15 A over 75 ft
- Percent drop
- 2.9775%
- Load voltage
- 116.427 V
- Wire resistance
- 1.588 ohms / 1000 ft
This is a simplified estimate. Use local electrical code, conductor temperature, material, raceway, and a licensed electrician for real installations.
Voltage Drop Calculator
Use this free voltage drop calculator to estimate voltage drop, percent drop, and load voltage for simple copper wire runs.
Research-backed assumptions Formula steps Examples included Private in-browser use
Formula steps
- Look up the approximate copper conductor resistance for the selected AWG size.
- Double the one-way length for the out-and-back circuit path.
- Divide the voltage drop by source voltage to show the percent drop.
How to use the voltage drop calculator
- Enter source voltage, current, one-way run length, copper AWG size, and phase type.
- Press Calculate voltage drop to see volts dropped, percent drop, and estimated load voltage.
- Use this as a simplified planning estimate only.
- Check local electrical code and a qualified professional before real electrical work.
Common uses
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.
Examples
Voltage drop estimate
Percent drop estimate
Load voltage estimate
Frequently asked questions
Plain-language answers about when to use the tool, what it does with your inputs, what to double-check, and how privacy works.
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.
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.