what is the smallest you could make a jump to start doing tricks on

Give me some insight on your experience and skill riding dirt bikes... Have you every raced before?, what kind of dirt bike are you wanting to attempt these ''tricks'' on?

You have to give more information than what your asking.

It all depends on what kind of trick you want to do. On smaller jumps, you will not have enough air time to do any major whips or stuff like that, but you may be able to do a no hander, or something simple like that..

l am a long time MX racer but not an FMX rider. Based on my limited knowledge l would think you'd need a pretty big ramp to pull any major tricks. l always assumed the FMX guys practiced their stunts over a foam pit but l could be wrong.Barry M???

Depends on the size of the bike, experience of the rider, type of trick, and things on that sort.
More details please.

l started doing tricks when l was getting about 1 metre in the air it depends on what tricks you want to do you can do no handers, no footers and look backs and small tricks like that with about 1 metre.