Tire pressures are quoted for cold tires and will be specified in your vehicle handbook and may be on a sticker inside the fuel flat, on the drivers (or passengers) door or even inside the glove box.
Normally there are two tire pressures quoted; one for "normal use" and a higher tire pressure for when the vehicle is underload. Make sure you adjust your tyre pressures accordingly.
If you don't know the correct tyre pressure for you vehicle, refer to the manufacturer's customer service department.
Never use the tire pressure quoted on the tyre sidewall. This pressure refers to the maximum inflation pressure a tyre can contain under maximum load.