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Specific Impulse Calculator
Calculate a rocket engine’s specific impulse (Isp), a standard measure of how efficiently it uses propellant.
N
kg/s
What specific impulse measures
Specific impulse (Isp) measures how efficiently a rocket or jet engine converts propellant into thrust — a higher Isp means more thrust (or longer burn time) for the same amount of propellant.
The formula
Effective exhaust velocity Ve = F / ṁ, where F is thrust and ṁ is the propellant mass flow rate. Specific impulse expressed in seconds is Isp = Ve / g0, where g0 is standard gravitational acceleration (9.80665 m/s²), used as a conversion constant by convention even for engines operating in space.
This is the standard rocket propulsion formula for specific impulse, used across aerospace engineering references.
Last reviewed August 2026