Aircraft Glide Distance Formula & Glide Ratio
Still-air glide distance is height available multiplied by glide ratio. Keep the distance units consistent, then account separately for wind, terrain, turns and aircraft configuration.
Glide distance formula
Horizontal glide distance = height available × glide ratio. If height is entered in feet, the first result is also in feet. To convert feet to nautical miles, divide by approximately 6,076.12.
Example: 5,000 feet of usable height with a 9:1 glide ratio gives 45,000 feet of theoretical horizontal distance. Dividing by 6,076.12 gives about 7.4 NM. Dividing by 5,280 gives about 8.5 statute miles.
What a 9:1 glide ratio means
A 9:1 glide ratio means about nine units forward for every one unit down under the conditions represented by that ratio. The units can be feet, meters or another consistent distance unit. The ratio is a geometric way to describe lift-to-drag performance; it is not an airspeed.
Use height above the landing surface
The formula needs height available to lose, not simply altitude above sea level. If the aircraft is at 7,000 feet MSL and the landing surface is at 2,000 feet MSL, a simple example starts with about 5,000 feet of height. Terrain and obstacles between the aircraft and the landing site can reduce the practical margin.
Best glide speed is a different quantity
Best glide speed is an aircraft-specific airspeed associated with a favorable lift-to-drag condition. Glide ratio is the distance relationship produced by that aerodynamic condition. They should not be treated as interchangeable values. See best glide speed versus glide ratio for a deeper explanation.
Wind changes ground distance
The formula above is a still-air geometric estimate. A headwind reduces the distance traveled over the ground during the descent, while a tailwind increases it. Crosswind changes the ground track and may make a direct path to a landing area impractical. The calculator therefore should not be treated as a precise reachable-radius tool.
Turns and configuration reduce margin
Bank angle, maneuvering, landing gear, flaps, a windmilling propeller, ice, damage and other sources of drag can reduce real glide performance. An emergency landing also requires enough energy and position to arrive at the landing area in a usable direction. Read emergency glide planning concepts for the judgment side of the problem.
How far can an airplane glide from 5,000 feet?
There is no single answer because aircraft have different glide performance. With a 9:1 training example and 5,000 feet of usable height, the no-wind geometric result is about 7.4 NM. An aircraft with a different approved glide ratio, different configuration, different wind or different terrain situation will produce a different practical answer.
Finding the ratio in the aircraft manual
A model name alone does not supply a glide ratio. For a Cessna 172 or any other airplane, identify the exact model, applicable POH/AFM, supplements, weight, configuration and propeller conditions before reading a glide chart. If a chart shows distance versus height, use two points from the same published curve: a hypothetical 8 NM at 5,000 ft gives 8 × 6,076.12 ÷ 5,000 ≈ 9.72:1. That is invented arithmetic, not Cessna performance data.
Do not turn a chart’s stated conditions into a universal ratio or treat a still-air result as a reachable landing radius. Use the chart and emergency procedure as published. The FAA Airplane Flying Handbook explains glide and emergency-landing concepts; the aircraft manual supplies the speeds and performance.
Use the calculator as a cross-check
The PilotDesk aircraft glide distance calculator takes height available and glide ratio, then returns nautical miles, horizontal feet and statute miles. It is useful for study, classroom examples and checking arithmetic. For an actual aircraft, the current POH or AFM controls the speeds, procedures and performance information.
Continue studying
Best glide speed vs glide ratio · Emergency glide planning · Pilot checkride math · Aircraft performance reference