Descent Rate & Top of Descent Calculator
Start down about 3 NM for every 1,000 ft to lose and fly a descent rate of roughly ground speed × 5 ft/min, so 120 kt on a 3° path needs about 600 ft/min.
For general informational use. Verify critical aviation calculations and weather with an authoritative source.
Rate of descent for a 3° path
A 3° glidepath loses about 318 ft per nautical mile. The required vertical speed is therefore groundspeed × 5.3 ft/min. Pilots often use groundspeed × 5, which is easy to remember but about 6% too low.
| Groundspeed | Exact 3° rate | Groundspeed × 5 |
|---|---|---|
| 90 kt | 478 ft/min | 450 ft/min |
| 120 kt | 637 ft/min | 600 ft/min |
| 150 kt | 796 ft/min | 750 ft/min |
| 250 kt | 1,327 ft/min | 1,250 ft/min |
| 300 kt | 1,592 ft/min | 1,500 ft/min |
| 450 kt | 2,388 ft/min | 2,250 ft/min |
The 3-to-1 rule for top of descent
For a 3° descent, start down about 3 NM for every 1,000 ft you need to lose. Descending from FL350 to a 5,000 ft fix means losing 30,000 ft, so start about 90 NM before the fix. Add about 1 NM per 10 kt of tailwind and a few miles for slowing down, which jets usually need in level flight before the approach.
Light aircraft: plan for comfort
For piston aircraft without pressurisation, many pilots plan around 500 ft/min for passenger comfort. At 120 kt groundspeed that is a path of about 2.4°, so start down about 4 NM per 1,000 ft rather than 3.
Groundspeed, not airspeed
The rate depends on how fast you cover the ground. With a 30 kt headwind on approach, a 120 kt aircraft needs only about 480 ft/min; with a 30 kt tailwind it needs about 800 ft/min. Use the GPS groundspeed and adjust as the wind changes during the descent.
Common mistakes
- Planning the descent with cruise TAS and forgetting the slower groundspeed lower down.
- Using the altitude to lose to the airport instead of to the first fix or the circuit height.
- Forgetting the speed reduction phase in faster aircraft, which can need 10 NM or more.
The 3-to-1 rule and the 3° path
A 3° descent path is the standard for instrument approaches and a comfortable profile for most aircraft. It works out to about 3 nautical miles of distance for every 1,000 ft you need to lose, and a vertical speed of roughly five times your ground speed.
How to use it
- Enter your current altitude and the altitude you need to reach.
- Enter expected ground speed during the descent.
- Keep 3° or enter a shallower or steeper angle.
- Read top-of-descent distance, required vertical speed and time to descend.
Method and calculation
Distance (NM) = altitude to lose ÷ (tan(angle) × 6,076 ft). Rate of descent (ft/min) = ground speed (kt) × 101.27 × tan(angle). Time = altitude to lose ÷ rate of descent. The 3:1 rule (3 NM per 1,000 ft) and the 5 × ground speed rule are shown as quick cross-checks.
Worked example and practical notes
Descending from 9,500 ft to 2,000 ft (7,500 ft to lose) at 140 kt on a 3° path: start about 23.6 NM out, fly about 743 ft/min, and the descent takes about 10 minutes.
Accuracy and practical tips
Ground speed often changes in the descent, so recheck the required rate as you go. Many light-aircraft pilots prefer 500 ft/min for passenger comfort; enter a smaller angle to see how much earlier that means starting down.
Standard descent-planning geometry. Follow ATC instructions, published procedures and aircraft limitations.
Last reviewed: October 2026
Read the guide: QNH, QFE and QNE: Altimeter Settings Explained
Frequently asked questions
What is the 3-to-1 rule?
You need about 3 nautical miles for every 1,000 ft of altitude to lose on a 3° path.
How do I estimate vertical speed quickly?
Multiply ground speed by 5. At 120 kt that gives 600 ft/min for a 3° path.
Why use ground speed, not airspeed?
The descent path is fixed over the ground, so the rate needed depends on how fast you cover that ground.
Can I plan a 500 ft/min descent?
Yes. Reduce the angle until the rate shows about 500 ft/min and read the new top-of-descent distance.