BLDC Motor Kv to Kt Conversion
Kt = 9.549 / Kv
Quick answer
This calculator solves Kt = 30/π / Kv ≈ 9.549 / Kv for Torque Constant (N·m/A). With Velocity Constant (RPM/V) 1.1, the result is 8.681. It solves in 2 directions, so you can enter the values you have and get the one you need.
Calculator
Formula
Description
The torque constant Kt (N·m/A) and velocity constant Kv (RPM/V) of a brushless DC motor are reciprocally related through the factor 30/π ≈ 9.549. This relationship comes from the fundamental motor equation: back-EMF = Kv × speed, and torque = Kt × current, with power conservation requiring V×I = τ×ω. Kv is commonly used in the RC/drone community (higher Kv = faster, less torque), while Kt is used in industrial servo applications (higher Kt = more torque per amp). They are two ways of expressing the same motor parameter.
Variables
- Kt — Torque constant in N·m per ampere
- Kv — Velocity (back-EMF) constant in RPM per volt
Practical Notes
The 9.549 factor comes from converting between RPM and rad/s: 30/π. In consistent SI units (rad/s per volt for Kv and N·m/A for Kt), Kt = 1/Kv exactly. Example: a 1000 Kv motor has Kt = 9.549/1000 = 0.00955 N·m/A = 9.55 mN·m/A. At 10 A, it produces 95.5 mN·m of torque. Motor efficiency determines how much of the electrical power is converted to mechanical power.
Symbols and units
| Symbol | Meaning | Default unit | Accepted units |
|---|---|---|---|
| Kt | Torque Constant (N·m/A) | — | — |
| Kv | Velocity Constant (RPM/V) | — | — |
Step by step
- 1. What you know: Velocity Constant (RPM/V) 1.1
- 2. The relation: Kt = 30/π / Kv ≈ 9.549 / Kv
- 3. Substitute: Kv = 1.1
- 4. Result: Torque Constant (N·m/A) = 8.681
Worked examples
Minimum range
Given: Velocity Constant (RPM/V) 0.055
Result: Torque Constant (N·m/A) = 173.6
Low range
Given: Velocity Constant (RPM/V) 0.55
Result: Torque Constant (N·m/A) = 17.36
Typical
Given: Velocity Constant (RPM/V) 1.1
Result: Torque Constant (N·m/A) = 8.681
High range
Given: Velocity Constant (RPM/V) 1.76
Result: Torque Constant (N·m/A) = 5.426
Maximum range
Given: Velocity Constant (RPM/V) 17.6
Result: Torque Constant (N·m/A) = 0.5426
Solving for each variable
Solve for Torque Constant (N·m/A)
Velocity Constant (RPM/V) 0.055 → 173.6
Solve for Velocity Constant (RPM/V)
Torque Constant (N·m/A) 0.025 → 382
How Torque Constant (N·m/A) changes with Velocity Constant (RPM/V)
| Velocity Constant (RPM/V) (input) | Torque Constant (N·m/A) (result) |
|---|---|
| 0.242 | 39.46 |
| 0.605 | 15.78 |
| 1.21 | 7.892 |
| 1.815 | 5.261 |
| 2.42 | 3.946 |
| 3.63 | 2.631 |
| 4.84 | 1.973 |
| 9.68 | 0.9865 |
| 16.94 | 0.5637 |
| 24.2 | 0.3946 |
Embed this calculator
Paste this into any page. It keeps working when this page updates, and credits the source.
<iframe src="https://vbatpower.com/embed/bldc-kv-kt/" width="100%" height="460" style="border:1px solid #1f2a37;border-radius:12px" loading="lazy" title="BLDC Motor Kv to Kt Conversion"></iframe>
<p><a href="https://vbatpower.com/formulas/bldc-kv-kt/">BLDC Motor Kv to Kt Conversion</a> Calculator by vbatpower.com</p>Frequently asked questions
How do you calculate BLDC Motor Kv to Kt Conversion?
Use Kt = 30/π / Kv ≈ 9.549 / Kv. With Velocity Constant (RPM/V) 1.1, Torque Constant (N·m/A) works out to 8.681.
What is the formula for BLDC Motor Kv to Kt Conversion?
The formula is Kt = 30/π / Kv ≈ 9.549 / Kv. The torque constant Kt (N·m/A) and velocity constant Kv (RPM/V) of a brushless DC motor are reciprocally related through the factor 30/π ≈ 9.549.
How do you find Velocity Constant (RPM/V) when you know the other values?
Rearrange for Velocity Constant (RPM/V): with Torque Constant (N·m/A) 0.025, Velocity Constant (RPM/V) is 382.
Related Concepts
All Motors & Mechanical formulas →Need more features?
Save calculations, import telemetry data, simulate battery discharge, and collaborate with your team.
Try the App