pounds per square inch to atmospheres

Bar, pascal, PSI — how much air is in your tires

The weather report gives pressure in hectopascals, the gauge on your pump has two scales — bar and PSI — and your car manual talks in bar. It is all one phenomenon wearing different uniforms. Here is how to read pressure without slipping up: why tires soften on their own in the cold, why a "3" on the dial can mean two wildly different things, and how much air really belongs in your wheel.