Top of Descent Calculator
Use the 3-to-1 rule to find where to begin your descent and the rate of descent needed to hold a 3° path.
Formula
Distance (NM) = altitude to lose (in thousands of feet) × 3. Rate of descent ≈ ground speed × 5 ft/min for a 3° path. Add distance to slow down if needed.
FAQ
What is the 3:1 rule?
Plan 3 nautical miles of track for every 1,000 ft of altitude to lose, which gives roughly a 3° descent path.