# DC Wire size calculator

You can use this online calculator to work out a suitable cable size (AWG, sq.mm) for both **copper** and **aluminum** wire for your solar, automotive or any other DC application.

To find the wire size, you need to specify in the calculator:

- The supply voltage DC
- The maximum acceptable voltage drop for your system
- The current (A) you expect your system to carry and finally, the length of cabling you will use for your DC application.

**Note:** This calculator uses one-way cabling! This is the length of cable from the DC power*source positive terminal to the load or appliance.*

This calculator is based on NEC Table 10, Conductor properties and refers to uncoated copper and aluminum wire at **75°C** **(167°F)**.

*For example, to supply an appliance with 3A from a 12V DC supply while keeping the maximum voltage drop to 3% over 10ft of wire, the recommended minimum wire size is 16 sq.mm.*

**Note:** The results of this calculator should only serve as a guide. We shall therefore not

accept any liability resulting from the use of this calculator. Always consult the manufacturer specification’s or a competent professional if unsure.

## How to Calculate the DC Voltage Drop

The voltage drop of a wire depends on its length, current carried and resistivity

(material size and thickness).

To calculate voltage drop in volts, use **Ohm’s law, V= I x p x l** where:

- I= current flowing in the wire
- p= resistance Ohms per 1000 ft
- l= length of the wire in ft.

To workout the DC voltage drop as a percentage, use the formula:

**Voltage drop (volts)/system voltage (12 or 24V or other voltage) x 100**.

You can also use the calculator below to workout the voltage drop for a given wire size and length carrying a known current.

*For example, the final voltage received by an appliance when you use 12ft (one-way) wire of **10 AWG supplied with 13.8V DC is 13.5 V(2% voltage drop).*

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