How to Check Tire Pressure: Cold, With a Gauge

Five minutes, once a month

Checking tire pressure takes one gauge, one sticker and five minutes. Doing it at the wrong time, or against the wrong number, makes the reading useless.

NHTSA's guidance is simple: check the pressure in all four tires and the spare at least once a month, when the tires are cold. Here's what that means, what to use, and the steps.

When to check: cold means parked for three hours

NHTSA defines a cold tire as one that hasn't been driven for at least three hours. The pressure your vehicle maker recommends is a cold pressure, so that's the only reading you can compare against it.

Driving warms the tires, and warm air pushes harder. A tire checked right after a run down I-595 reads higher than the same tire did that morning, even though it holds the same air.

The easy routine:

• First thing in the morning, before the car moves.
• Or after it's been parked in the shade for a few hours.
• Not right after a drive, unless you have no choice. More on that below.

What to check with: pick a gauge

Don't rely on the gauge built into a gas station air hose. Tire makers' guides recommend using your own gauge: check with it, add air with the station's hose, then check again with your gauge.

Three common types:

Any of them works if it seals on the valve and you read it carefully. Keep it in the glove box so it's there when you need it.

And your TPMS light? It isn't a gauge. Under the federal standard, FMVSS No. 138, the warning has to come on once a tire is 25 percent or more below the placard pressure. A tire can be well under the right number with the light still off. Our TPMS light guide covers what the light does and doesn't tell you.

Where to find your number: the door placard

Your target pressure is printed on the Tire and Loading Information label. NHTSA says it's on the driver's side door edge or door post (the B-pillar) and in the owner's manual. On a vehicle without a B-pillar, look at the rear edge of the driver's door.

A few things to read on that label:

• Front and rear. Some vehicles list different pressures for each axle.
• The spare. A compact spare often has its own pressure.
• The tire size. The label assumes the size your vehicle maker fitted. If you're running a different size or load type, ask your installer what pressure to use.

The same sticker lists your original tire size, which is how our Tire Size Finder reads it.

Not the number on the tire

The tire's sidewall has a pressure on it too, usually after "Max. Press." USTMA explains that this is the maximum the tire is built to hold, whatever vehicle it's on. It isn't your target. Our post on why not to inflate to the sidewall max goes into why the two numbers differ.

How to check tire pressure, step by step

1. Read the placard and note the cold pressure for the front, the rear and the spare.
2. Start with cold tires, parked for at least three hours.
3. Unscrew the valve cap and put it somewhere you won't lose it.
4. Press the gauge straight onto the valve stem, firmly, until the hiss stops. A hiss that keeps going means it isn't sealed.
5. Read the number. If it looks off, take the reading again.
6. Compare it to the placard for that position.
7. If it's low, add air in short bursts and recheck with your gauge after each one.
8. If it's high on a cold tire, let a little out by pressing the pin in the center of the valve, then recheck.
9. Put the cap back on before you move to the next tire.
10. Repeat on every tire, spare included.

Write the readings down. A tire that's lower than the others month after month is telling you something.

Checking at the gas station after a drive

Sometimes the air machine is the only chance you get, and the tires are warm. Two rules:

• Don't let air out of a warm tire to match the placard. NHTSA's summer guidance is not to bleed warm tires. The pressure drops as they cool, and a tire set to the placard while warm sits below it once it's cold.
• If a warm tire reads below the placard, it's low. Add air to bring it up, then recheck the next morning, cold, and adjust.

Florida heat and the reading

South Florida makes cold checks harder: the car is warm by mid-morning, and the air in an A/C garage and on a sunny driveway can be very different temperatures. Pressure moves with the air temperature, about 1 to 2 psi for every 10°F by the tire industry's rule of thumb. Our pressure and temperature guide explains the math, and the calculator below estimates how much a reading should move:

The takeaway: a hot afternoon can make a low tire read normal. Check early, and check monthly. Our guide to Florida heat and tires covers why pressure matters even more in the heat.

When the gauge says more than "add air"

A tire that loses a few psi between monthly checks, along with the other three, is normal. These aren't:

• One tire that keeps reading lower than the rest
• a tire that needs air every week
• a TPMS light that comes back right after you've set all four

Those point to a leak: a nail, a valve stem or a bead that isn't sealing. While the gauge is out, check the tread too; our guide on how to check tread depth takes two more minutes. Then run your readings through Do I Need Tires Yet?.

Driving for a living? Our post on tires for Uber and Lyft drivers shows what low pressure costs in fuel over a high-mileage year.

If a tire won't hold air, Extreme Tires repairs punctures after taking the tire off the wheel to inspect it, at the Sunrise shop or by mobile van in Miami-Dade, Broward and Palm Beach. If it's time for new ones, shop tires by size; free shipping covers the 48 contiguous states and DC, and installation in South Florida is either ship-to-store in Sunrise or the mobile van. See how installation works, or call (954) 773-1896.