Model Rocket Altitude Calculator
Enter launch-ready rocket and motor data to estimate how high the rocket will go above the pad. The result separates powered flight from coast and compares the estimate with an otherwise identical no-drag flight.
Estimated apogee (m)172.55
- Time to apogee (s)
- 6.15
- Burnout altitude (m)
- 52.76
- Burnout velocity (m/s)
- 63.04
- Coast altitude gained (m)
- 119.8
- Maximum velocity (m/s)
- 63.04
- No-drag apogee (m)
- 321.57
- Estimated altitude lost to drag
- 46.34%
Uses constant average thrust, a linearly falling mass, vertical windless flight, and a fixed drag coefficient.
Air density follows the NASA Glenn standard-atmosphere curve fit through 11,000 m absolute altitude.
How to use this calculator
- Weigh the complete launch-ready rocket, including the installed motor and recovery system.
- Copy total impulse, burn time, and propellant mass from the motor data or certification sheet.
- Measure the widest outside body diameter and enter a drag coefficient from a simulation or flight estimate when possible.
- Enter the launch-site elevation, then compare the drag-aware apogee with the no-drag result.
How the altitude estimate is calculated
This calculator models a rocket traveling straight up from the launch point. It converts grams and millimeters to SI units, then advances height and velocity in small time steps with fourth-order Runge–Kutta integration. The headline is the height above the launch point when upward velocity first reaches zero after burnout.
Let m0 be loaded mass, mp propellant mass, I total impulse, tb burn time, d body diameter, and Cd drag coefficient. The reference area is A = pi(d / 2)^2. Average thrust is T = I / tb. During the burn, mass falls as m(t) = m0 - mp(t / tb); after burnout it stays at m0 - mp.
At each step, the vertical acceleration is dv/dt = [T - mg - D] / m and height changes by dh/dt = v. The drag term is D = 0.5 rho Cd A v|v|, so it opposes the direction of travel. Density rho comes from the NASA Glenn standard-atmosphere curve fit at the launch elevation plus the simulated height. A second run sets D = 0; the displayed drag loss is 100(h_no_drag - h_drag) / h_no_drag.
What moves apogee most
Total impulse and loaded mass set the basic performance. For the same impulse, lowering launch-ready mass normally raises burnout velocity and apogee. Burn time also matters: a motor with the same impulse spread over more time has lower average thrust and spends longer working against gravity. Diameter and drag coefficient work together through frontal area, so a small change in diameter can have a noticeable effect because area changes with the square of diameter.
Elevation affects air density. A higher site has thinner standard air, which reduces modeled drag and can raise the result. This is only a standard-atmosphere correction, not a forecast for the launch day.
What this calculator leaves out
The model replaces a real thrust curve with constant average thrust and assumes propellant burns evenly. It assumes a vertical, windless flight with a constant drag coefficient; it does not model weathercocking, launch-rod or rail friction, angle of attack, compressibility, recovery deployment, or changing aerodynamic shape. It also stops if the drag-aware path reaches 11,000 m absolute altitude, the upper limit of the atmosphere curve used here.
Use a full flight simulator with a tested motor curve and current weather for launch planning. This calculator is an educational performance estimate, not a safety, motor-selection, or certification decision.
Worked example
With the default values—120 g loaded mass, 12 g propellant, 10 N·s total impulse over 1.6 s, 35 mm diameter, Cd 0.75, and sea-level elevation—the model estimates an apogee of 172.55 m. It reaches burnout at 52.76 m and 63.04 m/s, then gains another 119.80 m while coasting.
With drag removed, the same constant-thrust model reaches 321.57 m. The difference is an estimated 46.34% loss of altitude to drag; it is a comparison baseline, not an achievable flight result.
Common questions
Why does this estimate differ from OpenRocket?
OpenRocket can use a measured or certified thrust curve, detailed component geometry, stability, launch-guide settings, wind, and other flight inputs. This calculator uses one average thrust value, a constant drag coefficient, and a vertical path, so a difference is expected, especially with a strongly peaked motor curve or a complex rocket.
Where can I find total impulse, burn time, and propellant mass?
Look for the manufacturer data sheet, a certification listing, or the motor file used by your flight simulator. Use the published total impulse and burn time for the specific motor, and use propellant mass rather than the motor’s full loaded mass because the loaded rocket mass already includes the casing.
What drag coefficient should I use for a model rocket?
A flight-simulator estimate or a value inferred from actual flights is more useful than a generic number because drag coefficient depends on the rocket’s finish, fins, protuberances, speed, and angle of attack. If you do not have one, treat the result as a sensitivity check and compare several plausible values rather than relying on a single precise-looking answer.
Why is the no-drag altitude so much higher?
Drag rises with air density, frontal area, drag coefficient, and the square of speed. During the fast part of the ascent it removes kinetic energy that would otherwise carry the rocket through the coast, so the no-drag comparison is intentionally optimistic.
How does launch elevation affect apogee?
Higher elevation has lower standard-atmosphere density, which reduces the modeled aerodynamic drag and generally raises the calculated apogee. Actual temperature, pressure, humidity, and wind can depart enough from the standard atmosphere to change the real result.
Does motor delay time affect the altitude calculation?
No. Delay time begins after motor burnout and normally determines ejection timing, not the powered ascent or ideal apogee. It still matters for recovery: a deployment charge that fires too early or too late can damage a rocket or make recovery difficult.