Car Tire Pressure Calculator

Starting point:

The vehicle placard and owner manual remain the source of truth.

Vehicle class:

Placard cold pressure:

Front and rear may differ. Changing the unit preserves both physical pressures.

Front Rear

Curb weight:

Use curb weight rather than gross vehicle weight.

Passengers:

Average passenger weight:

Use a representative average for this trip.

Cargo weight:

Zero is valid for an unloaded trip.

Tire section width:

Front and rear may differ on staggered fitments.

Front Rear

Front axle share:

{{ front_share_percent }}%

Use 45%-65%; many front-engine passenger cars are near 55%.

Road surface:

Driving priority:

Tire setup:

Cold-soak temperature:

The forecast uses the planning rule of roughly 1 psi per 10 deg F.

Current Next

Current cold readings:

Leave both at zero for target-only guidance.

FrontRear

Known pressure ceilings:

Use the lowest applicable tire, wheel, or vehicle limit; zero is neutral.

FrontRear

Axle	Load	Baseline	Target	Action	Next cold	Working window	Copy
{{ row.axle }}	{{ row.load }}	{{ row.baseline }}	{{ row.target }}	{{ row.action }}	{{ row.forecast }}	{{ row.window }}

Before adjusting pressure

Calculation basis

Target = clamp(baseline x setup factors x width factor + axle-load delta / 45 kg)

This is a repo-authored planning heuristic. The vehicle label, owner manual, tire load table, and the lowest applicable equipment limit take priority.

Correct tire pressure starts with the vehicle manufacturer's cold-pressure recommendation, usually printed on the driver-door placard and repeated in the owner's manual. The maximum pressure molded into a tire sidewall is an equipment limit, not the normal inflation target for the vehicle.

A cold reading is taken before driving has warmed the tires, commonly after the vehicle has been parked for at least three hours. Front and rear recommendations may differ because the axles carry different loads. Cargo, passengers, towing, replacement tires, and sustained high-speed use can require instructions beyond the everyday placard value.

Placard pressure: The manufacturer's recommended cold pressure for the specified tire and vehicle loading conditions.
Current cold reading: A gauge measurement taken before driving heats the tire.
Pressure ceiling: The lowest applicable vehicle, wheel, or tire limit; it must never be treated as a target by itself.

Air pressure changes with temperature. A rough planning rule is about 1 psi for each 10°F change in cold-soak temperature, but real tires do not follow that shortcut perfectly. Recheck with a gauge when conditions change instead of adding or bleeding air solely from a forecast.

Pressure affects load capacity, heat, braking, handling, tire wear, and fuel or energy use. A computed adjustment can help plan a check, but it cannot replace the placard, a tire load-and-inflation table, or qualified advice for towing, heavy loads, altered fitments, or track use.

How to Use This Tool:

Use the door placard whenever it is available; a vehicle-class preset is only a temporary planning fallback.

Choose Door placard and enter the front and rear cold pressures with the printed unit. Use Vehicle class preset only until the actual label or manual can be checked.
Enter curb weight, every occupant including the driver, cargo, tire section widths, and the estimated front-axle share for the trip.
Select the road surface, driving priority, and tire setup that best describe the plan. These apply small heuristic adjustments and do not override manufacturer limits.
Compare current and forecast cold-soak temperatures. Enter optional current cold readings to receive add, bleed, or hold guidance.
Add known pressure ceilings only when they come from the vehicle, wheel, or tire documentation. Review Pressure plan and stop if a target reaches the displayed working minimum or maximum.

Interpreting Results:

Front target and Rear target are heuristic cold-pressure targets constrained by the active working window. When current readings are supplied, the action is the target minus the reading: positive means add air, negative means bleed air, and a difference below 0.25 psi is shown as hold.

The displayed target band extends 5% around the target or 1.5 psi, whichever is larger, then stops at the working limits.
A Boundary active warning means at least one target was clamped. Do not keep adding or removing air to chase an unconstrained model result.
The temperature forecast is an approximation from the current reading when one exists, otherwise from the target. Confirm the actual cold reading before driving.
The tire-pressure monitoring system reference at 75% of placard pressure is a warning threshold, not a safe inflation recommendation. Inflate to the vehicle guidance before relying on the warning lamp.

Technical Details:

The model normalizes mass to kilograms, width to millimetres, pressure to psi, and temperature to degrees Fahrenheit. Front and rear axle loads are the loaded vehicle mass multiplied by the selected axle shares.

