Drone Thrust-to-Weight & Hover Throttle
Compute thrust-to-weight ratio and hover throttle for any multirotor using the correct square-law throttle ↔ thrust relationship — not the linear approximation most calculators get wrong. Recommends a motor thrust to hit a target TWR.
Pick the right motor before you buy four of them. Enter your all-up weight, motor count and the manufacturer's max-thrust figure, then set the thrust-to-weight target for the style of flying you want — cinematic, freestyle or race — and the calculator returns TWR, hover throttle (using the correct square-law approximation), and the per-motor thrust you actually need to hit your target. Get this wrong and the craft either won't punch out or wastes a kilogram of battery hauling overkill motors.
curl -X POST https://toolsamurai.com/api/v1/drones-uav/drone-thrust-to-weight \ -H "Authorization: Bearer sk_live_•••••••••••••••" \ -H "Content-Type: application/json" \ -d '{ "auw_grams": 680, "num_motors": "4", "motor_max_thrust_g": 800, "target_twr": 4 }'
The method behind the numbers
Thrust-to-weight ratio is the easy part: TWR = (motors × max thrust per motor) / AUW. The non-obvious part is hover throttle. Most calculators report hover throttle as 1/TWR × 100 — a linear approximation that's wrong because static-thrust scales roughly with the square of throttle (T ∝ throttle², because thrust ∝ RPM² and RPM scales near-linearly with throttle PWM on a BLDC ESC). The correct estimate is hover throttle ≈ √(AUW / total_max_thrust) × 100. The difference matters: a 4:1 TWR quad doesn't hover at 25% throttle — it hovers near 50%. Hover at 25% only happens at 16:1 TWR.
The recommended motor thrust output reverses the math from your target TWR: required per-motor thrust = AUW × TWR_target / motors. Compare that against manufacturer thrust tables to pick a motor + prop combo that actually delivers it on your pack voltage. The verdict tag bands the result so you know whether the build is underpowered, balanced for cinematic, or genuinely race-ready.
See it in practice
Four 2207 motors quoted at 1850 g max thrust each on 5" prop at 4S — target a freestyle 4:1 TWR.
- auw_grams
- 680
- num_motors
- 4
- motor_max_thrust_g
- 1850
- target_twr
- 4
X8 coaxial hauling a Komodo on 6S, motors quoted 2400 g each — target 2.5:1 for stability.
- auw_grams
- 2400
- num_motors
- 8
- motor_max_thrust_g
- 2400
- target_twr
- 2.5
Frequently asked questions
Why isn't hover throttle just 1/TWR?
Because throttle commands RPM (roughly linearly), and thrust scales with RPM squared. Doubling throttle quadruples thrust. So a 4:1 TWR doesn't mean 25% hover throttle — it means about 50% (the square root of 0.25 is 0.5). This calculator shows both numbers so you can see how badly the linear approximation lies.
What TWR should I aim for?
2:1 is the absolute minimum for a craft that can recover from descents and gusts (cinematic, GPS hover). 3:1 feels lively. 4–5:1 is the freestyle sweet spot — punchy without burning packs. 7:1+ is racing territory. Above 10:1 you're carrying motor weight that no longer adds usable performance.
Where do I find max thrust per motor?
Every reputable motor maker — T-Motor, EMAX, BrotherHobby, iFlight, Sunnysky — publishes thrust tables for each motor across props and battery voltages. Use the row for your exact prop and pack S-count. Don't trust the headline 'max thrust' number, which is usually with the largest prop the bell tolerates.
Does this work for hexacopters and octocopters?
Yes. The math is the same — total thrust is motors × per-motor thrust regardless of count. The 'number of motors' input handles tri, quad, hex and octo. For X8 coaxial setups, count both top and bottom motors but expect ~15% lower thrust per motor due to coaxial losses.
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