A temperature-only model.

Top-view schematic of four tire positions alongside steps to copy specifications, use a gauge, record conditions and compare appropriately.
Original measurement-plan illustration. Each tire has its own entry; the spare is checked separately if fitted. A matching number is not a tire-condition inspection.

For a fixed amount of gas in a fixed volume, absolute pressure is proportional to absolute temperature. We use the NASA-described ideal-gas relationship to estimate a temperature change:

P₂ = (P₁ + Pₐₜₘ) × T₂ ÷ T₁ − Pₐₜₘ

P₁ and P₂ are gauge pressures; temperature is in kelvin. The model assumes the starting rested tire is set to the entered vehicle placard pressure. It also assumes no air loss, fixed volume and constant standard atmospheric pressure. Ambient temperatures stand in for tire-air temperatures only after equilibrium.

Driving heat, sun, changing altitude, tire deformation and leaks can change a real reading. We have not measured a tire-specific error range. This model does not return a new recommended inflation target or determine a cause of pressure loss.

Units and input limits.

NIST gives 1 atmosphere as 101.325 kPa, approximately 14.6959 psi. We use 1 psi ≈ 6.894757 kPa and 1 bar = 100 kPa. Celsius converts to kelvin by adding 273.15; Fahrenheit first converts to Celsius.

The calculator supports starting values from 10 to 120 psi equivalent and ambient temperatures from −100°F to 180°F. These are software input bounds, not an assertion that a particular tire or vehicle should operate anywhere in that range. Model combinations producing zero or negative gauge pressure are rejected as outside this tire tool’s useful range.

Results are rounded for display: psi to one decimal, bar to two, kPa to whole numbers. Unit switching therefore introduces small display-rounding differences; the example values are not vehicle recommendations.

Altitude and load need their own references.

Gauge pressure is relative to the surrounding atmosphere. This model holds atmospheric pressure constant, so it does not predict a route with changing altitude. It also holds gas amount and volume fixed; it does not calculate a pressure from vehicle weight, tire size or towing load. Use the relevant vehicle and tire instructions for that configuration.

Find the applicable specification before comparing numbers. Extra PSI is not permission to exceed vehicle or tire load limits.

How we use evidence.

Search suggestions and public discussions help identify questions. They do not establish safety rules or search volume. Guides link the primary sources behind their important claims. Official guidance is interpreted for the specific conditions it describes, with your vehicle manual as the vehicle-specific reference.

This site uses NHTSA’s three-hour cold-tire definition for consistent U.S.-oriented guidance. Manufacturer instructions may specify other conditions. We do not combine different warm-inflation rules into a universal compensation number.

The check sheet reports arithmetic comparisons only for readings you mark as cold. It does not infer a leak, tire health or roadworthiness. There is no sensor scan, vehicle database or service inspection.

Questions from community discussions.

These public Reddit threads helped identify situations to explain. The question summaries below are paraphrases, not verified advice or a representative user survey. Comments may conflict. Use the primary sources and vehicle instructions for actions.

Reddit may require sign-in or a security verification before showing a discussion. The summaries below remain problem context, not verified advice.

Search suggestions tell us that an expression appeared; they do not establish search volume, popularity rank or a recommended action. The site does not host a forum or reproduce community answers as safety rules.

Primary sources

Primary sources checked November 5, 2026. This is not a vehicle-specific inspection.

Your entries and optional local records.

Calculator and check-sheet inputs are processed in your browser and are not sent by these tools to a server. There is no account, location request, analytics script, cookie-based tracking or automatic saving of entries. Your hosting provider can still receive ordinary page requests.

Refreshing or clearing the current sheet removes its unsaved entries. If you explicitly choose Save this check locally, reviewed entries, dates and notes are stored on this browser (up to 50 checks). They are not uploaded by these tools. Clear saved checks deletes that history; clearing the current sheet does not. Browser site-data deletion or a different device can remove access. Downloaded CSVs and PDFs remain separate files you control. The print action opens your browser’s print dialog; where supported, you can save a PDF. No report is automatically uploaded. Shared scenario links contain only the visible example or calculator parameters.