About this tool
The Rate of Descent & Glide-Slope Calculator turns a descent angle and ground speed into the feet-per-minute rate you need to fly, plus the descent gradient in feet per nautical mile and as a percentage. It has two modes: the standard 3° glide-slope shortcut and a custom angle. All calculations happen live in your browser.
For the standard 3° ILS glide-slope the tool uses the pilot rule of thumb rate of descent ≈ ground speed × 5, so 120 kt gives about 600 fpm. For any other angle it uses the exact relationship rate of descent = ground speed × tan(angle) × 101.27, where 101.27 = 6076.12 ÷ 60 converts nautical-mile geometry into feet per minute. The gradient is derived as rate × 60 ÷ ground speed, and the percentage is gradient ÷ 60.76.
Use the 3° mode for a quick approach cross-check and the custom mode for steep approaches, non-precision profiles or terrain-driven descent angles. Because ground speed drives the answer, remember that a tailwind raises the required rate and a headwind lowers it.