Pressure and temperature are directly related. That means that as the temperature goes up for a sample of air, so does the pressure. This is because as the temperature rises, the molecules have more kinetic energy. Another way to say this is that they are moving faster. As they move, they come into contact with each other more often, creating greater pressure.
Use the sliders to see how temperature affects pressure in the box below.
100°F
30PSI
A good estimate to use when comparing tire pressure to air temperature is for every 10°F, tire pressure will adjust by 1 PSI (Source:TireBuyer).