Thermal Lift & Climb Rate Estimator
Enter the altitude you gained circling a thermal and how long it took to get your average climb rate, a general strength read, and — optionally — a projected time to a further target altitude.
Thermal climb rate
How this calculator works
Climb rate here is altitude gained divided by elapsed time, the mirror image of a sink-rate reading. The tool reports it in both m/s and ft/min, and offers a rough, general strength label — weak, moderate, strong, or very strong — based on commonly cited recreational bands rather than a fixed meteorological standard.
If you add a target altitude gain, the tool divides that figure by your measured (unrounded) climb rate to project how long it would take at the same average pace. Real thermals rarely hold a constant rate all the way up, so treat this as a planning estimate to check against the vario as you climb, not a guarantee.
Frequently Asked Questions
How is climb rate calculated?
The same way sink rate is, just in the opposite direction: altitude gained divided by the time it took, giving a rate in metres per second (and converted here to feet per minute too). It's an average over the interval you enter, not an instantaneous reading.
Why does thermal strength vary so much through a flight?
Thermals are rarely uniform columns — they can be stronger near the core and weaker at the edges, change with height as they mix with the surrounding air, and strengthen or weaken through the day as the ground heats and cools. An average climb rate over one circle can look quite different from the next.
What does the projected 'time to target' actually assume?
It assumes your average climb rate stays exactly the same for the rest of the climb, which real thermals rarely do — they tend to weaken with altitude as they approach cloudbase or an inversion. Treat the projection as a rough planning figure, not a promise, and keep watching the vario rather than a fixed number.
Is a stronger thermal always better to core?
Not necessarily — very strong, narrow, or broken-up thermals can also be more turbulent and harder to centre efficiently, especially for a less experienced pilot. Climb rate alone doesn't capture how comfortable or efficient a particular thermal is to work.
General guidance only, not a substitute for certified instruction on thermalling technique. Reading and centring thermals safely — and recognising when one is too strong, broken-up, or close to cloud to keep working — takes supervised practice with a certified instructor, not just a calculator.