Free Voltage Drop Calculator
Calculate voltage drop and power loss along a copper or aluminium cable run.
What is the Voltage Drop Calculator?
Calculate voltage drop and power loss along a copper or aluminium cable run.
Drop equals 2 (or 1.732 for three-phase) x resistivity x one-way length x current, divided by conductor area. It is shown in volts and as a percentage of supply, with the power lost and a check against a 3 percent guideline.
Quick, reliable engineering arithmetic saves time on site and in the workshop. These tools show their working so you can check the result.
How to use the Voltage Drop Calculator
Using the voltage drop calculator takes a minute or two. Your entries are saved in this browser, so you can come back later and carry on.
Step 1
Enter your values, choosing the units you are working in.
Step 2
Read the result and the supporting numbers shown beneath it.
Step 3
Check the result against a second method or a reference table before you rely on it.
Tips for better results
The result ignores temperature and power factor, so treat it as an estimate. Wire sizing for mains circuits must meet local electrical codes, so consult a licensed electrician.
Keep units consistent from start to finish.
These tools are for estimates. Safety critical designs need a qualified engineer.
Privacy and where your data goes
Everything you type into the voltage drop calculator stays on your own device. Zapxa does not receive your numbers or documents. If you clear your browser data, your saved entries will be removed, so download a PDF of anything you want to keep.
Frequently asked questions
What voltage drop is acceptable?
Many guidelines suggest keeping it to about 3 percent for a branch circuit, which the calculator checks. Your local code or equipment specification governs.
Why is the cable length doubled?
For DC and single-phase the current travels out and back, so the resistance of both conductors is counted. Three-phase uses a 1.732 factor.
Is the voltage drop calculator free?
Yes. It is free to use with no signup, no watermark and no usage limits.
Is my data private?
Yes. Your inputs are processed in your browser and saved only in its local storage. They are not uploaded to our servers.
Does it work on mobile?
Yes. Zapxa works on phones, tablets and desktops. Use the print button or download a PDF to keep a copy.
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