Climb & Descent Gradient Calculator

What is a Climb or Descent Gradient?

A climb or descent gradient expresses the ratio of altitude gained (or lost) to horizontal distance traveled. It is most commonly stated as feet per nautical mile (ft/NM) or as a percentage. A 200 ft/NM gradient means the aircraft gains 200 feet of altitude for every nautical mile of ground distance covered — equivalent to a 3.3% gradient.

Gradients appear throughout aviation: on SID and STAR charts, obstacle departure procedures (ODPs), instrument approach procedures, and published takeoff minimums. When a departure procedure says "climb gradient 350 ft/NM to 4,000 ft," the pilot must verify their aircraft can meet that gradient at the current weight, density altitude, and configuration. Failure to meet a published climb gradient removes the obstacle clearance guarantee provided by that procedure.

When Pilots Use It

• Departure procedures (SIDs / ODPs): The FAA standard minimum climb gradient is 200 ft/NM (3.3%). When obstacles demand more, a higher gradient is published. You need to confirm your aircraft can achieve it before committing to the procedure.
• ILS and RNAV approaches: Standard ILS glidepaths use a 3° descent angle — approximately 318 ft/NM or 5.2%. Non-standard angles (2.5°, 3.5°, 4°) are found at some airports and require recalculating your target descent rate at the current ground speed.
• Missed approach climb gradients: Published missed approach procedures specify a minimum climb gradient (typically 200 ft/NM) to clear terrain during a go-around.
• Non-precision approaches (LNAV, VOR, NDB): With no vertical guidance, you calculate a target descent rate from the gradient and your ground speed to fly a stabilised final.
• Visual descent planning: Knowing your required descent rate for a given angle and ground speed keeps you on a stable visual approach path.
• TERPS/PANS-OPS obstacle clearance: Understanding the relationship between gradient, rate, and ground speed helps pilots evaluate obstacle clearance surfaces when departing non-standard runways.

How to Calculate

Three formulas cover all climb and descent gradient problems:

Gradient (%) = (Height Change ÷ Horizontal Distance) × 100

Rate of Climb/Descent (ft/min) = Gradient (%) × Ground Speed (kt) × 101.3

The constant 101.3 comes from converting knots to feet per minute: 1 knot = 6,076.12 ft/hr ÷ 60 = 101.27 ft/min.

Feet per NM = Gradient (%) × 60.76

To convert between degrees and percentage for small angles: Gradient (%) = tan(angle°) × 100. For the angles pilots encounter (2°–6°), a useful approximation is degrees × 1.745: a 3° glideslope ≈ 5.24%, a 4° approach ≈ 6.99%.

A quick mental math rule for a standard 3° glideslope: multiply your ground speed by 5. At 90 kt, target 450 ft/min. At 120 kt, target 600 ft/min. At 150 kt, target 750 ft/min.

Step-by-Step Examples

Use the rate of climb and descent calculator above for instant results, or work through it manually:

Example 1 — Departure gradient check (SID)

A SID requires a minimum climb gradient of 350 ft/NM to 5,000 ft. Your expected ground speed after takeoff is 110 kt. What rate of climb do you need?

1. Convert ft/NM to gradient %: 350 ÷ 6,076.12 × 100 = 5.76%
2. Calculate required rate: 5.76% × 110 kt × 101.3 = 641 ft/min

You need at least 641 ft/min climb performance at takeoff weight and density altitude to meet the procedure. Check your aircraft POH climb charts for the actual rate under current conditions.

Example 2 — Standard 3° ILS descent rate

You are established on an ILS glideslope at 130 kt ground speed. What descent rate should you target?

1. Convert 3° to gradient %: tan(3°) × 100 = 5.24%
2. Calculate descent rate: 5.24% × 130 kt × 101.3 = 690 ft/min

Quick check: 130 × 5 = 650 ft/min (rule of thumb). The precise answer is 690 ft/min — both are workable references.

Example 3 — Non-precision approach, calculate VDP

A LNAV approach has a descent gradient of 400 ft/NM from FAF to MDA. Your ground speed is 90 kt. What is your target descent rate?

1. Convert ft/NM to gradient %: 400 ÷ 60.76 = 6.58%
2. Calculate descent rate: 6.58% × 90 kt × 101.3 = 599 ft/min

Flying 600 ft/min at 90 kt maintains the required 400 ft/NM gradient to MDA.

Frequently Asked Questions

What is the standard ILS glideslope descent rate?

The standard ILS glideslope is 3°, which corresponds to roughly a 5.2% gradient or about 318 ft/NM. At typical approach speeds, this works out to approximately 5 × ground speed in knots. At 90 kt, target 450 ft/min; at 120 kt, 600 ft/min; at 150 kt, 750 ft/min. The precise calculation is: gradient (%) × ground speed (kt) × 101.3 = ft/min.

What is the standard departure climb gradient and what happens if I can't meet it?

The FAA standard minimum climb gradient is 200 ft/NM (3.3%). If a departure procedure publishes no gradient, 200 ft/NM is assumed. When a higher gradient is published and your aircraft cannot meet it, you must use an alternative departure procedure or apply published climb-in-visual-conditions (CVFP) or non-standard takeoff minimums. Attempting a departure when you cannot meet the published gradient removes TERPS obstacle clearance protection.

Should I use ground speed or indicated airspeed for descent rate calculations?

Always use ground speed. Climb and descent gradients are measured relative to the ground, so wind directly affects the required ft/min rate. A 20 kt headwind on approach reduces your ground speed and therefore lowers the ft/min rate needed to maintain the same glidepath gradient. A tailwind increases ground speed and requires a higher ft/min rate for the same gradient. When ATIS is not available or winds are calm, IAS and ground speed are approximately equal at low altitudes.

How do I convert between degrees and ft/NM?

Convert degrees to a percentage gradient using the tangent function: gradient (%) = tan(angle°) × 100. Then multiply by 60.76 to get ft/NM: ft/NM = tan(angle°) × 6,076.12. For the 3° standard glideslope: tan(3°) × 6,076 ≈ 318 ft/NM. For a 4° approach: tan(4°) × 6,076 ≈ 425 ft/NM. For small angles up to about 6°, the approximation degrees × 105 gives a reasonable ft/NM estimate.

What is a 200 ft/NM climb gradient in ft/min at typical climb speeds?

200 ft/NM equals a 3.29% gradient (200 ÷ 60.76). At 80 kt ground speed: 3.29% × 80 × 101.3 ≈ 267 ft/min. At 100 kt: ≈ 333 ft/min. At 120 kt: ≈ 400 ft/min. Most single-engine piston aircraft exceed 200 ft/NM easily in normal conditions, but density altitude, high weight, or engine issues can reduce climb performance below this minimum — always check performance charts before departing on an instrument procedure.

How do missed approach climb gradients work?

Missed approach procedures are designed to provide obstacle clearance at a standard 200 ft/NM (2.5% for PANS-OPS procedures) climb gradient. If a higher gradient is required, it is published on the approach chart. The climb gradient applies from the missed approach point (MAP) or runway threshold, whichever is later, until reaching the missed approach holding altitude. If you cannot meet a published missed approach gradient, you must fly the approach in VMC or plan an alternate missed approach that keeps you clear of obstacles.