Use this BLDC motor power calculator to find electrical input power from voltage and current or mechanical shaft power from torque and RPM. View results instantly in watts, kilowatts, or horsepower.
Assumptions & Formulas
– This mode calculates the total electrical power drawn by the motor from the power source.
– Formula: Power = Voltage × Current
Note: Results are mathematically precise based on inputs and are rounded to 2 decimal places. 1 HP = 745.7 Watts. 1 kW = 1000 Watts.
This BLDC motor power calculator calculates electrical input power using voltage $\times$ current, or mechanical shaft power using torque $\times$ RPM / 9.5488. Once the calculation is complete, it will automatically convert your final result into watts, kilowatts, and horsepower.
The term “BLDC motor power” can refer to several different things depending on your specific project. This tool covers the two most practical measurements you will need: the input electrical demand required to run the motor, and the physical shaft output it delivers.
What does BLDC motor power mean?
When users search for a motor power calculator, they are usually trying to figure out one of a few specific numbers. They might need the electrical input power drawn from a battery to size their wiring. Alternatively, they might need the mechanical output power delivered at the shaft to match a drivetrain. Sometimes, they are simply trying to verify the manufacturer-rated power or find the horsepower derived from torque and RPM.
This calculator does not calculate datasheet rated power, nor does it calculate overall system efficiency. Instead, it calculates the selected power value directly based on the real-world numbers you enter into the tool.
What this BLDC motor power calculator calculates
The tool features two distinct calculation modes depending on the data you currently have available and the specific problem you are trying to solve.
| Calculator mode | What it calculates | Inputs used | Output units |
|---|---|---|---|
| Electrical Input Power | Power drawn from the source | Supply voltage, motor current | W, kW, HP |
| Mechanical Shaft Power | Power delivered at the shaft | Motor torque, motor speed | W, kW, HP |
To make the process as seamless as possible, it handles the following specific inputs and units:
| Input | Supported unit(s) |
|---|---|
| Voltage | V |
| Current | A, mA |
| Torque | Nm, kg-cm, lb-ft, oz-in |
| Speed | RPM |
BLDC motor power formulas used in this calculator
The calculator relies on two standard engineering formulas. The math it applies depends entirely on the active mode you choose.
Electrical input power$$P = V \times I$$
This first formula is used when you want to know how much electrical power the motor system is drawing based on the values entered.
Mechanical shaft power$$P(W) = \dfrac{T \times RPM}{9.5488}$$
This second formula is used when you want to know how much mechanical shaft power corresponds to the entered torque and RPM.
Electrical input power vs mechanical shaft power
Electrical input power represents the total electrical energy entering the motor system at the supply side. Mechanical shaft power represents the physical rotational force delivered at the output side.
In practical setups, output power is typically lower than input power. This difference occurs because energy is naturally lost to electrical resistance in the windings, magnetic inefficiencies, and mechanical friction in the bearings.
How to calculate motor power from voltage and current
To find your electrical power demand, you simply multiply the supply voltage by the current. This tells you the total electrical load the motor is placing on your system.
Formula: $$P = V \times I$$
Example calculation:
If you have a 48 V system drawing 20 A of current, you multiply 48 by 20 to get 960 W. That equals 0.96 kW, or roughly 1.29 HP.
Keep in mind that this represents the electrical input power going into the system, which is not necessarily the mechanical shaft power coming out.
How to calculate motor power from torque and RPM
To find the mechanical power, you multiply the torque by the motor speed, and then divide by the constant 9.5488. Both torque and speed are required for this math because mechanical power is a measure of rotational force applied over a specific amount of time.
Formula: $$P(W) = \dfrac{T \times RPM}{9.5488} $$
Example calculation:
If your motor generates 2.5 Nm of torque at a speed of 3000 RPM, you multiply 2.5 by 3000 to get 7500. Divide that by 9.5488, and you get about 785.44 W. That converts to roughly 0.79 kW, or about 1.05 HP. This represents the physical shaft output power based on the torque and speed provided.
When should you use electrical power and when should you use shaft power?
Select the electrical input power mode for tasks like battery sizing, checking maximum current draw, verifying electronic speed controller (ESC) load, and evaluating wiring capacity.
Select the mechanical shaft power mode for tasks like sizing drivetrains, matching gearboxes, analyzing torque-speed performance, and comparing the physical output between different motors.
BLDC motor power unit conversions
Rather than making you do the math by hand, the tool handles all unit scaling automatically to save you time.
| Conversion | Value |
|---|---|
| 1 kW | 1000 W |
| 1 HP | 745.7 W |
| 1 A | 1000 mA |
| W to kW | divide by 1000 |
| W to HP | divide by 745.7 |
Torque unit conversions supported by this calculator
Because motors are sourced globally, torque specifications often arrive in several different formats. The calculator automatically converts all of your torque inputs to Newton-meters (Nm) in the background before applying the mechanical shaft power formula.
| Torque unit | Equivalent to Newton-meters (Nm) |
|---|---|
| 1 Newton-meter (Nm) | 1 Nm |
| 1 Kilogram-centimeter (kg-cm) | $\approx$ 0.09807 Nm |
| 1 Pound-foot (lb-ft) | $\approx$ 1.3558 Nm |
| 1 Ounce-inch (oz-in) | $\approx$ 0.00706 Nm |
Horsepower, watts, and kilowatts for BLDC motors
Watts are the fundamental base output of both power formulas used in this tool. Kilowatts are simply a larger metric expression of that exact same power, making it easier to read large numbers. Horsepower serves as a common alternative unit for comparing motor and engine output across different industries.
