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 volts dropped, percent drop, and load voltage for simple copper AWG wire runs before a qualified code check.
Inputs explainedResult checksExample valuesRuns in your browser
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.
Examples
Recent answers
Recent voltage drop estimates will appear here.
This is a planning estimate only. Electrical design should be checked by a qualified professional.
Inputs and recent answers stay in this browser tab and are not sent to a server.
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.
What people use it for
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.
Explain why long, low-voltage, or high-current runs can lose more voltage.
Copy a planning result before checking equipment instructions and qualified electrical guidance.
Quick examples
120 V branch
120 V, 15 A, 75 ft, 12 AWG copper3.573 V drop, 2.98% drop, 116.427 V load
Longer 240 V run
240 V, 30 A, 100 ft, 8 AWG copper3.7692 V drop, 1.57% drop, 236.2308 V load
Three-phase run
208 V, 20 A, 150 ft, 6 AWG copper2.0533 V drop, 0.99% drop, 205.9467 V load
Low-voltage DC check
24 V, 5 A, 40 ft, 10 AWG copper0.3996 V drop, 1.67% drop, 23.6004 V load
Long thin-wire check
120 V, 12 A, 150 ft, 14 AWG copper9.09 V drop, 7.58% drop, 110.91 V load
Larger-wire comparison
120 V, 15 A, 75 ft, 10 AWG copper2.2478 V drop, 1.87% drop, 117.7523 V load
Need the guide or a nearby tool?
Need a slower walkthrough, a related calculator, or the full library? These links keep you close to the task you started.
- How to use the Voltage Drop CalculatorSee slower examples, input meanings, formula notes, result limits, and mistakes to avoid.
- CalculatorsBrowse related calculators and utilities in the same category.
- Electrical Calculator HubCompare this with the nearby tools and checks in the same job path.
- Calculator and utility guidesFind more guides that use real tool inputs and example numbers.
- All free toolsSearch every live tool, converter, calculator, AI helper, and browser utility.
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 measurements, amounts, units, or options the page asks for.
What is the Voltage Drop Calculator doing with my inputs?
In plain language: Voltage drop = current x copper resistance per foot x one-way length x circuit factor. Single-phase/DC uses factor 2; balanced three-phase uses sqrt(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 used for this estimate, not a breaker-size decision. One-way length: the source-to-load distance in feet. The calculator applies the return-path or three-phase factor. Copper wire size: the AWG size used to look up approximate copper resistance per 1,000 feet. Circuit type: single-phase/DC or balanced three-phase, which changes the circuit factor.
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?
Planning math only. It does not choose breaker or wire size and does not check ampacity, insulation, temperature, raceway fill, equipment instructions, or local code. 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 factor is 2. A balanced three-phase estimate uses sqrt(3). Real installations can need more detailed impedance and code checks.
Should I enter one-way length or round-trip length?
Enter one-way length from source to load. The calculator applies the circuit factor, so entering round-trip length would double-count the path for single-phase or DC runs.
Does this choose the correct wire size?
No. It estimates voltage drop for the wire size you pick. Wire sizing also needs ampacity, insulation, conductor material, temperature, raceway fill, terminals, equipment instructions, and local code.
Why can low-voltage runs show a high percent drop?
The same volt loss is a larger percentage of a small source voltage. A 0.4 V drop is small on 120 V, but much more noticeable on 12 V or 24 V systems.
Does this include aluminum wire or temperature adjustment?
No. This version uses approximate copper AWG resistance values. Aluminum conductors, hot conductors, conduit fill, and AC impedance can change the real 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.