Total impulse is the area under the thrust–time curve, computed here by the trapezium rule over your samples. It is the motor's total push, in newton-seconds, and it sets the impulse class. Classes are a geometric ladder: A is 2.5 N·s, and each letter doubles it — B 5, C 10, D 20, E 40, F 80, G 160, H 320, I 640, J 1,280, K 2,560, L 5,120, M 10,240, N 20,480, O 40,960. The half classes at the bottom are 1/4A (0.625 N·s) and 1/2A (1.25 N·s). A motor must not exceed its class ceiling; the certificate lists the measured value, not the label.

Burn time here runs from the first sample above 0.5% of peak thrust to the last one, so leading and trailing zeroes do not inflate it. That is a curve-processing convention, not the motor certification's definition: certification bodies measure burn time from ignition to the point thrust falls below a threshold, and some motors have a long low tail that changes the number. Use the manufacturer's data for a certification claim.

Average thrust is total impulse divided by burn time. It is the number in a motor designation such as C6-5, but it says nothing about the shape. A motor with a sharp initial spike can average 6 N and still fail to lift a heavy rocket after the first 0.2 s. The peak tells you about the airframe and launch lug; the average plus the mass tells you about liftoff. A common club rule is at least 5:1 average thrust to weight at liftoff, with enough thrust at every point of the burn that the rocket keeps accelerating.

Data sources. Motor manufacturers publish .eng (RASP) or .rse (RockSim) files containing thrust samples; test stands and altimeters produce their own curves. A curve from a different propellant lot, temperature or nozzle is not the curve in your rocket. The sample shipped with this tool is illustrative and must not be used for a flight decision.

Last reviewed: 2026-10-19. A motor-analysis aid, not a certification or flight-safety determination.