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
Start here if one of these sounds like your job. The examples below show which inputs matter most.
- 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.
Match each input label on the calculator to the real measurement, amount, rate, unit, or setting for your job.
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 worked example before copying the answer.
The example cards on the calculator page show a complete set of inputs and the kind of answer you should expect.
How to read the answer
Read the main result first. Then check the smaller lines for the totals, units, ranges, counts, or formula steps behind it.
- 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: a mixed unit, copied value, wrong mode, missing label, or result used for the wrong job.
- 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 help check the measurements, units, limits, or safety notes used in this guide.
Worked examples for Voltage Drop 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 measurements, amounts, units, or options 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 worked example before copying the answer.
What do the main Voltage Drop Calculator inputs mean?
Source voltage: the voltage at the supply side before the wire run loses voltage. Current amps: the load current flowing through the conductor. One-way length: the distance from source to load. The calculator applies the circuit-path factor for the selected phase. Copper wire size: the AWG size used to look up approximate copper resistance.
How should I read the Voltage Drop Calculator answer?
Read the headline answer, then check the supporting lines and examples to understand how the calculator got there. If one input changes, rerun the tool and compare the new answer instead of guessing.
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 the unit, scale, mode, and result limit because small input changes can change the answer.
Why does circuit type change voltage drop?
A simple single-phase or DC run uses an out-and-back path, so the length factor is 2. A balanced three-phase estimate uses the square root of 3. Real installations can need more detailed impedance and code checks.
Does the site save what I enter?
No. The calculator runs in your browser tab. Your recent answers stay only on the page while you use it, and they are not sent to a server.
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Keep exploring
If this guide is close but not exact, these links keep you near the same kind of problem.
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- All calculator and utility guides Find more plain-language examples, formulas, mistakes, and result explanations.
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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 save the inputs and result in notes, homework, a message, or a project list. Check the units, labels, and limits before copying.