VFD Sizing Calculator
Free VFD Sizing Calculator and Inverter Selection Tool
Welcome to Drive Outlet Megastore’s Free VFD Sizing Calculator
Choosing the correct variable frequency drive (VFD) is critical for reliable motor control and system efficiency.
Our simple and fast VFD sizing calculator helps you quickly estimate the correct inverter size for your motor application.
Whether you’re replacing an old drive, upgrading, or specifying a new project, this VFD selection calculator makes it easy.
How to Use the Inverter Calculator
- Enter Motor Power (kW or HP)
- Find the rated motor power on the nameplate, usually shown in kW or HP.
- If unknown, see the guide below on how to estimate it.
- Select Motor Voltage
- Most common voltages are 230V, 400V, 415V, or 480V.
- Motor nameplates usually clearly state this.
- Choose Load Type
- Normal Duty: Fans, pumps, blowers — low starting torque.
- Heavy Duty: Conveyors, crushers, mixers — require higher starting torque.
- (Optional) Add Notes
- For example: “high starting load”, “frequent start/stop”, “outdoor use”.
- Calculate
- Instantly see the recommended inverter power rating, output current, and load type guidance.
How to Find Motor Details
How to Find the Motor Voltage:
- Check the motor nameplate — usually lists rated voltage, e.g., 400V, 415V, 480V.
- It may also show multiple voltages (e.g., “220/400V” or “230/460V” for dual voltage motors).
- If no nameplate:
- Check motor supply documents.
- Check the panel where the motor is connected — supply voltage often matches.
- Measure voltage with a multimeter (only a qualified person should do this).
How to Find the Motor Power (kW or HP):
- On the nameplate: look for “Rated Power,” “Output,” or “Motor Power” listed in kW or HP.
- If no nameplate:
- Use motor frame size and shaft diameter charts to estimate (contact us if you need help).
- If you know full load current (Amps) and voltage, estimate using: Motor kW ≈ (Voltage × Current × √3 × Efficiency) ÷ 1000
- Assume ~90% efficiency for standard motors.
Understanding Load Types
Choosing the correct load type is important for drive selection:
| Load Type | Examples | Description |
|---|---|---|
| Normal Duty | Fans, Pumps, Blowers | Steady loads with low torque at start-up |
| Heavy Duty | Conveyors, Crushers, Mixers | High starting torque, frequent start/stop cycles |
If you are unsure, it’s safest to select Heavy Duty to ensure reliable operation.
