Voltage drop calculator
Estimate how much voltage a wire run loses over its length, based on wire gauge, current and material.
Fill in the fields and press Calculate to see your result here.
How this calculation works
Voltage drop is estimated as Vdrop = 2 × K × I × L ÷ 1000, where K is the resistance of the chosen wire gauge in ohms per 1,000 feet, I is the current, and L is the one-way length (the 2× accounts for the full circuit — current has to travel out and back). The result is also shown as a percentage of your system voltage; many electrical codes recommend keeping voltage drop under 3–5% for a branch circuit.
Tips
This is a planning estimate, not a substitute for code compliance
Real installations should follow your local electrical code and, for anything beyond a simple low-voltage run, a qualified electrician.
A common guideline
Voltage drop is often kept to about 3% on a single circuit. Check the rules that apply where you live.
Thicker wire drops less
A lower AWG number means a thicker wire and less drop. Doubling the length doubles the drop.
Enter one-way length
The formula already counts the return path, so enter only the distance from source to load.
Frequently asked questions
Why does aluminum show a bigger voltage drop than copper?
Aluminum has higher electrical resistance than copper for the same wire size, so it loses more voltage over the same length and current.
Is this safe to use for household wiring decisions?
Use it for general planning only. Always follow your local electrical code and consult a licensed electrician for actual installations.