Verify before flight. Check the POH/AFM for aircraft-specific limits and performance.
Performance
FPM to Climb Gradient Calculator
Convert vertical speed and groundspeed into climb gradient in ft/NM, percent grade, and climb angle for departure planning checks.
fpm
kt
Gradient—
Percent grade—
Climb angle—
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500 fpm at 90 knots
500 fpm at 90 kt means 500 / (90 / 60) = 333.3 ft/NM. At 120 kt, the same climb rate produces only 250 ft/NM.
A tailwind can reduce gradient over the ground even if the vertical-speed indicator remains at 500 fpm.
Formula and method
Climb gradient (ft/NM) = vertical speed (ft/min) ÷ groundspeed (NM/min).