Wire Size Calculator
Fill in the values and the answer updates as you type.
How the Wire Size Calculator works
Minimum area = k × resistivity × length × current ÷ (supply voltage × allowed drop). The result is rounded up to the next common metric cable size. This checks voltage drop only; the cable must also be rated for the current (ampacity) and the installation method. Example: with the default values, minimum cross-section comes to 5.07 mm².
Inputs and results
The Wire Size Calculator takes 6 inputs and gives 3 results.
What you enter
- Load current (A) — starts at 25.
- One-way cable length (m) — starts at 40.
- Supply voltage (V) — starts at 230.
- Maximum voltage drop (%) — starts at 3.
- Conductor material — starts at Copper. Choose from: Copper and Aluminium.
- Supply type — starts at Single-phase. Choose from: Single-phase and Three-phase.
What you get
- Minimum cross-section (mm²)
- Standard size (mm²)
- Voltage drop at standard size
Example: Wire Size Calculator with the starting values
With load current 25 A, one-way cable length 40 m, supply voltage 230 V, maximum voltage drop 3 % and conductor material Copper, the calculator returns:
| Minimum cross-section (mm²) | 5.07 |
|---|---|
| Standard size (mm²) | 6 |
| Voltage drop at standard size | 2.54% |
Change any value above and the results update straight away.
Wire Size Calculator FAQ
How do I use the Wire Size Calculator?
Enter load current, one-way cable length, supply voltage and maximum voltage drop in the fields, then read minimum cross-section (mm²), standard size (mm²) and voltage drop at standard size in the result panel. The answer updates as you type, and you can press Calculate or Enter to refresh it. Use “Copy link” to share your exact numbers with someone else.
What does the Wire Size Calculator calculate?
Minimum cable cross-section for an allowed voltage drop. It returns minimum cross-section (mm²), standard size (mm²) and voltage drop at standard size from the 6 values you provide.
What values does the Wire Size Calculator start with?
It opens with load current 25 A, one-way cable length 40 m, supply voltage 230 V and maximum voltage drop 3 % so you can see a working result straight away. Replace them with your own numbers, or press Reset to return to these starting values.
Is the Wire Size Calculator free and private?
Yes. It is free, needs no account, and runs in your browser, so nothing you type is sent to or stored on our servers. See the Privacy Policy for details.
Can I rely on the Wire Size Calculator for important decisions?
Treat the result as a well-rounded estimate. Real situations often have details a general calculator cannot know, so confirm important decisions with a qualified professional. See the Disclaimer for more.