Aviation Rate of Descent Calculator
Use this tool to calculate the required Rate of Descent (ROD) in feet per minute to reach a specific target altitude over a set distance. This is essential for IFR approaches, VFR descent planning, and maintaining a stabilized approach.
Descent Profile Results
How to Calculate Rate of Descent in Aviation
Calculating the correct Rate of Descent (ROD) is a fundamental skill for pilots, ensuring smooth transitions from cruise altitude to approach fixes or traffic pattern altitude. Whether you are flying an ILS approach or a VFR arrival, managing your vertical energy is critical for passenger comfort and aircraft safety.
The Logic Behind the Calculation
To determine your required vertical speed, you must know how much altitude you need to lose and how long you have to lose it. The time available is determined by your Ground Speed and the Distance to your target.
Time (min) = (Distance (NM) / Ground Speed (kts)) × 60
ROD (fpm) = Altitude to Lose (ft) / Time (min)
The 3-Degree Glide Slope Rule of Thumb
For a standard stabilized approach, pilots typically aim for a 3-degree glide path. This provides a safe and comfortable descent angle. There is a very popular mental math shortcut for this:
Example: At 120 knots, 120 × 5 = 600 ft/min.
Alternatively, you can halve your ground speed and add a zero (e.g., 120 / 2 = 60, add 0 = 600).
Descent Gradient
The descent gradient tells you how many feet you drop for every nautical mile traveled forward. A standard 3-degree slope is approximately 318 feet per nautical mile (often rounded to 300 or 320 for mental math).
- Gradient Formula: Altitude to Lose / Distance (NM)
- If your gradient is significantly higher than 320 ft/NM, you may need drag devices (flaps, gear, speed brakes) to descend without gaining excessive airspeed.
Practical Example
Imagine you are flying at 10,000 feet and need to cross a fix at 2,000 feet. The fix is 20 NM away, and your ground speed is 150 knots.
- Altitude to Lose: 10,000 – 2,000 = 8,000 ft.
- Time to Fix: (20 / 150) * 60 = 8 minutes.
- Required ROD: 8,000 ft / 8 min = 1,000 ft/min.
Using the calculator above allows you to verify your mental math and ensure you meet altitude restrictions precisely.