Climb Gradient Calculator (ft/nm & %)
Convert climb rate and ground speed into the gradient obstacle charts speak — feet per nautical mile, percent and degrees, all consistent.
Rate (ft/min) is what the VSI shows; gradient (ft/nm) is what the mountain cares about. The conversion runs through ground speed — which is why a headwind steepens your gradient over the rocks without touching the VSI.
Formula
⚠️ For planning and education only. Weight & balance must be computed from YOUR aircraft's actual empty weight, arm and current equipment list, and verified against the POH/AFM envelope before flight.
Convert climb rate and ground speed into the gradient obstacle charts speak — feet per nautical mile, percent and degrees, all consistent.
About Climb Gradient Calculator (ft/nm & %)
Obstacles are positioned in miles, not minutes — so departure procedures publish required climb gradients in feet per nautical mile while your VSI stubbornly reports feet per minute. This converter bridges them through the variable that links time to distance: ground speed. Rate and GS in; gradient out in ft/nm, percent and degrees, mutually consistent and ready to compare against any chart's requirement.
How to use Climb Gradient Calculator (ft/nm & %)
- 1Enter — sensible defaults are pre-filled so you see a worked result immediately.
- 2Read the live results: .
- 3Check the "With your numbers" line to see the formula gradient (ft/nm) = ROC × 60 / GS; % = ft/nm ÷ 6076 × 100 substituted step by step.
- 4Adjust inputs (or flip the unit toggle) until the scenario matches yours, then copy or share the result.
Why use Climb Gradient Calculator (ft/nm & %)?
- ✓Instant, free and private — every calculation runs in your browser, nothing is uploaded
- ✓Built on the published formula gradient (ft/nm) = ROC × 60 / GS; % = ft/nm ÷ 6076 × 100 with sources cited on the page
- ✓Rate (ft/min) is what the VSI shows; gradient (ft/nm) is what the mountain cares about. The conversion runs through ground speed — which is why a headwind steepens your gradient over the rocks without touching the VSI.
- ✓Switch units, tweak any input and watch every result update live
Frequently asked questions
Why do charts use ft/nm instead of ft/min?+
Because terrain is geographic: a ridge 5 nm from the runway at 1,500 ft needs 300 ft/nm to outclimb regardless of how fast you fly. A rate requirement would have to assume your speed; a gradient requirement works for a 60-kt Cub and a 250-kt jet alike. Converting to your rate is the pilot's half of the contract — this tool's job.
What gradient do standard instrument departures assume?+
200 ft/nm unless charted otherwise — the TERPS default obstacle-clearance slope. At 90 kt ground speed that's exactly 300 ft/min; at 120 kt, 400 ft/min. Higher published gradients (e.g. 'minimum climb 425 ft/nm to 7,000') appear wherever terrain pierces the standard surface; meeting them is mandatory, not advisory.
Why does ground speed and not airspeed set the conversion?+
The gradient's denominator is distance over the ground. A 20-kt headwind at 90 kt TAS leaves 70 kt GS — the same 600 ft/min now covers each obstacle-laden mile in more time, banking more altitude per mile: 514 ft/nm instead of 400. Tailwinds steal gradient the same way, the classic trap departing downwind toward rising terrain.
How do the three output units relate?+
One slope, three dialects: 6,076 ft/nm would be 100% (45°). Typical light-single climbs run 300–500 ft/nm (5–8%, ~3–4.7°); a 200 ft/nm requirement is 3.3% or 1.9°. Percent suits runway-slope comparisons, degrees suit trigonometry, ft/nm suits charts — the tool keeps them locked together.
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