What pressure should a tire have? I am a new bike rider.

Over three months, my wheels are a little bit flat. However I am not too sure as to what pressure I should pump them back up to. Currently they show 25 PSI (172 kPa). It is a hybrid bike I use to ride to work.

Is there any way I can check what the pressure should be? And what is the lowest acceptable pressure that is ok for tires?
Each type and size of tire has a different pressure range. The range is written or embossed right on the side of the tire.

The actual pressure you choose is dependent on what you are using the bike for, the road surface you ride on and your general preference. A safe choice the middle of the specified pressure range.

Lower pressure will give a bit more comfort, higher pressure gives slightly less rolling resistance. Beware that too low pressure can make the inner tube susceptible to punctures caused by hitting a bump hard (known as 'pinch flats').