Rocket motors have letter designations based on their total impulse or power.
Small model rockets must weigh less than one pound at liftoff and carry less than 113 grams of propellant. They are typically thin cardboard tubes with plastic or balsa fins and nose cones. The smallest ones climb only a couple hundred feet, and can be built by children from kits. Small model rockets can be launched at community events in most metropolitan areas, and in any open field in some parts of the country. The motors typically use black powder for propellant.