Climb gradient,
top of descent, solved.
Free climb gradient calculator, top of descent calculator, and descent rate calculator for pilots, dispatchers, and flight planning professionals. Convert between gradient units, calculate required obstacle clearance gradients, and plan precise descent profiles instantly.
Gradient Conversions
Descent Rate Reference Table 3° Glidepath
| Groundspeed (kt) | Descent Rate (ft/min) | ft/NM | Rule of Thumb (GS×5) |
|---|---|---|---|
| 60 | 318 | 318 | 300 |
| 80 | 425 | 318 | 400 |
| 100 | 531 | 318 | 500 |
| 120 | 637 | 318 | 600 |
| 140 | 743 | 318 | 700 |
| 160 | 849 | 318 | 800 |
| 180 | 955 | 318 | 900 |
| 200 | 1061 | 318 | 1000 |
| 250 | 1327 | 318 | 1250 |
| 300 | 1592 | 318 | 1500 |
| 400 | 2123 | 318 | 2000 |
| 500 | 2654 | 318 | 2500 |
Note: The "GS × 5" rule of thumb provides a quick mental approximation for a standard 3° descent. The exact formula yields approximately GS × 5.3, so the rule of thumb slightly underestimates the required descent rate. At higher groundspeeds the difference increases at 500 kt the rule gives 2,500 ft/min versus the exact 2,653 ft/min.
Climb Gradient Converter
Convert between gradient percentage, feet per nautical mile, and degrees. Calculate climb rate in feet per minute at any groundspeed for SID compliance and obstacle clearance.
Required Climb Gradient
Calculate the minimum climb gradient needed to clear obstacles on departure. Enter obstacle height, distance, and airport elevation to find the required ft/NM, percentage, and climb rate.
Top of Descent Calculator
Determine the exact distance to begin descent for any altitude loss and descent angle. Calculate TOD point, required descent rate, and descent time at your planned groundspeed.
Descent Rate Calculator
Calculate the required descent rate in feet per minute for any groundspeed and descent angle. Essential for maintaining a stabilised approach on the 3-degree glidepath or any non-standard descent profile.
How to Use the Climb & Descent Calculator
Climb Gradient Converter
Enter a climb gradient in any unit percentage, feet per nautical mile, or degrees and the calculator converts to all other units instantly. Add your groundspeed to calculate the required climb rate in feet per minute. Use this when a SID procedure publishes a minimum climb gradient and you need to know what rate of climb your aircraft must achieve at its expected climb-out groundspeed.
Required Gradient for Obstacle Clearance
Enter the obstacle height (MSL), distance from the departure runway, airport elevation, and clearance margin. The calculator determines the minimum climb gradient needed to clear the obstacle in ft/NM, percentage, and degrees. The default 35-ft clearance margin follows FAA TERPS Category A/B standards. Add groundspeed to see the minimum climb rate in ft/min your aircraft must maintain.
Top of Descent Calculator
Enter your current cruise altitude, target altitude (e.g. initial approach fix altitude or pattern altitude), and desired descent angle. The calculator gives you the exact distance from the target at which to begin descent. The standard 3° descent angle is pre-set. Add groundspeed to calculate the required descent rate and total descent time. Compare the exact result with the ÷3 rule of thumb.
Descent Rate Calculator
Enter your groundspeed and descent angle to instantly calculate the required descent rate in feet per minute. Pre-set for a standard 3° ILS glideslope. Optionally enter the total altitude to lose for distance and time calculations. Use this during approach briefings to set up the correct vertical speed for a stabilised approach on any standard or non-standard glidepath angle.
Understanding Climb Gradient and Descent Planning
Climb Gradient Fundamentals
- Climb gradient: the ratio of height gained to horizontal distance travelled, expressed as a percentage, ft/NM, or degrees
- Standard ICAO departure obstacle clearance gradient: 3.3% or 200 ft/NM the minimum assumed gradient if no higher gradient is published
- SID minimum climb gradients: published on departure charts when obstacle clearance requires more than the standard 3.3%
- Gradient vs. climb rate: gradient is independent of speed (ft/NM), while climb rate (ft/min) depends on groundspeed
- Wind effect: headwind increases gradient (same ft/min over less ground), tailwind decreases it always use groundspeed, not airspeed
Top of Descent Planning
- Standard descent angle: 3° is the standard ILS glideslope angle, also used as the default for VNAV descent planning
- Rule of thumb (3° descent): divide altitude to lose by 300 e.g. 30,000 ft ÷ 300 = 100 NM from destination
- Rule of thumb (descent rate): multiply groundspeed by 5 e.g. 250 kt × 5 = 1,250 ft/min for a 3° descent
- Steep approaches: some airports (e.g. London City, Lugano) require approach angles of 5.5° or more these significantly increase required descent rate
- Speed restrictions: ATC altitude/speed restrictions (e.g. 250 kt below FL100) require recalculating descent rate at each speed change
Stabilised Approach Criteria
- 1000 ft AGL (IMC) or 500 ft AGL (VMC): aircraft must be in landing configuration, on speed, on glidepath, with appropriate descent rate
- Maximum descent rate on approach: typically 1,000 ft/min exceeding this indicates an unstabilised approach requiring a go-around
- Glidepath deviation: half-dot deviation on ILS or PAPI indication of 'too high' or 'too low' requires corrective action
- Non-precision approaches: constant-descent final approach (CDFA) technique uses the same 3° descent calculation as a precision approach
- Visual approaches: calculating descent rate before the approach ensures a stabilised profile even without electronic glidepath guidance
Key Relationship: Gradient (%), ft/NM, degrees, and ft/min are all expressions of the same flight path angle. The critical distinction is that gradient (%) and ft/NM are ground-referenced and independent of speed, while ft/min depends on groundspeed. A SID requiring 300 ft/NM means a faster aircraft needs a higher ft/min climb rate than a slower one to achieve the same gradient. Always convert published gradients to ft/min using your expected climb-out groundspeed.
