Motor KV Explained

calendar Jul 13, 2026 · 3 min read · fpv motor kv voltage rpm efficiency selection  ·
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KV is the most misunderstood motor specification in FPV. It is not a measure of motor quality or power — it is a ratio that determines how much RPM you get per volt.

Definition

KV = RPM per Volt (unloaded)

A motor rated 2400 KV spinning at 16.8 V (4S fully charged) will spin at:

1RPM = KV × Voltage
2RPM = 2400 × 16.8 ≈ 40,320 RPM (no load)

Under load (with a prop), RPM will be lower — typically 65–85% of no-load RPM depending on prop size and throttle.

What KV Affects

Higher KVLower KV
Higher RPMLower RPM
More suited to small propsMore suited to large props
Less torqueMore torque
Runs hotter under loadRuns cooler under load
Needs lower voltage (2S, 3S)Needs higher voltage (4S, 6S)

The stator windings determine KV: fewer, thicker windings = higher KV; more, thinner windings = lower KV.

Voltage and KV Together

KV is meaningless without knowing the operating voltage. The same RPM can be achieved with different KV × Voltage combinations:

12400 KV × 14.8 V (4S nominal) = 35,520 RPM
21750 KV × 22.2 V (6S nominal) = 38,850 RPM

Both setups deliver similar RPM — but the 6S motor has more torque available to turn a larger prop efficiently.

Practical KV Guide by Frame Size

Frame sizeCommon voltageTypical KV rangeProp size
1" whoop1S (3.7 V)15,000–20,000 KV31 mm
2.5" micro2S–3S5,000–8,000 KV2.5"
3" toothpick3S–4S3,000–5,000 KV3"
5" freestyle4S–6S1,700–2,500 KV5"
7" long range4S–6S1,300–1,800 KV7"
10" cinematic4S–6S700–1,000 KV9"–10"

KV Calculator

Target RPM from KV and voltage:

1RPM = KV × Voltage

KV needed for a target RPM at a known voltage:

1KV = Target RPM ÷ Voltage

Loaded RPM estimate (approximate):

1Loaded RPM ≈ KV × Voltage × 0.75

Example: You want ~25,000 loaded RPM on 4S (14.8 V nominal):

1KV ≈ 25,000 ÷ (14.8 × 0.75) ≈ 25,000 ÷ 11.1 ≈ 2,250 KV

→ A 2300–2450 KV motor on 4S is a reasonable target.

KV and Efficiency

Lower KV motors running at higher voltage are generally more efficient for the same power output. On the same stator, winding resistance scales as R ∝ 1/KV² (more turns of thinner wire), so copper loss in the motor at equal output is about the same; the higher-voltage, lower-current build saves I²R loss in the battery, ESC and wiring.

This is part of why 6S builds on a 5" frame achieve better flight times despite similar physical size — less current means less voltage sag and less energy wasted as heat outside the motor.

Notes

  • KV is a no-load spec. Real-world RPM depends on prop pitch, prop diameter, throttle, and air density.
  • Stator dimensions (e.g., 2306 = 23 mm diameter × 6 mm height) determine torque capacity and heat dissipation, independent of KV.
  • Two motors with the same stator and same KV from different manufacturers can behave very differently — winding quality, magnet strength, and bearing precision all matter.

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