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).