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.
- 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.
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.
Load / weight units: Choose pounds (lb) or kilograms (kg) for every weight shown.
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.
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.
Rim diameter: Type the wheel size, like 18 in 255/55R18.
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.
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.
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.
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, and 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.
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, so 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, since faster travel usually means less load or more air.
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, which is a clue that pressure is wrong.
Good tire care protects resale value too.