For your comfort and in order to preserve the lifetime of your mattress, do not over-inflate the mattress. When you are sitting on your inflated mattress, you should feel that the ground is close to your bottom. When you are lying on it, the air pressure should be distributed evenly beneath your body for optimal comfort. You can use a pump with a built-in pressure gauge like the Quechua 5.2 L: the recommended pressure is about 0.3 to 0.5 PSI.

Warning: the length may vary by more or less 10% depending on the air pressure inside the mattress.