Why Use a Climb Gradient & Descent Calculator?
SID Compliance Verification
SID charts publish minimum climb gradients in ft/NM or percentage. Converting to the climb rate your aircraft must achieve at its actual groundspeed is essential for verifying compliance before departure.
Obstacle Clearance Analysis
Determine whether your aircraft's climb performance is sufficient to clear obstacles on the departure path, accounting for airport elevation, obstacle height, distance, and required clearance margins.
Precise Descent Planning
Calculate the exact top-of-descent point for any altitude change and descent angle. Plan fuel-efficient idle descents instead of step-downs that increase fuel burn and ATC workload.
Stabilised Approach Setup
Know the exact descent rate needed for a stabilised approach at your approach groundspeed. Critical for non-precision approaches, visual approaches, and non-standard glidepath angles.
VNAV Cross-Check
Cross-check your FMS VNAV calculations with independent manual computation. A valuable backup when the FMS path seems incorrect or during VNAV troubleshooting.
Free and Instant
No registration, no subscription. All four calculators available instantly in your browser on the ramp, in the briefing room, or at the dispatch desk.
Frequently Asked Questions About Climb Gradient and Descent Calculations
How do I convert a climb gradient from percentage to feet per nautical mile?
Multiply the gradient percentage by 60.76 (which is 6,076.115 ft per NM ÷ 100). For example, a 3.3% gradient equals 3.3 × 60.76 = approximately 200 ft/NM. This is the standard ICAO departure obstacle clearance gradient. Conversely, divide ft/NM by 60.76 to get the percentage.
How do I calculate the climb rate needed for a published SID gradient?
Multiply the gradient in ft/NM by your groundspeed in knots, then divide by 60. For example, a 300 ft/NM gradient at 150 kt groundspeed requires 300 × 150 ÷ 60 = 750 ft/min. Use groundspeed (not airspeed) because the gradient is measured over the ground. A headwind helps it gives you more altitude gain per NM of ground covered.
What is the standard departure climb gradient?
The standard ICAO obstacle clearance gradient for departures is 3.3% or 200 ft/NM. This gradient is assumed in the design of all departure procedures unless a higher gradient is specifically published. If your aircraft cannot achieve 200 ft/NM at its climb-out groundspeed, obstacle clearance on a standard departure is not guaranteed. SID procedures may publish higher gradients some mountain airports require 500+ ft/NM.
How do I calculate top of descent for a 3-degree descent?
The exact formula is: TOD distance (NM) = altitude to lose ÷ (tan(3°) × 6,076.115). The quick rule of thumb is: divide altitude to lose by 300. For example, descending from FL360 to 3,000 ft: (36,000 − 3,000) ÷ 300 = 110 NM. The exact calculation gives 103.7 NM the rule of thumb adds a slight buffer, which is operationally useful.
What descent rate do I need for a 3-degree glideslope?
The quick rule of thumb is groundspeed × 5. At 140 kt approach speed, that's approximately 700 ft/min. The exact formula (tan(3°) × 6,076 × GS/60) gives approximately GS × 5.3, so the rule of thumb slightly underestimates. At 140 kt the exact rate is 742 ft/min. For ILS approaches, set the calculated rate and fine-tune to stay on the glideslope.
Why does wind affect climb gradient but not descent angle?
Both climb gradient and descent angle are affected by wind because they're measured over the ground. A headwind reduces your groundspeed, meaning you cover less ground per minute while still climbing or descending at the same ft/min this increases your gradient over the ground. A tailwind does the opposite. This is why it's essential to use groundspeed (not TAS or IAS) when calculating ft/min from a published gradient. On approach, a strong tailwind means you need a higher descent rate to maintain the same 3° path over the ground.
What is the difference between a climb gradient and a climb rate?
Climb gradient (expressed as %, ft/NM, or degrees) describes the steepness of the flight path relative to the ground it's speed-independent. Climb rate (ft/min) describes how fast you gain altitude it depends on both the gradient and your groundspeed. Two aircraft on the same gradient will have different ft/min if they're at different speeds. Published SID gradients are in ft/NM or % because they must be met regardless of aircraft speed.
How do I calculate descent rate for a non-standard approach angle?
Use the same formula with the non-standard angle: descent rate = tan(angle) × 6,076.115 × (GS ÷ 60). For example, London City Airport requires a 5.5° approach. At 140 kt: tan(5.5°) × 6,076.115 × (140 ÷ 60) = 1,365 ft/min. This is nearly double the standard 3° rate of 742 ft/min at the same speed, which is why steep approaches require special crew training and aircraft certification.
Can I use this calculator for VNAV descent planning?
Yes. The Top of Descent calculator replicates the basic VNAV TOD computation: given your cruise altitude, target altitude, and desired descent angle, it calculates the distance at which to begin descent. This is the same calculation your FMS performs for the VNAV descent path. You can use this calculator to cross-check FMS VNAV, plan descents when VNAV is unavailable, or verify that an ATC-assigned altitude can be reached by a specific waypoint.