Descent Rate Calculator (Aviation)
Calculate required Vertical Speed (VSI) for a 3-degree glide slope or custom gradient. Essential for pilots performing VNAV operations and Top of Descent (TOD) planning.
About
Precise vertical navigation (VNAV) is critical for stabilized approaches and fuel-efficient descents. This tool calculates the required rate of descent (vertical speed) based on ground speed and the desired glide path angle (typically 3°). It also computes the Top of Descent (TOD) point, determining how far out to begin descending to reach a target altitude.
aviation
pilot tools
VNAV
descent planning
glide slope
Formulas
1. Rule of Thumb (3° Glideslope):
VS ≈ GroundSpeed × 5
2. Precise Calculation:
VS = tanθ × GroundSpeed(fpm)
To convert Knots to Feet per Minute for calculation: 1 kt ≈ 101.269 fpm.
3. Top of Descent (TOD) Distance:
Distance = Altcurrent − Alttarget1000 × 3
Reference Data
| Ground Speed (kts) | Vertical Speed (3° Slope) | Descent Gradient (ft/nm) |
|---|---|---|
| 60 kts | 318 fpm | 318 ft |
| 90 kts | 478 fpm | 318 ft |
| 120 kts | 637 fpm | 318 ft |
| 150 kts | 796 fpm | 318 ft |
| 200 kts | 1061 fpm | 318 ft |
| 250 kts | 1327 fpm | 318 ft |
| 450 kts (Cruise) | 2388 fpm | 318 ft |
Frequently Asked Questions
The 3:1 rule states that for every 1,000 feet of altitude you need to lose, you require 3 nautical miles of distance. For example, to lose 10,000 feet, start your descent 30nm out.
Descent geometry is relative to the ground. Wind significantly affects the ground distance covered. A tailwind increases ground speed, requiring a higher rate of descent to maintain the same glide path angle.
Yes. A standard ILS glideslope is 3 degrees. This tool helps pilots monitor whether their vertical speed is appropriate for the glideslope based on their current ground speed.