Rate of Climb Calculator

Rate of climb depends on excess power: the difference between power available (from the engine and propeller) and power required (to maintain level flight). The formula is ROC = (excess power x 33,000) / aircraft weight, where power is in horsepower and weight in pounds. Higher altitude, higher temperature, and greater weight all reduce excess power and therefore rate of climb.

Vy is the best rate-of-climb speed, giving the most altitude gain per unit of time (highest vertical speed in feet per minute). Vx is the best angle-of-climb speed, giving the most altitude gain per unit of horizontal distance, useful for clearing obstacles after takeoff. Vy results in a shallower climb angle but reaches altitude faster. Both are published in the POH.

As density altitude increases, both engine power output and propeller efficiency decrease because the air is less dense. The result is a significant reduction in excess power and therefore in rate of climb. At the aircraft's absolute ceiling, rate of climb approaches zero. Service ceiling is defined as the density altitude at which rate of climb equals 100 feet per minute.

Climb gradient is the vertical distance gained per 100 feet of horizontal distance traveled, expressed as a percentage. Climb gradient (%) = (ROC / TAS) x (60 / 101.27). Alternatively, gradient = tan(climb angle) x 100. TERPS obstacle clearance requirements use gradient in feet per nautical mile: gradient (ft/nm) = ROC (fpm) / TAS (knots) x 60.

A simple approximation for time to reach an altitude is: time = altitude gain / average rate of climb. Since rate of climb decreases with altitude, average ROC is approximately (ROC at takeoff + ROC at cruise altitude) / 2. For more accurate estimates, use the POH climb table which gives cumulative time, distance, and fuel to altitude checkpoints.