Glide Ratio Calculator
Enter either a distance-and-height reading or an airspeed-and-sink-rate pair to get your glide ratio, with an optional wind adjustment to see the ground-relative version.
Glide ratio
How this calculator works
Glide ratio is a single division: distance travelled over height lost. When you give a distance and height directly, that's exactly what's computed. When you give an airspeed and sink rate instead, the tool converts your airspeed from km/h to m/s and divides it by your sink rate in m/s — the same ratio, derived from your glider's polar rather than a completed flight.
Add a wind speed (positive for a tailwind, negative for a headwind) and the tool also works out your ground speed and a ground-adjusted glide ratio, which is the number that actually matters for judging whether you'll reach a landing field or ridge against or with the wind.
Frequently Asked Questions
What is glide ratio, exactly?
Glide ratio (also called L/D, for lift over drag) is how far a glider travels forward for every unit of height it loses. A ratio of 9:1 means 9 metres of forward travel for every 1 metre of altitude given up. It's the number that tells you how far you can reach from a given height, in still air.
Why does this tool ask for either distance-and-height OR airspeed-and-sink-rate?
They are two ways to measure the same thing. If you already know how far you travelled and how much height that cost (from a flight log or GPS track), the ratio is direct division. If instead you know your glider's airspeed and its sink rate at that speed (from a polar chart or a vario reading), the same ratio falls out of dividing one by the other, after converting km/h to m/s.
How does wind change the result?
Wind does not change your still-air glide ratio — that number depends only on your glider and airspeed. What it changes is how far you get over the GROUND: a headwind eats into your ground distance for the same height lost (a worse ground glide), while a tailwind stretches it (a better ground glide). This tool reports both the still-air ratio and, if you give it a wind speed, the ground-adjusted one.
Can my ground glide ratio go negative?
If a headwind is stronger than your airspeed, your ground speed becomes negative — you are being blown backwards relative to the ground even though you're still flying forward through the air. The calculator will show a negative ground speed and ratio in that case, which is a real and important situation to recognise before committing to a glide into wind.
General guidance only, not a substitute for certified instruction on final-glide planning. Real glide performance is affected by wing loading, trim setting, turbulence, and pilot input — always keep a conservative safety margin over any number this tool gives you, especially on a glide over unlandable terrain.