Free Engineering Tool
Motor Sizing Calculator
Calculate required motor power from load parameters and get recommended standard IEC motor size with starting current and torque estimates.
Motor Selection
Motor Power Calculation
IEC Standard Motor Sizes (kW)
| Range | Available Sizes (kW) |
|---|---|
| Small | 0.37, 0.55, 0.75, 1.1, 1.5, 2.2, 3.0, 4.0 |
| Medium | 5.5, 7.5, 11, 15, 18.5, 22, 30, 37 |
| Large | 45, 55, 75, 90, 110, 132, 160, 200, 250, 315 |
Starting Current Multipliers
- DOL — 6–8× rated current
- Star-Delta — 2–3× rated (÷3 of DOL)
- Soft Starter — 2–4× rated
- VFD — 1–1.5× rated
ℹ️ Tip: Always select the next standard size above the calculated requirement. Oversizing by one step provides thermal margin and longer bearing life.
Service factor (SF) accounts for operating conditions beyond rated values. Use 1.0 for ideal conditions, 1.15 for moderate ambient or occasional overloads, 1.25 for harsh environments, and 1.5 for severe duty with frequent starts or high-inertia loads.
Constant torque loads (conveyors, positive displacement pumps) require the same torque regardless of speed — power is proportional to speed. Variable torque loads (centrifugal fans/pumps) have torque proportional to speed² and power proportional to speed³ — they need much less power at reduced speed.
Motors are only made in standard sizes. You must always select the next standard size up. Additionally, slight oversizing (10-15%) provides thermal headroom, compensates for voltage variations, and extends bearing life.
Use a VFD when: (1) variable speed is needed, (2) soft starting is required, (3) energy savings on variable torque loads are important, (4) the power supply cannot handle DOL starting current. VFDs also reduce mechanical stress on couplings and driven equipment.
The procedures described on this page were developed and field-tested by the Vibromera team using the Balanset-1A, a portable dual-channel balancer and vibration analyzer for on-site rotor balancing.
Balance motors on-site, diagnose electrical and mechanical faults.
Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
