Check A Bike Pedal
Step 3 of 3: Replace A Bike Pedal
If the bike pedals are single sided you can tell which is left and right. Double sided pedals are marked - either on the flat end of the axle or beside the 15mm flats for screwing them on. Modern pedals are always marked 'R' and 'L'. Older French or Italian pedals may be marked 'D' and 'G' or 'D' and 'S'. The material of the pedal axle is usually harder than the material of the crank so take care as it's easy to damage the soft thread of the crank.
Spin the bike pedal by hand. It should spin freely for a few turns before is slows down and stops.
If you pull the bike pedal sideways there should be no discernible play.