Rate of Climb Calculator

How to use this calculator

1. Enter the Ground speed for the climb, in knots, km/h or mph.
2. Enter Climb gradient and set Gradient unit to feet per nautical mile (ft/NM), percent (%) or degrees (°).
3. Optionally enter Height to gain in feet or meters to add the time and distance rows.

Use the ground speed expected during the climb, which is the climbing true airspeed adjusted for wind, not the cruise speed and not the indicated airspeed. Check that the gradient unit matches the number: 300 ft/NM, 4.94% and 2.83° are the same slope, and choosing the wrong unit changes the answer many times over. An angle has to be less than 90°. A gradient that has to be met comes from the current official chart or procedure.

Formula

What the variables mean

rate of climb

vertical speed in feet per minute

gradient

height gained per horizontal distance over the ground

ground speed

speed over the ground in knots

60.7612

feet per nautical mile (6 076.12) divided by 100

Worked example

Reading the result

Required rate of climb is in ft/min with m/s beside it. The Gradient row restates your entry in all three forms, which confirms the unit was read as you meant. With a height entered, Time to gain that height and Ground distance covered follow from holding the rate and ground speed constant. Required describes what the gradient demands at that ground speed; it says nothing about what an aircraft can deliver. That comparison needs the climb performance in the flight manual for the actual weight, configuration and density altitude.

Assumptions and limitations

• Ground speed and gradient are constant for the whole climb.
• A percent gradient is height gained divided by horizontal distance, and an angle is converted with its tangent.
• The speed entered is horizontal speed over the ground, which for ordinary climb angles is very close to the speed along the flight path.
• The fall in climb performance with altitude is not modeled, so the time to gain a large height is optimistic for a real aircraft.
• Wind enters only through the ground speed you type and is assumed not to change with height.
• The calculator does not know the terrain, the procedure or the aircraft; it only relates three quantities.

Common mistakes

• Using indicated or true airspeed where ground speed belongs, which ignores a tailwind that raises the rate required.
• Entering a percent value with ft/NM selected: 1% is about 61 ft/NM, so the result is wrong by that factor.
• Reading the required rate as a rate the aircraft will achieve.
• Assuming a rate of climb seen near sea level will hold at a high, hot airfield.
• Measuring the height to gain from the wrong starting level, for example from sea level instead of from the airfield.
• Keeping the same target rate after the climb speed changes, when the rate required moves with ground speed.