Introduction
This Tire Pressure Calculator tells you how much air your tires need. It uses real load and inflation math, not guesses. Put in your tire size, load index, and door jamb pressure, and it gives you the right cold pressure in PSI, bar, or kPa.
The tool has three modes:
- OEM → Replacement Match: Put in your stock tire and your new tire. The calculator finds the pressure that keeps the same load support. It also checks tire diameter change and speedometer error. To compare two sizes side by side first, try the Tire Size Calculator or the Tire Comparison Calculator.
- Load & Terrain Optimizer: Enter your front and rear axle weights and pick your terrain. You get a front and rear pressure for pavement, gravel, rocks, sand, or snow.
- Specialty Tire Lookup: Search farm, implement, and commercial truck tires by size, name, or catalog number. Then see the load and inflation table for single, dual, or triple wheels.
Every answer comes with a step-by-step solution and a chart, so you can see how the number was found. There is also a temperature tool, because tires lose about 1 PSI for every 10 °F drop in air temperature.
Right pressure means better grip, longer tire life, and better gas mileage. Always check your tires when they are cold, and never go over the max pressure on the sidewall. If you want to see what correct pressure does for your fuel bill, check the Gas Mileage Calculator and the Fuel Cost Calculator.
How to use our Tire Pressure Calculator
Enter your tire sizes, load ratings, and the weight your tires carry. The calculator gives you the right cold inflation pressure in PSI, bar, or kPa, plus load capacity, step-by-step math, and a load-versus-pressure chart.
Pick a tab: Use OEM → Replacement Match to set pressure for a new tire size, Load & Terrain Optimizer to set pressure from real axle weights, or Specialty Tire Lookup for ag, truck, and implement tires.
Pressure units: Choose PSI, Bar, or kPa. All pressure results show in this unit. For other unit swaps, the Unit Converter Calculator covers length, mass, and volume.
Load / weight units: Choose pounds (lb) or kilograms (kg) for every weight shown. See the Pounds to Kilograms Calculator if you need to convert a scale ticket.
OEM → Replacement Match
Tire type: Pick Metric, P-Metric, LT Metric, or LT High Flotation for the old tire and the new tire. High Flotation tires ask for a diameter instead of an aspect ratio.
Section width: Type the first number in the tire size, like 255 in 255/55R18. Pick mm, cm, or in. The Tire Conversion Calculator helps if your size is written in inches.
Aspect ratio (%): Type the second number in the size, like 55 in 255/55R18.
Overall diameter: For High Flotation tires, type the tire's full height, like 31 in 31X10.50R15LT. The Tire Height Calculator works this out from a metric size.
Rim diameter: Type the wheel size, like 18 in 255/55R18. When fitting new wheels, also check the Wheel Offset Calculator and the Bolt Circle Calculator.
Load index: Type the number right after the size on the sidewall, from 60 to 130. For LT tires use the first number.
Load range / service: Pick SL or XL for metric tires, or Load Range B through F for LT tires. This sets the tire's rated pressure.
Door jamb (placard) pressure: Type the pressure on your driver's door sticker. Do not use the sidewall max.
Load & Terrain Optimizer
Max load rating per tire: Type the "Max Load" number from your tire sidewall.
Max pressure: Type the "Max Press" number from your tire sidewall.
Front axle weight: Type the weight on your front axle, from a scale if you have one.
Rear axle weight: Type the weight on your rear axle.
Terrain condition: Slide from Pavement to Sand/Snow. Softer ground means a bigger pressure drop for grip and float.
Specialty Tire Lookup
Product name, size, or catalog number: Type a size like 480/80R42, a name, or a catalog number, then press Look up.
Matched tire: Pick the exact tire from the list of matches.
Load carried per tire: Type the weight each tire in that spot must hold. For freight loads, the Volumetric Weight Calculator and Freight Density Calculator can help you estimate cargo weight.
Speed rating column: Pick MPH or KPH to match your load table.
Axle configuration: Pick Single, Dual, or Triple for how many tires share that axle spot.
Temperature adjustment
Temperature change: Pick how many degrees the air temperature moves, in °F or °C. The tool shows how much your tire pressure will rise or fall. Switch between scales with the Fahrenheit to Celsius Calculator.
Tire Pressure: What It Is and Why It Matters
Tire pressure is the amount of air inside a tire. It is measured in PSI (pounds per square inch), bar, or kPa. Air, not rubber, holds up your vehicle. The right pressure lets each tire carry its share of the weight in a safe way.
Where to Find the Right Number
Your correct cold tire pressure is on a sticker inside the driver's door jamb, or in the owner's manual. This is called the placard pressure. The big number on the tire's sidewall is different — that is the maximum pressure the tire can hold, not the pressure you should run every day.
Load and Pressure Work Together
Every tire has a load index and a load range (like SL, XL, or LT ranges B through F). These tell you how much weight the tire can carry and at what pressure. More air means more load capacity, up to the tire's limit. That is why heavy trucks and tractors run higher pressures than small cars.
When you switch to a new tire size or a different load range, the old placard number may no longer be right. You need the pressure that gives the new tire the same load capacity your vehicle was built for. Bigger, heavier tires also change how the vehicle pulls away — see the Power to Weight Ratio Calculator and the Gear Ratio Calculator.
Too Low or Too High
- Underinflated: the tire flexes too much, gets hot, wears out at the edges, and can fail. It also uses more fuel — the Fuel Consumption Calculator shows the cost over a year.
- Overinflated: the ride is harsh, grip drops, the center of the tread wears fast, and bumps can damage the tire.
Temperature Changes Pressure
Air shrinks when it gets cold. Pressure drops about 1 PSI for every 10 °F (about 6 °C) the outside air falls. That is why a TPMS light often comes on during the first cold morning of fall. Always check pressure when the tires are cold — before driving, or at least three hours after. The physics behind this is the same gas behavior shown in the Ideal Gas Law Calculator, and cold snaps can be judged with the Wind Chill Calculator.
Airing Down Off-Road
On sand, snow, mud, or rocks, drivers sometimes lower pressure on purpose. A softer tire spreads out, so it floats better and grips more. This only works at slow speeds. Low pressure on pavement is dangerous and can pop the tire off the wheel. Air back up before you drive on the road again. Bicycles follow their own rules — use the Bike Tire Pressure Calculator for those.
Farm, Truck, and Specialty Tires
Ag tractor tires, implement tires, and commercial truck tires use printed load and inflation tables from groups like TRA and ETRTO. You look up the load on each tire, then read the lowest pressure that carries it. Duals and triples share the load, so each tire in the set is rated a bit lower than a single. Speed matters too — faster travel usually means less load or more air. Fleet operators can pair this with the Freight Class Calculator and the Mileage Calculator.
Simple Habits
- Check all four tires, plus the spare, once a month.
- Use your own gauge; gas station gauges are often off.
- Set pressure when tires are cold.
- Never go above the sidewall maximum.
- Look for uneven tread wear — it is a clue that pressure is wrong.
Good tire care protects resale value too. See what your vehicle is worth with the Car Value Calculator or the Car Depreciation Calculator.