CalcVind

Wire Size Calculator

Cable size in sq mm for your load, length and voltage drop

Load and Cable

W
m
%

A guide only. Have a licensed electrician confirm sizes and MCBs.

Suggested Wire Size

4 sq mmWire size
14.49 ALoad current
3.88 V (1.69%)Voltage drop
2.25 sq mm
Minimum for voltage drop
4 sq mm
Minimum for current

Commonly used copper wire sizes in homes

WireUsual MCBTypical use
1 sq mm6 ALighting
1.5 sq mm10 ALights and fans
2.5 sq mm16 APower sockets, 1–1.5 ton AC
4 sq mm20 AGeyser, 2 ton AC, kitchen
6 sq mm32 AHeavy loads, sub-mains
10 sq mm40 ASub-main to a floor
16 sq mm63 AMain supply
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  1. 1
    Enter the load
    Total watts on the circuit
  2. 2
    Add cable length and drop
    One-way length, usually 3%
  3. 3
    Get the wire size
    In sq mm, with the reasoning

How is wire size chosen?

A wire must carry the current without overheating, and be thick enough that the voltage doesn't drop too much over its length. The calculator takes the larger of the two needs.

Current I = P ÷ (V × PF) (three-phase: ÷ √3 V × PF)

Area for drop = (2 or √3) × ρ × length × I ÷ allowed volt drop

Voltage drop

Long runs lose voltage in the wire itself. Keeping the drop within about 3% for lighting and 5% for other loads keeps motors, ACs and electronics working well. Doubling the length doubles the drop, so long runs often need a bigger size than the current alone suggests.

Current rating

The current a wire can safely carry depends on its insulation, how it's laid (in conduit, bunched, clipped) and the room temperature, as set out in IS 3961. Use the manufacturer's datasheet for your wire and make sure the MCB rating is below the wire's rating.

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Frequently asked questions

Which wire is used for a 1.5 ton AC?

Typically 2.5 sq mm copper on a 16 A circuit for short runs; long runs or 2 ton units often use 4 sq mm on 20 A. Follow the AC maker's installation guide.

Is aluminium wire OK for homes?

Copper is preferred inside homes. Aluminium is used for service lines and large feeders, and needs about 1.6 times the cross-section of copper for the same current.

Is the length one way or both ways?

One way. The formula already accounts for current flowing out and back.

Sources

Last reviewed: October 2026