Size on the amps stamped on the nameplate. Service factor is a protection envelope, never a sizing input.
Over 100 ft, investigate output filters and ensure the use of VFD rated cable.
Measure at the air intake, door closed. Reference 104 °F.
Site elevation, not the level inside the building. Reference 3281 ft.
Often raised at commissioning to quiet motor noise. That choice must show up in sizing.
* Sizing is on a normal duty basis. The overload is carried in this factor: variable torque holds 110 percent, and constant torque holds 150 percent as the 1.5 multiplier. To size from the drive's heavy duty column instead, keep this on variable torque so the overload is not counted twice.
* Below base speed, motor current rises with the square of speed. Above base speed, with voltage capped, it rises with the cube. At 1.67x base the load can demand roughly 4.63x the base current, which can exceed motor FLA, and the motor can reach a torque limit before the drive does. Check motor capability first. Behavior varies by VFD brand, so use with caution. Leave this at 60 if you are unsure.
Required continuous drive current
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Normal duty continuous rating
Enter a nameplate FLA to begin.
Why size for reliability
Traditional sizing matches the drive to the motor current and stops there. It picks the smallest frame that carries the amps under good conditions, and that drive runs fine at commissioning. It also runs close to its thermal limit for the rest of its life. Inverter temperature is the strongest predictor of how fast a drive ages, and output current is the next strongest. A drive sized to the edge starts aging the day it is energized.
Reliability sizing adds what the installation does to the drive. The cable run, the cabinet temperature, the altitude, the carrier frequency, the load class, the inertia, the low speed cooling, and the overspeed each take back margin you assumed was there. The required current comes out higher because the drive has to survive the installation, not only match the motor.
The larger frame does cost more, often a few hundred to a couple thousand dollars. Weigh that against a failure. When a drive trips on a running line you pay for the drive, the service call, the labor, and the production lost while the line sits idle. Put a real number on one hour of downtime on your line. For most plants that hourly figure is far larger than the price of the next frame up, and a single avoided failure pays for the margin many times over.
This is the whole reason the framework exists. VFDs do not fail. Installations fail them. Sizing with margin keeps the installation from becoming the thing that fails.
This tool runs the ORCA-Size method, set out in full in the paper that introduced it: ORCA-Size: A Reliability-Focused Alternative to Traditional Variable Frequency Drive Sizing, Carl Lee Tolbert, TechRxiv, 2026.
This tool is for educational purposes only. It returns a first pass estimate using the ORCA-Size lookup factors and is not a substitute for an engineered drive selection. Verify every result against the specific drive's published derating data, the motor nameplate, and your local code. Confirm the final selection with your distributor before you order.