bolt

Voltage Drop Calculator | Estimate Voltage Drop and Percentage

Q: How do I calculate voltage drop?

Enter the required values into the input fields and press the calculate button. The tool applies the formula Vdrop = 2 x L x I x R / 1000 (single phase); % drop = Vdrop / Vsource x 100 and returns the result with a short explanation of each step, so you can check the working yourself.

Q: What is an acceptable voltage drop?

The Voltage Drop Calculator is free, private, and accurate: it runs entirely in your browser (no uploads, no accounts), applies the standard calculation, and explains each step so you can verify the result. Estimates the voltage drop along a wire run for electrical installations. Enter the conductor size, current in amps, wire length, and circuit voltage, and the tool calculates the voltage drop in volts and as a percentage, using standard conductor resistance There is no limit on usage, and it works on any device.

Q: How do I reduce voltage drop?

The three levers are wire size, distance, and current. Increase the wire gauge (larger cross-section lowers resistance), shorten the run, or reduce the load. The formula shows resistance grows with length and shrinks with cross-sectional area, so upsizing the wire one or two gauges is usually the most practical fix for long runs.

Q: Why multiply length by two?

Because current must travel out AND back — the circuit length is the full loop, so the one-way distance is doubled in the voltage-drop calculation. A 100-foot run from the panel to the outlet is 200 feet of conductor. This doubling is why voltage drop becomes significant on long runs, especially at low voltages.

Q: Does aluminum wire drop more voltage than copper?

Yes — aluminum has about 61% of copper's conductivity, so for the same gauge, length, and current, aluminum wire drops about 64% more voltage (resistance is roughly 1.64×). To match copper's performance, aluminum needs to be upsized by about two gauge numbers. The calculator uses material-specific resistivity for both.

Q: What does the Voltage Drop Calculator do?

Estimates the voltage drop along a wire run for electrical installations. Enter the conductor size, current in amps, wire length, and circuit voltage, and the tool calculates the voltage drop in volts and as a percentage, using standard conductor resistance. The calculator takes your inputs, applies the standard calculation, and returns a clear result so you can make an informed decision without doing the math by hand.

Q: What formula does the Voltage Drop Calculator use?

The Voltage Drop Calculator applies the standard formula: Vdrop = 2 x L x I x R / 1000 (single phase); % drop = Vdrop / Vsource x 100. The tool walks through each step of the calculation so you can verify the numbers yourself.

Q: Is the Voltage Drop Calculator free and private?

Yes — the Voltage Drop Calculator. There is no sign-up, no paywall, no trial, and no limit on how many calculations you can run. CalcaTools covers its costs with non-intrusive display advertising, so the calculator itself never asks for payment or restricts any feature.

Q: How accurate is the Voltage Drop Calculator?

The Voltage Drop Calculator applies the standard formula: Vdrop = 2 x L x I x R / 1000 (single phase); % drop = Vdrop / Vsource x 100. It is tested against published worked examples before launch and uses native double-precision arithmetic, so results are accurate to typical precision for the values you enter — with no intermediate rounding that could distort the answer.

Calculate voltage drop along a wire run from length, gauge, current and material — copper or aluminium — with the round-trip distance applied. Size wires correctly for safe, code-compliant electrical installations.

Last updated: June 2026 · Free · No sign-up required

Results

Enter values above and click Calculate to see your result instantly.

Quick reference

Copper resistance by wire size (approx, ohms/1000 ft):

AWG	Ohms/1000 ft
14	2.525
12	1.588
10	0.999
8	0.628
6	0.395

apps Small jobs, done in one click

Everyday calculators are the workshop drawer of the site — quick utilities for the moments when you need a number now and a phone calculator won't cut it. Age, date difference, GPA, fuel cost, time-to-decimal, password strength — pick a tool and you're one click from your answer.

speed Loads in under a second

Every tool is plain HTML + JavaScript with the calculation logic compiled in. No spinner, no "verifying browser" splash, no five-second wait while ads load. Hit the page, fill the form, get the answer. Slow tools waste your time and ours.

devices Works on every device

Responsive design tested down to a 320px-wide phone screen. The input fields use native number/date keyboards on iOS and Android, the calculate button is thumb-sized, and the result still reads big and bold on the smallest screen. No app to download, ever.

sentiment_satisfied No funny business

No newsletter pop-ups, no "create an account to see the answer", no fake countdown, no fake stock counter, no upsell. Two ad slots per page (clearly labelled as Advertisement) keep the site free — that's the whole business model.

