OR...

Flick the tire with your finger it the sound should be close to a "ping" rather than a "thunk", if you're unsure, have your local LBS check for correct pressure and then see how it sounds

Pinch the tire with your fingers, you should "just" be able to depress the sidewalls slightly. ( You want the tires "hard" AND a bit pliant).

Get a foot pump with combination prsta/schrader head equipped with a built in pressure gauge

Ride Inflated
Pat