Voltage drop chart: volts lost by gauge and current
This is the core voltage drop chart. Rows are wire gauge (with the metric mm² equivalent), columns are common load currents, and each cell is the volts lost over a 100 ft run — counted round trip, out and back. Because the loss scales linearly, you can read off any length: a 250 ft run loses 2.5× the figure shown, a 50 ft run half of it.
Switch the length units to metres above and the same voltage loss chart redraws as volts lost per 100 m. The drop is identical in physics either way — only the run length you are quoting changes.
Maximum wire run length chart (stay under your target)
This is the table most people are really after. For the system voltage and target you picked above, each cell is the longest one-way run that keeps a gauge under the limit at that current. It already counts the return conductor, so the distance shown is point-to-point, not doubled. Cells shaded differently are runs shorter than a metre or foot — effectively “too much current for this gauge, go bigger.”
Drop your target to a tighter percent and every maximum shortens; raise the system voltage and they all stretch out, because the same volts lost are a smaller share of a bigger number. That single relationship is why higher-voltage systems can run thinner wire much further.
12V and 24V voltage drop chart (automotive, RV, marine, solar)
Low-voltage DC gets its own section because a 12V voltage drop chart behaves very differently: 3% of 12 V is only 0.36 V, so the runs are short and surprises are common. The table below shows the maximum one-way run length at 12 V and at 24 V side by side, at your chosen target, so you can see how much slack stepping up to 24 V buys you for the same wire.
This is why van, boat and off-grid builds keep battery-to-inverter and controller-to-battery runs as short and fat as possible. For a single bespoke case — a bow thruster, a fridge run, a panel string — size it exactly in the solar wire size calculator or the voltage drop calculator.
A note on three-phase
The charts above are DC and single-phase, which is where the search demand and the head-scratching live. For a balanced three-phase line-to-line run the drop uses √3 (about 1.732) in place of the factor of 2, so a three-phase run drops roughly √3÷2 ≈ 0.87 as much as the single-phase figure for the same current and length. If you mostly work in 208/240/480 V three-phase, multiply the per-run chart by about 0.87, or enter the case directly in the calculator for an exact number.
How this voltage drop calculation table is computed
Nothing here is reproduced from a published or owned table — every cell is generated from public physics, the same way the voltage drop calculator works. Wire size comes from the AWG geometric formula; resistance is the standard reference resistivity divided by the conductor's area:
Because every figure is solved live rather than looked up in a fixed image, you can move the material, target and system voltage and watch the whole volt drop table re-solve. The source type is generic on purpose: AWG geometry from the public gauge formula, and the standard copper or aluminium reference resistivity. The tables hold 20 °C; resistance climbs a little as a conductor warms, so for a temperature-adjusted exact number on one run, use the calculator.
Voltage drop chart FAQ
How far can I run a given wire gauge?
That's what the maximum run length chart above is for: pick the system voltage and a target percentage, then read the longest one-way distance a gauge can carry a given current before the drop exceeds the target. The number is a one-way length because the chart already counts the out-and-back conductor when it works out the loss. People usually want this rather than a single computed answer, which is why it's the headline table here. For a temperature-adjusted figure for one exact case, use the voltage drop calculator.
Do I use one-way or round-trip length?
Both — and that's the step people forget. Current flows out to the load and back, so the conductor that matters is twice the one-way distance. The per-run voltage drop chart already doubles the length for you, so its cells are the full round-trip loss for the one-way distance shown. The maximum run length table reports a one-way distance for the same reason, having already accounted for the return leg. If you ever calculate it by hand, multiply your one-way run by two before you start.
Why is a 12V voltage drop chart so much stricter?
Because the percentage is measured against a small number. A 3% target on a 12V system is only 0.36 V, so a loss that would be trivial on a 120V circuit eats your whole budget on 12V. That's why a 12V voltage drop chart shows much shorter runs for the same gauge and current, and why automotive, RV, marine and solar wiring is kept short and fat. The dedicated 12V and 24V section above makes this obvious at a glance.
Does insulation or cable type change the voltage drop?
No. Voltage drop over distance depends only on the conductor's cross-sectional area, the current, and the length of the run. Insulation, jacket colour and cable type don't change the drop — they affect temperature rating and ampacity, which is a separate question this chart doesn't cover. So a thicker jacket won't reduce your voltage loss chart figures; only a larger conductor, less current or a shorter run will.
How do I scale the chart to a different length or current?
Drop is linear in both, which makes the table easy to scale. Double the current or double the length and the volts dropped double; halve either and it halves. So if the per-run chart shows a figure for 100 ft at 10 A, the same wire at 10 A over 250 ft drops 2.5 times as much, and at 20 A over 100 ft it drops twice as much. The percentage then just divides that drop by your system voltage.
What is an acceptable voltage drop — 3% or 5%?
A common rule of thumb is to keep the branch run feeding a load under about 3% and the whole path under about 5%, tightening to 1–2% on sensitive or high-current runs. These are widely used planning guidelines rather than legal limits, so adjust the target to your application — the chart lets you switch between 3%, 5% and 10% so you can see the trade-off directly. Solar installers often choose 2% to claw back wasted harvest on long runs.
Where do these voltage drop numbers come from?
Every cell is computed, not copied. Wire size comes from the public AWG geometric formula d = 0.127 × 92(36−n)/39 in millimetres, and resistance is the standard reference resistivity for copper (0.017241 Ω·mm²/m) or aluminium (0.0265 Ω·mm²/m) divided by the conductor area. Nothing here is a reproduction of any owned or copyrighted chart, and no ampacity figures are included — this is a voltage-drop and resistance reference only. The tables sit at 20 °C; resistance rises a little as the wire warms, so use the voltage drop calculator for a temperature-adjusted exact number.
Is conductor voltage drop the same as measuring drop across a fuse or connection?
No, and they're easy to confuse. This chart is about the voltage lost along the length of a healthy conductor because of its resistance. Measuring a drop across a single fuse, connector or joint is a fault-finding technique for spotting a bad connection with extra resistance — a different topic from sizing a cable run, and not what these tables are for.
Is this voltage drop chart free and printable?
Yes. It's free, needs no signup or download, and runs entirely in your browser, so you can print or screenshot it offline. The tables are real selectable HTML, not images, so they stay sharp and you can copy values straight out of the volt drop table.