How to Calculate Rate of Climb of Aircraft

Aircraft Rate of Climb Calculator

Calculate required Vertical Speed based on Ground Speed and Gradient

IFR / Departure Climb

Time to Climb

Your speed relative to the ground (GS).

Standard SID gradient is often 200 ft/NM.

Check your POH for performance data at this weight/temp.

The Rate of Climb (ROC) is one of the most critical performance metrics for any aircraft. It represents the vertical speed at which an aircraft increases its altitude, typically measured in feet per minute (fpm). Understanding how to calculate ROC is essential for flight planning, ensuring obstacle clearance during departure (Instrument Departure Procedures), and managing fuel efficiency.

1. The Formula for IFR Departures

Pilots often need to convert a required climb gradient (given in feet per Nautical Mile on departure charts) into a vertical speed indicated on the cockpit instruments. The standard Instrument Flight Rules (IFR) formula is:

ROC (fpm) = (Ground Speed × Climb Gradient) / 60

Where:

• Ground Speed (Knots): The speed of the aircraft relative to the ground. As ground speed increases, the rate of climb must increase to maintain the same angle of ascent relative to the terrain.
• Climb Gradient (ft/NM): The altitude gained per nautical mile of horizontal distance flown. A standard SID (Standard Instrument Departure) often requires 200 ft/NM.

Realistic Example:

Imagine you are flying a Cessna 182. You are departing an airport with a required climb gradient of 300 ft/NM due to nearby mountains. Your ground speed during the climb is 100 knots.

Using the calculator above:

• Calculation: (100 × 300) / 60
• Result: 500 fpm

You must maintain at least 500 feet per minute on your Vertical Speed Indicator (VSI) to clear the obstacles.

2. Calculating Time to Climb

For fuel planning and en-route navigation, pilots need to calculate how long it will take to reach a cruising altitude. This is a simpler function of distance (vertical) and speed (vertical).

Time (min) = (Target Altitude – Starting Altitude) / Average ROC

Note that "Average ROC" is crucial here. Naturally aspirated engines lose power as altitude increases, meaning your climb rate at sea level might be 1000 fpm, but at 10,000 feet it might drop to 200 fpm. Pilots usually take an average value from the Pilot Operating Handbook (POH).

3. Factors Affecting Rate of Climb

Several physical factors influence the actual ROC an aircraft can achieve:

• Excess Power: Physically, ROC depends on the difference between power available (engine output) and power required (drag). ROC = Excess Power / Weight.
• Weight: Heavier aircraft require more power to sustain lift, leaving less excess power for climbing. A fully loaded plane will climb significantly slower than a light one.
• Density Altitude: High temperatures and high airport elevations reduce air density. This reduces engine performance and wing lift, drastically lowering the Rate of Climb.
• Flap Configuration: extending flaps increases drag (Power Required), which reduces Excess Power and consequently lowers the climb rate.

Vy vs. Vx Speeds

When calculating climb performance, pilots choose between two specific airspeeds:

• Vx (Best Angle of Climb): The speed that provides the greatest altitude gain over a given horizontal distance. Use this for clearing obstacles (like trees at the end of a runway).
• Vy (Best Rate of Climb): The speed that provides the greatest altitude gain over time. Use this for getting to cruise altitude quickly.

Use the calculator above to verify that your aircraft's performance (at Vy or Vx) meets the required gradients for your specific departure procedure.