Copper cable size (mm²) and breaker for a load, checked for current and voltage drop.
How this works
Current I = watts / volts. Voltage drop for single phase copper = 2 x length x I x 0.0175 / area (mm²), kept under 3%. Rough current ratings in conduit: 1.5 mm² 15 A, 2.5 mm² 20 A, 4 mm² 27 A, 6 mm² 34 A, 10 mm² 46 A, 16 mm² 61 A.
Questions people ask
How do I use the Wire Size for Load tool?
Fill in the fields, starting with “Load”, “Supply voltage” and “Cable length (one way)”, and change any other options that match your home. The answer, a drawing and practical tips update as you type, and the Copy link button saves your numbers in a link you can share.
Is the Wire Size for Load tool free?
Yes. The Wire Size for Load tool is free, with no sign-up, and works on phones, tablets and computers. The results are estimates to help you plan, so check with a qualified professional before structural, electrical, gas or plumbing work.