12V to 48V DC Battery Cable Size Calculator Tool

Sizing your solar cables correctly is crucial for safety, performance, and efficiency. This guide will help you calculate the ideal DC cable size for your 12V, 24V, or 48V solar battery system, whether it’s for your campervan, off grid setup, or home solar installation.

Disclaimer:

This calculator is for general information and educational purposes only and does not constitute professional electrical advice. Results are estimates only and may not be suitable for all systems or installations. Electrical systems can be hazardous so always follow manufacturer instructions, relevant UK regulations, and consult a qualified professional before installation or modification.

Our DC Cable Size Calculator automatically estimates the required cable cross sectional area based on your system’s voltage, current, and cable length.

Note: A factor of 2 is already applied to the calculation to account for both the ground and live cables. The calculation assumes a copper cable is used.

IMPORTANT NOTICE:
When purchasing a cable, first check the datasheet for the recommended current and voltage rating. Then calculate voltage drop to ensure it’s below 3%

How Our Solar DC Cable Size Calculator Works

When a user inputs the current value, our calculator first checks it against preset cable ratings of up to 250 A. Only cables that can safely carry the entered current will then be considered. From these options, the calculator then calculates the voltage drop for each cable using the equation below and recommends the smallest cable size that stays within the allowable voltage drop limit.

The Formula

Voltage drop = Current x Cable Resistance
and
Cable Resistance = Resistivity x Length / Cable size

Note: The cable length refers to the total length of both live and ground.

What Is Cable Resistance

The resistance of a cable determines how much energy is lost as heat. Resistance increases with length and decreases with cable thickness (cross section).

As shown in the previous section you can estimate the cable resistance using:

Cable Resistance = Resistivity x Length / Cable size

Note: This value is usually given by the cable supplier and the lower the resistance the lower voltage drop and hence a system with higher efficiency.

Why Assuming A Copper Cable?

Copper offers low resistance, high conductivity, and excellent durability which is why it’s commonly used in many electrical systems including DC solar systems. In our calculator we assume you use a pure copper wire for your circuit connections with a resistivity of 1.68 × 10⁻⁸ Ω·m .

What Is A Voltage Drop

When electrical current flows through a cable, some energy is lost as heat, resulting in a voltage drop in the circuit. The greater the energy loss, the greater the voltage drop. This voltage drop can be measured by connecting a voltmeter directly to the battery terminals to note the battery voltage, then comparing it with the voltage measured along the cables in the system. The difference between these values represents the voltage drop. Voltage drop is directly related to the cable’s characteristics and the current flowing through the circuit. Knowing the voltage drop in a circuit is important for compliance with the BS 7671 standard, which requires it to remain below 3%.

You can read about this in our Voltage Drop Calculator post.

Further Information

Calculate Cable Size From System’s Power

If you only know your system power (kW), you can still estimate cable size:

1. Convert power to current:
   • Current = Power x Voltage
2. Input that current into our DC Cable Size Calculator along with your voltage and distance.

Example:
A 1.2kW (1200W) inverter on a 12V system draws a max current of 100A (1200/12)

For 2 m total distance, the calculator should suggest a cable of size 25 mm².

Cable mm² to AWG Conversion Table

Here’s a quick reference for converting between metric cable sizes (mm²) and AWG (American Wire Gauge) values:

Cross Section (mm²)	AWG Size	Typical Current (A)*
1.5 mm²	15 AWG	15A
2.5 mm²	13 AWG	20A
4 mm²	11 AWG	30A
6 mm²	9 AWG	40A
10 mm²	7 AWG	60A
16 mm²	5 AWG	80A
25 mm²	3 AWG	120A
35 mm²	2 AWG	150A
50 mm²	1 AWG	200A
70 mm²	00 AWG	250A

*Approximate continuous current rating for copper cables.