14 CFR §101.22

1. (a)Class 1—Model Rocket means an amateur rocket that:
   1. (1)Uses no more than 125 grams (4.4 ounces) of propellant;
   2. (2)Uses a slow-burning propellant;
   3. (3)Is made of paper, wood, or breakable plastic;
   4. (4)Contains no substantial metal parts; and
   5. (5)Weighs no more than 1,500 grams (53 ounces), including the propellant.
2. (b)Class 2—High-Power Rocket means an amateur rocket other than a model rocket that is propelled by a motor or motors having a combined total impulse of 40,960 Newton-seconds (9,208 pound-seconds) or less.
3. (c)Class 3—Advanced High-Power Rocket means an amateur rocket other than a model rocket or high-power rocket.