Formula Core

Loaded vehicle mass includes curb weight, every passenger at the entered average, and cargo.

M_{loaded} = M_{curb} + N \times M_{person} + M_{cargo}

For each axle, the unconstrained target starts with baseline pressure, multiplies the selected surface, priority, setup, and width factors, then adds 1 psi for every 45 kg by which axle load differs from its baseline load.

P_{raw} = \max (18, P_{base} \times f_{surface} \times f_{priority} \times f_{setup} \times f_{width} + \frac{M_{axle} - M_{baseline axle}}{45})

Placard mode fixes the width factor at 1 and uses the selected axle share for both current and baseline loads. Its baseline mass is curb mass plus one average passenger. Preset mode uses 235 divided by tire width in millimetres and a fixed 55% front, 45% rear baseline split at the class reference mass.

Surface, priority, and tire setup factors
Group	Choice	Factor
Surface	Highway / steady	1.02
Surface	City / mixed	1.00
Surface	Rough roads	0.97
Surface	Winter / cold	1.01
Priority	Comfort	0.97
Priority	Balanced	1.00
Priority	Fuel / EV efficiency	1.02
Priority	Handling / high-speed	1.04
Tire setup	All-season standard load	1.00
Tire setup	Summer / performance	1.01
Tire setup	Winter	1.02
Tire setup	XL / reinforced	1.04

Lookup Core

Class presets provide fallback baselines, reference masses, and working windows. They are not vehicle specifications.

Vehicle class fallback pressure values
Class	Reference mass	Base front / rear	Minimum front / rear	Maximum front / rear
Compact / hatchback	1,300 kg	32 / 32 psi	29 / 29 psi	41 / 41 psi
Sedan	1,500 kg	33 / 33 psi	29 / 29 psi	42 / 42 psi
Wagon / CUV	1,700 kg	34 / 36 psi	30 / 31 psi	43 / 44 psi
SUV	1,900 kg	35 / 37 psi	31 / 32 psi	44 / 45 psi
Pickup, light load	2,100 kg	36 / 40 psi	32 / 34 psi	44 / 48 psi
EV / performance	2,000 kg	38 / 40 psi	32 / 34 psi	45 / 46 psi

Rule Core

Placard-mode minimum is the greater of 20 psi and 6 psi below baseline. Its maximum is 7 psi above baseline, or 8 psi above when handling priority or XL tires are selected. A supplied equipment ceiling can only lower that maximum. The final target is the raw pressure clamped inside this window. Preset mode uses the minimum and maximum in the class table.

Temperature shift is the forecast cold-soak temperature minus the current cold-soak temperature, divided by 10°F per psi.

P_{forecast} = P_{starting} + \frac{T_{forecast} - T_{current}}{10}

Conversions use 1 lb = 0.45359237 kg, 1 in = 25.4 mm, 1 psi = 6.894757293 kPa, and 1 psi = 0.06894757293 bar.

Safety Limitations:

The pressure model is a planning heuristic, not a manufacturer load-and-inflation table. The vehicle placard and owner manual take priority whenever they conflict with a result.

Do not use the tire sidewall maximum as the normal target or exceed the lowest vehicle, wheel, or tire limit.
Vehicle-class presets cannot account for exact axle ratings, tire construction, load index, speed rating, towing instructions, or modified suspension and fitment.
Check pressure with an accurate gauge when tires are cold. Inspect damage, unusual wear, repeated pressure loss, and valve condition separately.
Use manufacturer or qualified tire guidance for towing, maximum payload, high-speed driving, track use, nonstandard tires, or a persistent warning lamp.

Worked Example:

Cold check before a temperature drop

A placard specifies 33 psi front and rear. With the neutral city, balanced, and all-season choices and no load change from baseline, both targets remain 33 psi. Current cold readings of 30 psi front and 34 psi rear produce actions to add 3 psi at the front and bleed 1 psi at the rear. A drop from 20°C to 5°C is 27°F, so the rough forecast subtracts 2.7 psi. The tires still need a real cold-gauge check after the weather changes.

References:

Tire Safety Ratings and Awareness, National Highway Traffic Safety Administration.
Federal Motor Vehicle Safety Standard No. 138, Tire Pressure Monitoring Systems, National Highway Traffic Safety Administration.