Quick start
- Enter source voltage and current in amps.
- Enter one-way wire length in feet.
- Choose copper AWG size and phase type.
Best uses
These are the situations this tool is meant for. If your task is close to one of these, the examples and notes below can help you choose the right inputs.
- Estimate voltage drop for a branch circuit run.
- Compare common copper AWG wire sizes.
- Check percent voltage drop from source voltage.
- See load voltage after the estimated drop.
What this calculator is solving
The Voltage Drop Calculator is for early planning and learning. It estimates the voltage lost across a copper conductor run, then shows the percent drop and load voltage.
You do not need to memorize the formula first. Start by matching each input label on the calculator to the number, date, unit, or setting you actually have.
The formula in plain language
In plain language: The calculator multiplies current by conductor resistance and one-way length. Single-phase/DC uses a 2x path factor; three-phase uses the square root of 3. The examples on the page are there so you can compare your inputs with a filled-out calculation before copying the answer.
If that sounds abstract, use the example cards on the calculator page. They show a complete set of inputs and the kind of answer you should expect.
How to read the answer
Read the headline result first. Then look at the smaller supporting lines because they explain the parts behind the answer, such as totals, units, ranges, or formula steps.
- Voltage drop is the estimated volts lost in the conductor.
- Percent drop compares that loss with source voltage.
- Load voltage is the source voltage minus estimated drop.
Common mistakes to avoid
If the answer looks strange, the most likely cause is a small input mismatch: the wrong unit, date, weight, scale, mode, or policy assumption.
- Do not use this as a final wiring design.
- Do not forget that conductor material, temperature, and installation method matter.
- Ask a qualified electrician for real installations.
Research and references
These references shaped the calculator assumptions, unit choices, or safety notes.
Examples from the calculator
Voltage drop estimate
Percent drop estimate
Load voltage estimate
FAQ in plain language
When should I use the Voltage Drop Calculator?
Use it when your task matches one of these common needs: Estimate voltage drop for a branch circuit run. Compare common copper AWG wire sizes. It works best when you already know the values, dates, units, or settings the page asks for.
What is the Voltage Drop Calculator doing with my inputs?
In plain language: The calculator multiplies current by conductor resistance and one-way length. Single-phase/DC uses a 2x path factor; three-phase uses the square root of 3. The examples on the page are there so you can compare your inputs with a filled-out calculation before copying the answer.
What should I double-check before trusting the answer?
This is a simplified planning estimate. Real electrical work needs code checks, conductor temperature, material, installation method, and a qualified professional. Also check that you used the right unit, date, scale, or mode because small input changes can change the result.
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Privacy and copying results
Recent answers stay visible only while you work in the current browser tab. They are not sent to a server.
Use Copy answer when you want to paste the expression and result into notes, homework, a message, or another document. Check the units and assumptions before copying.