Compute torque from current, power, voltage, and RPM. Review efficiency, losses, and constants quickly today. Make better motor sizing decisions across demanding engineering projects.
| Parameter | Example Value |
|---|---|
| Calculation mode | Auto |
| Line voltage | 48 V |
| Line current | 35 A |
| No-load current | 2 A |
| Efficiency | 88% |
| Speed | 3000 RPM |
| Kt constant | 0.08 Nm/A |
| Kv constant | 120 RPM/V |
| Phase resistance | 0.09 Ohm |
| Pole pairs | 7 |
| Gear ratio | 3.2 |
| Gear efficiency | 92% |
| Selected shaft torque | 2.6400 Nm |
| Gearbox output torque | 7.7722 Nm |
1. Input power: Pin = V × I
2. Angular speed: ω = 2π × RPM ÷ 60
3. Torque from current: Tcurrent = Kt × (I − I0)
4. Estimated output power: Pout = Pin × η
5. Torque from power: Tpower = Pout ÷ ω
6. Copper loss estimate: Pcu = I² × R
7. Back EMF estimate: E = RPM ÷ Kv
8. Electrical frequency: f = Pole Pairs × RPM ÷ 60
9. Gearbox output torque: Tout = Tshaft × Gear Ratio × Gear Efficiency
The auto mode selects the more conservative torque value when both torque methods are available.
Brushless motors power robots, drones, e-bikes, pumps, and CNC systems. Torque decides whether the motor can move the load. Engineers must compare electrical input, speed, losses, and gearing. A simple RPM value never tells the whole story. Torque connects force, motion, and real shaft performance.
The fastest torque estimate uses the torque constant, or Kt. This constant links torque and current. When you subtract no-load current, the remaining current contributes to useful torque. This method helps during controller tuning, drive selection, and thermal checks. It is practical when current feedback is reliable.
Torque can also come from output power and angular speed. This method is useful when you know voltage, current, motor efficiency, and RPM. It reflects the operating point. It also shows how torque changes as speed rises. At higher RPM, the same power produces less torque.
Real motors lose energy in copper, iron, switching, and bearings. This calculator includes a simple copper loss estimate from current and phase resistance. It also uses an efficiency input to estimate output power. These values support better sizing decisions. They also help compare continuous and peak operating conditions.
Many engineering systems use a gearbox. Gear reduction multiplies torque and lowers output speed. That is why a small high-speed motor can drive a heavy load. Gear efficiency still matters. A poor gearbox reduces the expected benefit. Service factor also matters because field loads are rarely ideal or constant.
Use the current method for control-focused estimates. Use the power-speed method for operating-point checks. Use auto mode when you want a conservative value. Then compare shaft torque, gearbox torque, and losses together. This creates a stronger motor selection workflow for engineering design, validation, and documentation.
Kt is the torque constant. It shows how much torque the motor produces per ampere of torque-producing current. Higher Kt means more torque for the same current.
No-load current mainly covers friction, iron loss, and internal drag. It does not fully contribute to useful output torque, so removing it improves the estimate.
Kt links current to torque. Kv links voltage to speed. They describe the same motor from different viewpoints and are often inversely related.
For a fixed power level, torque decreases as angular speed increases. That is why high-speed operation can feel weaker under the same power limit.
It can support either case. The answer depends on your current, efficiency, and service factor inputs. Use realistic thermal limits for continuous operation.
Many machines use reduction gearing. The gear ratio multiplies shaft torque, while gearbox efficiency reduces ideal output. Both values affect usable load torque.
Phase resistance supports a quick copper loss estimate using I²R. This helps engineers judge heating, efficiency changes, and the reason performance drops under load.
Choose current mode when Kt and current are trusted. Choose power mode when electrical power and RPM are known. Choose auto for a conservative estimate.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.