How to calculate cable cross-section size?

Cable cross-section is calculated using A = (k × ρ × I × L) / V_drop, where k is a system factor (2 for single-phase/DC, √3 for three-phase), ρ is conductor resistivity, I is current in amps, L is one-way cable length in meters, and V_drop is the allowable voltage drop in volts.

Why is voltage drop important in cable sizing?

Excessive voltage drop causes equipment to receive less than rated voltage, leading to poor performance, overheating of motors, dimming of lights, and potential equipment damage. Most standards recommend limiting voltage drop to 3-5% of supply voltage.

What is the difference between copper and aluminum cables?

Copper has lower resistivity (0.0175 Ω·mm²/m) than aluminum (0.0283 Ω·mm²/m), meaning copper cables can carry the same current with a smaller cross-section. However, aluminum is lighter and cheaper. Aluminum requires about 1.6× the cross-section of copper for the same current capacity.

What are standard cable sizes?

Standard cable cross-sections per IEC 60228 are: 0.75, 1.0, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185, 240, and 300 mm². The calculated cross-section should always be rounded up to the next standard size.

How to convert AWG to mm²?

Common conversions: 14 AWG ≈ 2.08 mm², 12 AWG ≈ 3.31 mm², 10 AWG ≈ 5.26 mm², 8 AWG ≈ 8.37 mm², 6 AWG ≈ 13.3 mm², 4 AWG ≈ 21.2 mm², 2 AWG ≈ 33.6 mm², 1/0 AWG ≈ 53.5 mm², 4/0 AWG ≈ 107 mm².

Free Engineering Tool

Cable Cross-Section Calculator

Determine the correct wire size (mm²) based on current, cable length, voltage, and allowable voltage drop. Round up to nearest standard IEC size automatically.

IEC 60228 Cu & Al mm² & AWG

Current (A)

Cable Length (m, one-way)

Voltage (V)

System Type

Max Voltage Drop (%)

Conductor Material

Quick presets

Results

Required Standard Cable Size

—

Calculated Cross-Section (exact)

—

Actual Voltage Drop (standard size)

—

Voltage Drop Percentage

—

AWG Equivalent

—

Cable Cross-Section Formula

The minimum required conductor cross-section to stay within the allowable voltage drop is:

k — system factor: 2 for single-phase AC and DC, √3 for three-phase AC
ρ — resistivity of conductor (Ω·mm²/m): Cu = 0.0175, Al = 0.0283
I — current (A)
L — one-way cable length (m)
V_drop — allowable voltage drop (V)

Allowable Voltage Drop

Actual Voltage Drop

Once a standard cable size A_std is selected:

Standard Cable Sizes (IEC 60228)

mm²	AWG (approx.)	mm²	AWG (approx.)
0.75	18 AWG	25	4 AWG
1.0	17 AWG	35	2 AWG
1.5	15 AWG	50	1/0 AWG
2.5	13 AWG	70	2/0 AWG
4	11 AWG	95	3/0 AWG
6	9 AWG	120	4/0 AWG
10	7 AWG	150	300 MCM
16	5 AWG	185	350 MCM

Practical Example

Example — Single-phase 230V Circuit

Given: I = 10 A, L = 30 m, V = 230 V, max drop = 3%, copper

V_{drop(allowed)} = 230 × 3/100 = 6.9 V

A = 2 × 0.0175 × 10 × 30 / 6.9 = 1.52 mm²

Standard size: 2.5 mm² (rounded up)

Actual V_drop = 2 × 0.0175 × 10 × 30 / 2.5 = 4.2 V = 1.83%

⚠️ Note: This calculator sizes cable based on voltage drop only. Always verify that the selected cable size also meets the current-carrying capacity (ampacity) requirements per local electrical codes (e.g., IEC 60364, NEC).

Cable cross-section is calculated using the formula: A = (k × ρ × I × L) / V_drop, where k is a system factor (2 for single-phase/DC, √3 for three-phase), ρ is the conductor resistivity, I is current, and L is one-way cable length.

The calculated value should be rounded up to the next standard IEC 60228 size to ensure the actual voltage drop stays within limits.

Excessive voltage drop causes equipment to receive less than its rated voltage, leading to:

Motor overheating and reduced torque
Dimming or flickering of lights
Malfunction of sensitive electronic equipment
Increased energy losses in the cable

Most electrical codes (IEC 60364, NEC) recommend keeping voltage drop below 3–5% from the supply point to the load.

Copper (ρ = 0.0175 Ω·mm²/m) has lower resistivity than aluminum (ρ = 0.0283 Ω·mm²/m), meaning copper cables need smaller cross-sections for the same current. However:

Copper: Better conductivity, smaller size, easier to terminate, longer life
Aluminum: Lighter weight (~30% of copper), significantly cheaper, preferred for large power distribution

For the same current capacity, aluminum requires approximately 1.6× the cross-section of copper.

Standard cable cross-sections per IEC 60228 are:

Small: 0.75, 1.0, 1.5, 2.5, 4, 6 mm²
Medium: 10, 16, 25, 35, 50 mm²
Large: 70, 95, 120, 150, 185, 240, 300 mm²

Always round up the calculated cross-section to the next standard size — never round down.

Common AWG to mm² conversions:

14 AWG ≈ 2.08 mm² (closest standard: 2.5 mm²)
12 AWG ≈ 3.31 mm² (closest standard: 4 mm²)
10 AWG ≈ 5.26 mm² (closest standard: 6 mm²)
8 AWG ≈ 8.37 mm² (closest standard: 10 mm²)
6 AWG ≈ 13.3 mm² (closest standard: 16 mm²)
4 AWG ≈ 21.2 mm² (closest standard: 25 mm²)
2 AWG ≈ 33.6 mm² (closest standard: 35 mm²)
1/0 AWG ≈ 53.5 mm² (closest standard: 50 mm²)
4/0 AWG ≈ 107 mm² (closest standard: 120 mm²)

The formula is: mm² = 0.012668 × 92^{((36−AWG)/19.5)}

The procedures described on this page were developed and field-tested by the Vibromera team using the Balanset-1A, a portable dual-channel balancer and vibration analyzer for on-site rotor balancing.