How Do I Determine The Size Of My Frame On My Mtn Bike

Find yourself a tape measure. Measure (in inches) from the center of the bottom bracket (the axle thing that the pedal cranks spin around on) to the center of the top tube ot the seat binder bolt. This should get you very close.

You could also look on the seat tube for a sticker, lots of makers put a sticker there telling you what size the frame is.

Try posting this in General Cycling. You won't get lots of responses here. This is a forum for technical issues, not for actual discussions of cycling.