⚡ Electrical
Voltage Drop Calculator
Wire has resistance, and the longer or thinner it is the more of your supply it eats. The drop is calculated over the round trip because current has to travel out and back, which is why a long run reacts so badly to a small gauge. The usual design target is under 3% for a branch circuit and under 5% overall.
How it works
Supply voltage
Current
One-way wire length
Wire gauge
Conductor material
Voltage drop
Voltage lost
Voltage at the load
Round-trip resistance
Length at a 3% drop
Frequently asked questions
How do I use the Voltage Drop Calculator?
Fill in the fields above — the result recalculates instantly as you type. Everything runs in your browser, so the values you enter are never collected or stored.
Is this calculator free?
Yes. It is completely free, requires no account, and works on phones, tablets and desktops.