By Renzo, CPL · Updated March 2026

Descent Rate Calculator

Calculate the required descent rate (FPM) for any glideslope angle and ground speed. Plan ILS, RNAV, and visual approaches with precision.

Quick presets
kts
deg
ft
NM
Required Descent Rate
637
feet per minute
Rule of Thumb (3°)
120 × 5 = 600
FPM (approximate for 3°)
Descent Gradient
5.2%
318 ft/NM
3.0°637 FPMGS 120 kts

Descent Rate Reference Table (3° glideslope)

Ground Speed (kts)Descent Rate (FPM)
60318
70372
80425
90478
100531
110584
120637
130690
140743
150796
160849
180955
2001,061

Highlighted row matches your current ground speed. The ft/NM value is constant for a given angle.

Pilot Quick Reference

Rules of Thumb

  • 3°GS × 5 = descent rate in FPM (e.g., 120 kts × 5 = 600 FPM)
  • 3°GS ÷ 2 = nm per 1,000 ft (e.g., 120 kts → lose 1,000 ft every 6 NM... start descent 3 NM per 1,000 ft to lose, at idle)
  • TODTop of Descent: altitude to lose (in thousands) × 3 = NM from field

Common Glideslopes

  • Standard ILS3.0°
  • RNAV (LPV/LNAV+V)3.0° - 3.5°
  • Visual / VASI / PAPI3.0° - 4.0°
  • London City (EGLC)5.5°
  • Lugano (LSZA)6.65°

How Descent Rate Is Calculated

The descent rate (in feet per minute) required to maintain a constant glideslope depends on two variables: your ground speed and the glideslope angle. The precise formula is:

Descent Rate (FPM) = Ground Speed (kts) × tan(Glideslope Angle) × 101.27

The constant 101.27 comes from the unit conversion: 1 knot = 101.27 feet per minute (6,076.12 ft/NM divided by 60 min/hr). For the standard 3-degree ILS glideslope, tan(3°) ≈ 0.05241, so the formula simplifies to:

Descent Rate ≈ Ground Speed × 5.30 FPM

Rounded in practice to GS × 5

Why Ground Speed, Not Airspeed?

The glideslope is a fixed path through space. Your descent rate must match the vertical component of that path relative to the ground. If you have a 20-knot headwind, your ground speed is 20 knots less than your indicated airspeed, so you need less FPM to stay on glideslope. Conversely, a tailwind increases ground speed and requires more FPM.

Descent Gradient vs. Descent Rate

The descent gradient (ft/NM) is constant for a given angle regardless of speed. A 3-degree path always descends at about 318 ft per nautical mile. The descent rate (FPM) varies with ground speed because faster aircraft traverse more nautical miles per minute. Both describe the same geometric path, just in different units.

Tips for Planning Descents

  • Start with ground speed, not airspeed. Check your GPS or FMS ground speed readout, especially in strong wind conditions. The difference can be 30+ knots.
  • Use the 3:1 rule for en-route descents. To lose 1,000 feet, plan to begin 3 NM before the point where you need to be at that altitude. Multiply altitude to lose (in thousands) by 3 for the distance.
  • Add 1 NM per 10 knots of tailwind to your top-of-descent calculation. Tailwinds push you through the descent, so starting earlier prevents high rates close to the airport.
  • Monitor the VDEV or glideslope indicator during the approach. Even a perfect calculation needs real-time adjustments for changing winds.
  • For non-precision approaches, calculate a Visual Descent Point (VDP) so you can plan a stabilized descent from MDA to the runway. Divide height above TDZE by 300 to get the VDP distance in NM.
  • Stabilized approach criteria: Most operators require being stabilized by 1,000 feet AGL (IFR) or 500 feet AGL (VFR), with a descent rate below 1,000 FPM. Plan accordingly.

Frequently Asked Questions

How do you calculate descent rate for a 3 degree glideslope?
The simplest rule of thumb: multiply your ground speed by 5. For example, at 120 knots ground speed, you need approximately 600 FPM descent rate. The precise formula is: Descent Rate = Ground Speed (kts) x tan(glideslope angle) x 101.27. For 3 degrees this gives GS x 5.30, which rounds nicely to GS x 5.
What is the standard ILS glideslope angle?
The standard ILS glideslope is 3.0 degrees. This is the most common angle worldwide and is the basis for the GS x 5 rule of thumb. Some airports have steeper glideslopes due to terrain or noise abatement — for example, London City Airport uses 5.5 degrees.
What descent rate do I need at 90 knots on a 3 degree glideslope?
At 90 knots ground speed on a 3-degree glideslope, you need approximately 478 FPM. Using the rule of thumb (90 x 5 = 450 FPM) gives a close approximation that works well in practice.
How do I calculate top of descent (TOD)?
A common rule of thumb: multiply the altitude to lose (in thousands of feet) by 3. This gives you the distance in nautical miles at which to begin your descent, assuming a 3-degree path. For example, if you need to descend 6,000 feet, begin your descent 18 NM out. For a more precise answer, enter your altitude to lose and distance in the calculator above.
What is the difference between descent rate and descent gradient?
Descent rate is measured in feet per minute (FPM) and depends on your ground speed — faster aircraft need higher FPM to maintain the same path. Descent gradient is measured in feet per nautical mile (ft/NM) or as a percentage, and it describes the geometric path angle independent of speed. A 3-degree glideslope always equals approximately 318 ft/NM regardless of speed.
Why does ground speed matter for descent rate?
Ground speed determines how quickly you cover distance. If your ground speed increases (e.g., due to a tailwind), you cover more distance per minute, so you need a higher descent rate in FPM to maintain the same glideslope angle. This is why pilots increase their target descent rate when they have a tailwind on approach.
How do I adjust descent rate for a non-standard glideslope?
Use the formula: Descent Rate = GS x tan(angle) x 101.27. For a 3.5-degree RNAV approach at 130 knots, that is 130 x tan(3.5) x 101.27 = 804 FPM. Alternatively, select a preset above or enter any custom angle in the calculator.
What descent rate is too high for passengers?
Most airlines limit cabin descent rate to about 300-350 FPM of cabin altitude change for passenger comfort. In terms of aircraft descent rate, anything above 1,500 FPM during approach is considered aggressive, and rates above 1,000 FPM below 1,000 feet AGL are a stabilized approach criterion violation at many airlines.
How does wind affect descent rate on an ILS?
Wind affects your ground speed, which changes the required descent rate. A headwind reduces ground speed, requiring a lower FPM to stay on glideslope. A tailwind increases ground speed, requiring a higher FPM. Always calculate descent rate based on ground speed, not indicated airspeed. Monitor the glideslope indicator and adjust as needed.
What is a Visual Descent Point (VDP)?
A VDP is the point on a non-precision approach from which a normal descent (typically 3 degrees) can be made to the runway threshold. If no VDP is charted, you can calculate it: divide the height above touchdown by 300 to get the distance in NM from the threshold. For example, an MDA 600 feet above TDZE gives a VDP at 2.0 NM.

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