Wire Sizing Calculator
Static · formula-only · worked example computed when this page was built · no live data
The Wire Sizing Calculator picks the conductor size (mm²) for a load, applying continuous-load, temperature, and conduit-fill derating plus a voltage-drop check. Example: for a 50 kW 3-phase 400 V feeder, 40 m long, at 35 °C ambient, at 0.85 power factor, Design current = 84.9 A, Sizing current = 106.13 A, Conductor size = 30 mm², Derated ampacity = 108.1 A, Voltage drop = 0.94 %, Voltage-drop limit = 2 %, Breaker = 125 A (per PEC 2017 | NEC 2020 | IEC 60364-5-52 | IEC 60228).
How it works
Computed from your inputs per PEC 2017 | NEC 2020 | IEC 60364-5-52 | IEC 60228. Anything the worked example does not state uses this calculator's standard default; the interactive version shows every input and lets you change it.
Worked example (Electrical & Power)
Inputs: a 50 kW 3-phase 400 V feeder, 40 m long, at 35 °C ambient, at 0.85 power factor.
| Result | Value |
|---|---|
| Design current | 84.9 A |
| Sizing current | 106.13 A |
| Conductor size | 30 mm² |
| Derated ampacity | 108.1 A |
| Voltage drop | 0.94 % |
| Voltage-drop limit | 2 % |
| Breaker | 125 A |
Computed by WorkHive's calculation engine when this page was built; standard: PEC 2017 | NEC 2020 | IEC 60364-5-52 | IEC 60228.
How to use this calculator
- Read the worked example. It uses a 50 kW 3-phase 400 V feeder, 40 m long, at 35 °C ambient, at 0.85 power factor and shows every number in the method.
- Follow the formula with your own figures: it returns Design current, Sizing current, Conductor size, Derated ampacity, Voltage drop, Voltage-drop limit, Breaker, computed per PEC 2017 | NEC 2020 | IEC 60364.
- To compute interactively, open the Wire Sizing Calculator inside WorkHive's free Engineering Design suite (link below). It runs the same method with your inputs.
FAQ
What is an electrical wire size calculator kW?
The Wire Sizing Calculator is a free online tool that picks the conductor size (mm²) for a load, applying continuous-load, temperature, and conduit-fill derating plus a voltage-drop check. It shows the formula and a fully worked example so you can check the method, not just the number.
How is it calculated?
The result is computed from your inputs following PEC 2017 | NEC 2020 | IEC 60364. The worked example on this page shows a real computation with real numbers.
Is the calculator free?
Yes. WorkHive is free: this worked example is open to everyone, and the interactive calculator runs inside the free Engineering Design suite after a free sign-up (your work is saved to your account). WorkHive is a free, offline-first maintenance platform built for Philippine industrial plants.
Run it on your own numbers
Open the interactive Wire Sizing Calculator in WorkHive. Free, and a free sign-up saves your calculations, BOMs and scope-of-works to your account.