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Wire Size Calculator: Cable sq mm for Copper and Aluminium

Enter the load (watts or amps), supply, cable length and conductor. You get the smallest standard cable that carries the current safely and keeps voltage drop within your limit, plus the MCB size.

Cable size

2.5mm²

Load current
14.5 A
MCB rating
16 A
Cable rating after derating
20.9 A
Voltage drop
5.22 V · 2.27%

For guidance only. Electrical work must follow IS 732 and the cable makers’ tables, and be done or checked by a licensed electrician.

Copper, PVC, single-core in conduit (IEC 60364-5-52, method B1), derated for temperature and grouping.

Show working
  1. I = 3,000 ÷ (230 × 0.9) = 14.49 A
  2. MCB ≥ I → 16 A
  3. 16 ÷ (0.87 × 1) = 18.4 A → 2.5 mm² (24 A)
  4. ΔV = 2 × 20 × 14.49 × 0.0225 ÷ 2.5 = 5.22 V

How to use

  1. Enter the load in watts (with power factor) or the current in amps.
  2. Choose single- or three-phase, voltage, cable length and copper or aluminium.
  3. Check ambient temperature, circuits in the same conduit and drop limit under More options.

Good to know

Method: design current → next standard MCB (6, 10, 16, 20, 25, 32 A …) → the cable must carry at least the MCB rating after derating, and the voltage drop must stay within your limit. Ratings are from IEC 60364-5-52 for PVC-insulated single-core cables in conduit on a wall (method B1), corrected for ambient temperature and grouping.

Indian homes often see 40 °C or more in ceilings and walls, so the default derating is for 40 °C (factor 0.87). Bunching several circuits in one conduit lowers the rating further (2 circuits × 0.80, 3 × 0.70). Voltage drop uses ρ = 0.0225 Ω·mm²/m for hot copper and 0.036 for aluminium.

Safety: this is a guide, not a design. Cables in India must meet IS 694 (PVC-insulated cables), wiring must follow IS 732 and the Central Electricity Authority safety regulations, and makers publish their own current tables. Common practice is at least 1.5 sq mm copper for lights and fans and 2.5 sq mm for 16 A power sockets; get a licensed electrician to choose and install cables.

Questions

Which wire for a 16 A socket?

Usually 2.5 sq mm copper on a 16 A MCB for short runs; longer runs may need 4 sq mm to limit voltage drop.

Which wire for a 1.5 ton AC?

An AC draws about 7–10 A; most electricians use 2.5 sq mm copper on a 16 A MCB, or 4 sq mm for long runs.

Which wire for a 2 kW or 3 kW geyser?

3 kW at 230 V is about 13 A: 2.5 sq mm copper on a 16 A MCB for normal lengths.

Why does length matter?

Long cables drop voltage. The tool upsizes the cable until the drop is within your limit (3% by default).

Can I use aluminium wire at home?

Most new home wiring in India uses copper. Aluminium needs larger sizes and proper lugs; follow your electrician and local rules.

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