What Is the Voltage Drop for 8 AWG at 13A and 25 Feet?

8 AWG at 13A and 25 feet: 0.5057V drop (0.4214% on 120V), computed on the single-phase / DC basis. Every conductor has resistance, and longer runs at higher currents drop more voltage. Use this calculation to check whether your run clears the 3% branch-circuit drop target before pulling wire.

8 AWG, 13A, 25ft · single-phase / DC

0.5057 V drop (0.4214% on 120V)

On 120V circuit0.4214%

On 240V circuit0.2107%

Circuit basis: This uses the single-phase / DC round-trip formula (factor of 2) for the voltage drop across the two circuit conductors. For a three-phase line-to-line run use the three-phase version of the page (append ?type=3ph). Switch to the three-phase version →

Gauge

8 AWG

Amps

Feet

Drop @ 120V

0.51V (0.42%)

Assumes a 120V source on a single-phase / DC circuit. Use the circuit-basis link above to switch between single-phase/DC and three-phase.

Voltage Drop Formula (single-phase / DC)

V_drop = (2 × L × I × R) ÷ 1000

(2 × 25 × 13 × 0.778) ÷ 1000 = 0.5057 V

DC and single-phase AC use the round-trip factor of 2. Current travels out to the load on one conductor and returns on another.

For a three-phase circuit at the same amps and distance, see the three-phase version (uses √3 instead of 2, so the drop is about 13.4% lower).

Percentage

%VD = (V_drop ÷ V_source) × 100

On 120V: (0.5057 ÷ 120) × 100 = 0.4214%

On 240V: (0.5057 ÷ 240) × 100 = 0.2107%

How This Estimate Changes with Run Length and Gauge

Gauge Check

8 AWG clears the 3% drop target at these inputs. A smaller conductor may also meet it with less margin. See the minimum gauge for this load and distance.

Impact of Distance

Voltage drop is proportional to distance. Here is 8 AWG at 13A at different distances:

Distance	Drop (V)	% on 120V	% on 240V	NEC (120V)
25ft	0.5057V	0.4214%	0.2107%	OK
50ft	1.01V	0.8428%	0.4214%	OK
75ft	1.52V	1.26%	0.6321%	OK
100ft	2.02V	1.69%	0.8428%	OK
150ft	3.03V	2.53%	1.26%	OK
200ft	4.05V	3.37%	1.69%	Caution
300ft	6.07V	5.06%	2.53%	Past 5%

Same Run, Different Wire Gauges

How does wire gauge affect voltage drop for 13A at 25 feet on 120V single-phase / DC? Only gauges whose branch-circuit OCP cap is at or above the 13A load are listed, since thinner gauges would fail the ampacity check before drop even matters.

Gauge	Drop (V)	% on 120V	% on 240V	3% Target (120V)
8 AWG	0.5057V	0.4214%	0.2107%	OK
6 AWG	0.3192V	0.266%	0.133%	OK
4 AWG	0.2002V	0.1668%	0.0834%	OK
3 AWG	0.1593V	0.1327%	0.0664%	OK
2 AWG	0.1261V	0.1051%	0.0525%	OK
1 AWG	0.1001V	0.0834%	0.0417%	OK

Related Calculations

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Frequently Asked Questions

What is the voltage drop for 8 AWG at 13A and 25ft?expand_more

8 AWG carrying 13A over 25ft has a 0.5057V drop (0.4214% on 120V). Reference: 0.2107% on 240V.

Why does distance affect voltage drop?expand_more

Voltage drop is proportional to distance. The formula multiplies by 2 × the distance (out and back). Doubling the run doubles the drop.

What wire gauge should I use instead of 8 AWG for this run?expand_more

8 AWG already sits within the 3% branch-circuit drop target at these inputs (0.4214% on 120V). Going to a larger gauge is only useful if you want more headroom for future load growth, longer runs, or tighter drop targets like the 5% feeder+branch total recommendation used in sensitive or motor-heavy installations.

Is voltage drop worse on 120V or 240V?expand_more

Same wire, same amps, same distance: the volts dropped are identical. But the percentage is worse on 120V because the drop is a larger fraction of the source voltage. This run would be 0.2107% on 240V versus 0.4214% on 120V.

Does 8 AWG meet the 3% drop target at 13A and 25ft on 120V?expand_more

On 120V, this run sits at 0.4214%, which is within the 3% branch and 5% feeder+branch total drop targets. NEC 210.19(A) Informational Note 4 cites 3% for branch circuits and 5% for total feeder+branch drop as performance recommendations, not hard code requirements.

This calculator provides estimates for reference purposes only. Always consult a licensed electrician and verify compliance with the National Electrical Code (NEC) and local electrical codes before performing any electrical work.