What Does KV Mean on a Brushless Motor? KV, Torque and Choosing a Drone Motor

KV in one sentence

KV is the speed in rpm that a brushless motor reaches per volt of supply with no load. A 900 KV motor on a 4S battery (14.8 V nominal) spins at about 900 × 14.8 ≈ 13,300 rpm unloaded; with a propeller it typically runs at 75–85 % of that.

KV is the inverse of the torque constant

In SI units the torque constant is Kt (N·m/A) = 60 / (2π × KV) ≈ 9.55 / KV. A 900 KV motor makes about 0.0106 N·m per amp; a 300 KV motor about 0.032 N·m per amp. Low KV does not mean a stronger motor — it means more torque per amp and less speed per volt. Maximum torque is set by how much current the motor can carry without overheating, which depends on stator size and cooling.

How to choose

• Start from the propeller: larger props need lower KV (and usually higher voltage); small FPV props use high KV.
• Fix the battery voltage, then choose KV so that KV × voltage × 0.8 gives the rpm the prop needs for your thrust.
• Check the maker's thrust table at your prop and voltage: current at full throttle must stay below the motor's and ESC's continuous rating.
• Stator size (e.g. 2207 = 22 mm diameter, 7 mm height) sets the power and heat capacity; a bigger stator carries more current.
• For a 2:1 hover margin, the total maximum thrust should be about twice the take-off weight.

KV outside drones

Industrial BLDC datasheets usually give the back-EMF constant Ke in V/krpm instead. Convert with KV = 1000 / Ke(V/krpm). Our spec finder and model pages show the torque constant for every motor, so you can compare drone and industrial motors on the same basis.