add (+) or release (-) to reach the placard pressure and Ambient pressure at the checking altitude, with the working and any warnings for your entries.
Can I check how the silca tire pressure calculator result was calculated?
Yes. The “How this is worked out” section shows the calculation steps, and the sources section identifies the references used for the method.