How to size battery cables | both gauge (AWG) and length for your DC applications
Use this free calculator to easily work-out the size (gauge) of cable for your battery bank connections for
inverters and DC appliances.
Battery cable size (gauge) calculator
The battery cable size depends on:
- how much current your appliances draw
- the length of cable from the battery to the appliances and
- what voltage drop is acceptable (usually up to 3%)
The longer the cable or larger the current drawn by the appliances, the thicker or lower gauge number you will need to safely connect to the batteries.
Worked examples: How to size battery cables using the calculator
1. Sizing cable connections from the battery bank to an inverter
Step 1: Work out the current draw by the inverter
The current draw by the inverter from the battery bank can be found from the formula: I=p÷v, where,
- p is the inverter power rating
- v is the battery bank voltage.
Step 2: Next, input your desired battery cable length (one-way!) and finally acceptable voltage drop (default is usually 3%).
For example, if the inverter power rating is 1000 W and connects to a 12 V DC battery, then the current draw by the inverter = 1000÷12 = 83.3 A.
If the desired one-way cable length is 10 ft and acceptable voltage drop is 3%, then the minimum cable gauge is #3, see screenshot below.
Table: Battery cable sizes for selected inverter sizes (watts)
Inverter specifications (W)
Wire gauge (AWG)
2. Sizing cable connections from the battery bank to DC appliance
Step 1: Work out the current draw by the appliance
The current draw by the appliance from the battery bank can be found from the formula: I=p ÷ v, where:
- p is the appliance’s power consumption (W) and
- v is the battery bank voltage.
Step 2: Next, input your desired one-way cable length, and acceptable voltage drop.
For example, if the DC fridge rating is 100 W and connects to a 12 VDC battery, then the current draw by the inverter = 100÷12 = 8.3 A.
If the desired one-way cable length is 20 ft and acceptable voltage drop is 3%, then the minimum cable gauge to use is #10, see screenshot from the calculator below.
Which material to use for Battery cable
When connecting the batteries in the battery bank and the load, check to make sure that the cables are made from copper and not copper clad aluminum (CCA). Copper cable results in less wastage of power (lower voltage drop) especially for long cable runs.
Tips for sizing battery cables
- Always size for maximum current draw you expect for draw from the battery. Work out the total power consumption of all the appliances you expect to connect to the battery.
This way, you will avoid damage to the cable should you connect additional appliances later.
- Use Higher rated voltage inverters: When dealing with high power inverters e.g. 1000 W and above, when possible use higher voltage rated inverters, 24V, 48V… instead of 12V. The currents drawn are much lower and less costly wire gauges (higher AWG) can be used. 41.6 A from 1000W/24 is much safer to work
with than 83.3 A from 1000W/12!
How to workout battery cable length for a set voltage drop
Occasionally, you may want to know the maximum cable length of a wire gauge that can carry a current while limiting the voltage drop to a certain threshold.
In this case, you can use the battery cable length calculator or table below to find the maximum length of cable (one-way) to carry a current for a set voltage drop.
Battery cable length calculator
For example, what is the maximum length of #6 cable that can carry 20 A with a voltage drop of 2%?
Using the calculator above, the estimated one-way cable length is 12 ft. If you desire to work with a longer cable, consider: increasing the cable size (lower AWG).
AWG Cable size