Thrust-to-Weight Ratio Calculator (Drones & RC Aircraft)
Thrust-to-weight ratio of a multirotor or RC aeroplane from motor thrust, motor count and all-up weight — hover throttle, spare thrust for climbing and wind, maximum payload for a target ratio, vertical acceleration and recommendations by flying style.
How it works
TWR = (thrust per motor × motors × (1 − derating)) ÷ all-up weight; hover throttle ≈ 1 ÷ TWR; vertical acceleration = (TWR − 1) × g; payload at target ratio = total thrust ÷ target − AUW
The thrust-to-weight ratio decides how an aircraft feels. A multirotor must hover, so its motors sit at roughly 1/TWR of full power just to hold altitude: at 2:1 they idle at half throttle with the other half in reserve for climbing, stopping a descent and fighting wind, which is the accepted minimum; camera ships live at 2–3, freestyle quads at 4–5, racers far higher. Aeroplanes are different — the wing carries the weight — so ratios below 1 are normal, 0.5 gives a brisk climb and anything over 1 can hang on the prop. Thrust figures from manufacturers are measured static, on a bench, with a fresh battery; hot thin air and sagging cells cut them, so derate before trusting the margin. Payload capacity is whatever weight can be added before the ratio falls to your chosen floor.
Worked example
Four motors rated 1,150 g each, derated 10%, give 4,140 g of thrust on an 1,800 g quad: 2.3:1 — a good camera platform hovering at about 43% throttle with 2,340 g of spare thrust (12.8 m/s² max climb). It could carry 270 g more before dropping to 2:1.
Frequently asked questions
How do I find thrust per motor?
From the motor maker’s thrust table for your prop and cell count, or measure with a thrust stand; do not scale a different prop’s figure — thrust changes roughly with the square of diameter and the pitch.
Is more always better?
No — very high ratios waste weight on motors and batteries, make the craft twitchy and shorten flight time; match the ratio to the mission.
Related calculators
Hobby estimate from standard formulas; motor, ESC and propeller data vary by manufacturer — verify with a wattmeter and start with conservative settings.