Use this Cable Size Calculator to determine the correct cable size based on current, voltage drop, and distance. Includes formula, example calculation, and Excel download.

What is Cable Sizing?

Cable sizing is the process of selecting the correct electrical cable cross-sectional area (mm²) to safely carry electrical current without overheating or excessive voltage drop.

Correct cable sizing ensures:

• Safe current carrying capacity
• Low voltage drop
• Protection against overheating
• Compliance with electrical standards

Cable sizing is used in:

• Residential wiring
• Industrial installations
• Electrical panels
• Motor circuits
• Distribution systems

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Cable Size Calculation Formula

The simplified cable sizing formula is:

Cable Size (mm²) = Current / Current Density

Where:

Parameter	Description
Current	Load current (Amps)
Current Density	Current per mm²

Typical values:

Material	Current Density
Copper Cable	4–6 A/mm²
Aluminium Cable	2–4 A/mm²

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Voltage Drop Formula

Cable size is also affected by voltage drop.

Voltage drop formula:

VD = (2 × L × I × R) / 1000

Where:

Symbol	Meaning
VD	Voltage drop
L	Cable length (meters)
I	Current (A)
R	Resistance
2	For single phase

For 3-phase systems:

VD = (√3 × L × I × R) / 1000

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Example Cable Size Calculation

Given:

Load Current = 100 A
Material = Copper
Current Density = 5 A/mm²

Step 1:

Cable Size = Current / Current Density
Cable Size = 100 / 5
Cable Size = 20 mm²

Step 2: Select standard cable size

25 mm² cable

✅ Recommended cable size = 25 mm²

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Standard Cable Size Table

Cable Size	Current Capacity
1.5 mm²	14 A
2.5 mm²	20 A
4 mm²	26 A
6 mm²	34 A
10 mm²	46 A
16 mm²	61 A
25 mm²	80 A
35 mm²	99 A
50 mm²	119 A
70 mm²	151 A

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Online Cable Size Calculator Logic

Inputs:

Load Current
Cable Length
Voltage
Material

Formula:

Cable Size = Current / Current Density

Calculate

Download Cable Size Calculator (Excel)

Provide a downloadable Excel calculator for engineers.

Download Cable Size Calculator Excel