Interpretation guide

Acceptable voltage drop:

Guideline	Limit
Branch circuit	<= 3% recommended
Feeder + branch	<= 5% total
Effect of long runs	More drop, may need larger wire
Effect of higher current	Proportionally more drop

lightbulb Worked example

Let's say you are using the Voltage Drop Calculator. Estimates the voltage drop along a wire run for electrical installations. Enter the conductor size, current in amps, wire length, and circuit voltage, and the tool calculates the voltage drop in Enter the values that match your situation into the input fields and press calculate — using realistic numbers makes the result directly useful for you.

Result: The calculator instantly applies the formula Vdrop = 2 x L x I x R / 1000 (single phase); % drop = Vdrop / Vsource x 100 and returns the result with appropriate precision.

What this means: Read the result in the context of what you are measuring. The step-by-step breakdown lets you confirm the math and understand which input most affects the outcome.

Formula & methodology

Formula: Vdrop = 2 x L x I x R / 1000 (single phase); % drop = Vdrop / Vsource x 100

The Voltage Drop Calculator is built on a well-established calculation method. It uses the formula Vdrop = 2 x L x I x R / 1000 (single phase); % drop = Vdrop / Vsource x 100 to turn your inputs into a reliable result. Estimates the voltage drop along a wire run for electrical installations. Enter the conductor size, current in amps, wire length, and circuit voltage, and the tool calculates the voltage drop in volts and as a The steps are shown on the page so you can follow the reasoning from input to output.

Voltage drop is the loss along a conductor due to its resistance. The calculator multiplies the one-way distance by two (out and back for single phase), the current, and the wire's resistance per length to get the volts lost, then expresses it as a percentage of source voltage. Long runs and high current increase drop; upsizing the conductor (lower AWG number) reduces it. Codes typically recommend keeping drop at or below 3% on branch circuits.

Authoritative source: timeanddate.com

Frequently asked questions

How do I calculate voltage drop?

Enter the required values into the input fields and press the calculate button. The tool applies the formula Vdrop = 2 x L x I x R / 1000 (single phase); % drop = Vdrop / Vsource x 100 and returns the result with a short explanation of each step, so you can check the working yourself.

What is an acceptable voltage drop?

The Voltage Drop Calculator is free, private, and accurate: it runs entirely in your browser (no uploads, no accounts), applies the standard calculation, and explains each step so you can verify the result. Estimates the voltage drop along a wire run for electrical installations. Enter the conductor size, current in amps, wire length, and circuit voltage, and the tool calculates the voltage drop in volts and as a percentage, using standard conductor resistance There is no limit on usage, and it works on any device.

How do I reduce voltage drop?

The three levers are wire size, distance, and current. Increase the wire gauge (larger cross-section lowers resistance), shorten the run, or reduce the load. The formula shows resistance grows with length and shrinks with cross-sectional area, so upsizing the wire one or two gauges is usually the most practical fix for long runs.

Why multiply length by two?

Because current must travel out AND back — the circuit length is the full loop, so the one-way distance is doubled in the voltage-drop calculation. A 100-foot run from the panel to the outlet is 200 feet of conductor. This doubling is why voltage drop becomes significant on long runs, especially at low voltages.

Does aluminum wire drop more voltage than copper?

Yes — aluminum has about 61% of copper's conductivity, so for the same gauge, length, and current, aluminum wire drops about 64% more voltage (resistance is roughly 1.64×). To match copper's performance, aluminum needs to be upsized by about two gauge numbers. The calculator uses material-specific resistivity for both.

What does the Voltage Drop Calculator do?

Estimates the voltage drop along a wire run for electrical installations. Enter the conductor size, current in amps, wire length, and circuit voltage, and the tool calculates the voltage drop in volts and as a percentage, using standard conductor resistance. The calculator takes your inputs, applies the standard calculation, and returns a clear result so you can make an informed decision without doing the math by hand.

What formula does the Voltage Drop Calculator use?

The Voltage Drop Calculator applies the standard formula: Vdrop = 2 x L x I x R / 1000 (single phase); % drop = Vdrop / Vsource x 100. The tool walks through each step of the calculation so you can verify the numbers yourself.

Is the Voltage Drop Calculator free and private?

Yes — the Voltage Drop Calculator. There is no sign-up, no paywall, no trial, and no limit on how many calculations you can run. CalcaTools covers its costs with non-intrusive display advertising, so the calculator itself never asks for payment or restricts any feature.

How accurate is the Voltage Drop Calculator?

The Voltage Drop Calculator applies the standard formula: Vdrop = 2 x L x I x R / 1000 (single phase); % drop = Vdrop / Vsource x 100. It is tested against published worked examples before launch and uses native double-precision arithmetic, so results are accurate to typical precision for the values you enter — with no intermediate rounding that could distort the answer.

Explore the full everyday toolkit

Every CalcaTools everyday calculator — dates, time, age, measurements, home projects, and lifestyle tools — ready when you need a quick answer.