How to calculate glide distance
Best-glide ratio is distance over altitude in the same units — 9:1 means 9 feet forward for every foot of altitude you give up. Still-air range in nautical miles is
distance (NM) = (altitude AGL in feet / 6,076.12) × glide ratio
The corresponding descent angle is arctan(1 / ratio). A 9:1 airplane descends at about 6.3°.
Adding wind
The time to come down does not care about the wind: it is altitude divided by the still-air sink rate, and sink rate is best-glide TAS divided by the ratio. Ground distance is then groundspeed times that time. A headwind shortens the range; a tailwind stretches it. In a uniform wind the reachable area is a circle of still-air radius, slid downwind by wind speed times time — you can go farther with the wind at your back, and the worst case is straight into it.
Worked example
6,000 ft AGL, 9:1, 70 kt best-glide TAS, 10 kt headwind:
- Still-air distance ≈ 8.89 NM (47,000+ ft, about 10.2 statute miles). Time to the ground is a little over 7 minutes.
- Into the 10 kt headwind the range shrinks to about 7.6 NM; downwind it grows to about 10.2 NM.
Frequently asked questions
How do I calculate glide distance from altitude?
Multiply AGL by the glide ratio and convert feet to nautical miles (divide by 6,076). Then correct for wind if you have a best-glide speed.
How does wind affect best-glide range?
Time to descend stays the same; ground distance is groundspeed times that time. The reachable area is the still-air circle shifted downwind.
What is a typical best-glide ratio for a light airplane?
Many trainers are around 8:1 to 9:1. Use the POH figure for the airplane you actually fly.
Can I use this in a real engine-out?
Use it for planning and a first estimate. In the airplane, fly the POH speed, pick a field, and fly the airplane. This page is not a substitute for the book or for judgment.