How do I calculate cable size in India?

Cable size (sq mm) = (Current × Cable Length × 2) / (Conductivity × Allowable Voltage Drop). For copper cables, conductivity is 56 S·m/mm². Always round up to the next standard cable size.

What cable size is needed for a 15 amp load in India?

For a 15 amp load in India, a 2.5 sq mm copper cable is generally sufficient for short runs up to 20 metres. For longer runs or higher voltage drop sensitivity, use 4 sq mm cable.

What is the standard voltage drop allowed in India?

As per IS 732, the allowable voltage drop for electrical installations in India is 3% for lighting circuits and 5% for power circuits from the source to the point of utilisation.

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Cable Size Calculator

India · IS 732 · sq mm · Single & 3-Phase

Supply Type

Calculation Method

Load Power (Watts)

Cable Length – One Way (metres)

Allowable Voltage Drop (%)

Conductor Material

Power Factor

Recommended Cable Size

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Cable Size Calculator India – Electrical Wire Size in sq mm

Our cable size calculator helps electricians, electrical engineers, and contractors in India select the correct cable cross-section in sq mm based on load, cable length, and allowable voltage drop as per IS 732.

Supports single phase (230V) and three phase (415V) systems. Works for both copper and aluminium conductors.

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Cable Size Formula (IS 732)

Current (A) = Power (W) / (Voltage × Power Factor)
For 3-phase: Current = Power / (√3 × 415 × PF)

Cable Size (mm²) = (2 × I × L) / (σ × V_drop)
Where σ = conductivity (56 for Cu, 35 for Al)
V_drop = Voltage × Allowable Drop %

2000W load, single phase, 20m cable, 5% VD, copper:
Current = 2000 / (230 × 0.9) = 9.66 A
V_drop allowed = 230 × 0.05 = 11.5V
Cable = (2 × 9.66 × 20) / (56 × 11.5) = 0.60 mm²
Standard size → 1.5 sq mm cable

Standard Cable Sizes in India

1.0 sq mm

~10 A

1.5 sq mm

~15 A

2.5 sq mm

~20 A

4 sq mm

~25 A

6 sq mm

~32 A

10 sq mm

~43 A

16 sq mm

~57 A

25 sq mm

~75 A

35 sq mm

~92 A

50 sq mm

~110 A

Frequently Asked Questions

For a 3-phase motor: Current = kW × 1000 / (√3 × 415 × efficiency × power factor). Use 125% of full load current for cable sizing to handle starting currents. Then apply the voltage drop formula to confirm the size.

A 5-ton (18,000W) single-phase AC unit at 230V with 0.85 PF draws approximately 92 amps. A 25 sq mm or 35 sq mm copper cable would be required depending on cable run length and installation method.

IS 732 specifies 3% maximum voltage drop for lighting circuits and 5% for power circuits, measured from the supply point to the point of utilisation in low voltage installations.

Copper cables are preferred for internal wiring and small installations due to their higher conductivity, flexibility, and smaller size. Aluminium cables are commonly used for large power distribution (above 16 sq mm) due to lower cost, but require larger cross-sections for the same current capacity.

Cable Size Calculator India – Electrical Wire Size in sq mm

Cable Size Formula (IS 732)

Standard Cable Sizes in India

Frequently Asked Questions

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