Your calculator converts between all three automatically so you can use the value that fits your needs.
| Power unit | Best for |
|---|---|
| Watts (W) | Smaller motors, electronics, and precise numeric values |
| Kilowatts (kW) | Larger motor ratings, EVs, and overall system power |
| Horsepower (HP) | Automotive applications, workshop tools, and general motor comparison |
Common motor power examples by voltage, current, torque, and RPM
Here is a helpful reference table showing typical power values across a range of common motor setups, calculated using both input and shaft methods.
| Calculation Mode | Input Values | Power in W | Power in kW | Power in HP |
|---|---|---|---|---|
| Input Power | 12 V, 5 A | 60 W | 0.06 kW | 0.08 HP |
| Input Power | 24 V, 15 A | 360 W | 0.36 kW | 0.48 HP |
| Input Power | 48 V, 30 A | 1440 W | 1.44 kW | 1.93 HP |
| Input Power | 72 V, 50 A | 3600 W | 3.60 kW | 4.83 HP |
| Shaft Power | 0.5 Nm, 1500 RPM | 78.5 W | 0.08 kW | 0.11 HP |
| Shaft Power | 2.0 Nm, 3000 RPM | 628.4 W | 0.63 kW | 0.84 HP |
| Shaft Power | 5.0 Nm, 4000 RPM | 2094.5 W | 2.09 kW | 2.81 HP |
| Shaft Power | 10.0 Nm, 5000 RPM | 5236.3 W | 5.24 kW | 7.02 HP |
How to use this BLDC motor power calculator
Using the tool is straightforward. First, choose the calculation method that fits your goal—either electrical input or mechanical shaft power. Next, enter the required values for that specific method. Be sure to select your specific unit from the dropdown menus, such as choosing between amps or milliamps for current, or selecting your preferred torque unit. The tool will instantly read out the resulting power in watts, kilowatts, or horsepower. You can easily switch methods if you want to compare your electrical input with your mechanical output.
What this calculator does not calculate
To ensure clarity about how the math works, here are the things this tool is not designed to do:
- It does not calculate overall motor efficiency.
- It does not calculate datasheet rated power.
- It does not calculate peak burst power.
- It does not calculate power-to-weight ratios.
- It does not estimate battery runtime.
- It does not calculate AC three-phase power equations.
Input limits and validation rules
For the mathematical models to work properly and provide accurate results, your voltage, current, torque, and RPM must all be greater than zero. The tool only validates the selected calculation mode at one time. Any numbers left in the inactive fields do not affect the final result until you actively switch over to that specific mode.
BLDC motor power calculator FAQs
How do you calculate BLDC motor power?
You calculate BLDC motor power using either voltage and current or torque and RPM. To find the electrical input power, multiply the supply voltage by the current. To find the mechanical shaft power, multiply the motor’s torque by its RPM, then divide by 9.5488.
Is BLDC motor power the same as shaft power?
No, BLDC motor power is a broad term that is not always the same as shaft power. It can refer to either the electrical energy going into the motor or the mechanical shaft power coming out of it.
How do you calculate motor power from voltage and current?
Multiply the supply voltage by the total motor current. For example, if a motor draws 10 amps from a 24-volt battery, the electrical input power is 240 watts.
How do you calculate motor power from torque and RPM?
Multiply the motor’s torque in Newton-meters by its rotational speed in RPM, then divide that product by 9.5488. This mathematical constant ensures your rotational force and speed are accurately converted into watts.
How do you convert motor watts to horsepower?
Divide your total wattage by 745.7 to convert watts to horsepower. Since one mechanical horsepower is universally equivalent to 745.7 watts, this simple division gives you an accurate HP rating.
What is the difference between motor input power and output power?
Input power is the electrical energy consumed from the power source, while output power is the physical mechanical force delivered at the shaft. In the real world, output power is typically lower than input power due to operational losses like friction and heat.
Which torque units can this calculator use?
You can enter your torque values in Newton-meters (Nm), kilogram-centimeters (kg-cm), pound-feet (lb-ft), or ounce-inches (oz-in). The calculator automatically converts any non-standard metric or imperial inputs into Newton-meters behind the scenes.
Does this calculator calculate motor efficiency?
No, this calculator does not evaluate motor efficiency. It calculates pure input power or pure output power based strictly on the raw numbers you provide, without estimating thermal losses or mechanical friction.
Can I use this calculator for horsepower from torque and RPM?
Yes, you can calculate horsepower directly from torque and RPM. Simply select the Mechanical Shaft Power mode, enter your numbers, and the tool will allow you to read the resulting mechanical output in horsepower.
What unit should I use for BLDC motor power: W, kW, or HP?
Use watts for small hobby motors, kilowatts for larger system ratings, and horsepower when comparing to traditional engines. The right unit simply depends on the scale of your application.
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