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Rocket Burn Time Calculator

Find how long a rocket engine can burn before it runs out of propellant.

How it is calculated

The tool divides the usable propellant by the rate at which the engine consumes it: t = mp ÷ ṁ. Here mp is the propellant mass in kg and ṁ is the mass flow rate in kg/s. The result is in seconds, and the tool also shows the same time in minutes (t ÷ 60). Both values have two decimals. Propellant mass and flow rate must both be above zero; zero or negative values give no result. The model assumes the engine runs at one steady flow rate from ignition until the tank is empty. It does not allow for a throttle schedule, a thrust ramp-up, or propellant left in the tank and lines, so real burn times are usually a little different.

Worked example

A stage holds 1800 kg of propellant and the engine uses 12.5 kg every second. Burn time in seconds: 1800 ÷ 12.5 = 144.00 s. In minutes: 144 ÷ 60 = 2.40, shown as 2.40 min. The tool displays 144.00 s and 2.40 min. If the flow rate were 8 kg/s instead, the same tank would last 225 s.

Try this example →

Common mistakes

  • Entering the flow rate per minute instead of per second. 750 kg per minute must be typed as 12.5 kg/s, otherwise the burn time is 60 times too short.
  • Using total launch mass instead of propellant mass. Only the fuel and oxidiser count, not the structure or payload.
  • Forgetting that the flow rate is the sum of fuel and oxidiser for a bipropellant engine. Using just the fuel flow makes the burn time too long.
  • Mixing pounds and kilograms. Both fields assume one mass unit, so a mix of the two gives a wrong time.
  • Treating the result as exact for a throttled engine. The tool assumes the flow stays the same for the whole burn.

About this calculator

A rocket engine’s burn time is simply its total propellant mass divided by its mass flow rate — the rate at which the engine consumes propellant, usually expressed in kilograms or pounds per second. A larger mass flow rate produces more thrust but empties the propellant tanks faster, so burn time is one of the core trade-offs engineers balance against thrust and specific impulse when sizing an engine for a given mission.

Aerospace engineers and propulsion designers use burn time calculations when selecting or designing a motor for a given vehicle, since it determines how long an engine can accelerate a rocket before staging or shutdown, and model rocketry hobbyists use the same math, scaled down, to match motor selection to a rocket’s flight profile and to predict apogee. It’s a foundational calculation that feeds directly into the rocket equation for estimating achievable velocity change (delta-v).

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