Voltage drop calculator

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Voltage Drop Calculator

Length (m):

Current (Amps):




Cross section (mm²):

Voltage drop: 0.00



Voltage Drop Calculator Instructions

When dealing with solar and 12V systems, the first thing we often look at in terms of wiring is the current or amperage rating. However an area that isn't at first obvious is the voltage drop. Using the Voltage Drop Calculator the voltage drop can be calculated given the length, cross section and current. For low voltage systems the voltage drop can be quite significant meaning that some appliance won't work as expected.

The Voltage Drop Calculator is a tool which will help you determine the voltage drop and thus the impact on your system. Using a trial and error approach with the Voltage Drop Calculator you can use the Voltage Drop Calculator to help determine the cross section of the wire you need.


Length is the length in metres for the single run of wire. There's no need to think of the return wire as this is taken into account for you with the Voltage Drop Calculator.


The current is entered in amperes.

NOTE: Often when considering the wiring and the current I required, I'd look at the current rating for the wire. Keep in mind this is the maximum safe rating for the wire. Even if the wire can handle a given amperage, keep in mind the length of the wire may mean the voltage drop could mean you appliance doesn't work as expected.


The reason for including voltage in the Voltage Drop Calculator is by entering voltage, the watts is determined for you. Often devices are rated in watts. If for example you have a 12V TV that is rated at 60W, then you can either calculate this is 5A, or you can adjust the current until the watts is close to the value you want.

Cross section 

The cross section of the wire is important. It can be tricky. IF you purchase wire from a solar provider the cross section is often stated in mm such as 4mm which really means the cross section of the wire is 4 mm squared. For the Voltage Drop Calculator I use a caliper to measure the diameter of the wire and use the formula πr² to determine the cross section where r is the radius, which is half the diameter.

Be very careful with auto wire as the wire is rated in mm, but this is not the same. For auto wire the cross section will be lower.

Voltage Drop 

The voltage drop in volts is the difference you'll see between one end of the wire to the other end, for the length of the wire, drawing a given amperage, through a certain thickness of wire. If the voltage drop is too much some appliances may not work.

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The Voltage Drop Calculator comes with no warranty expressed or implied. The Voltage Drop Calculator is only for informational purposes and is not guaranteed to be error free. The information on this page is not intended to be advice.


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