This calculator estimates the voltage drop of an electrical circuit based on NEC data, estimated resistance from wire size, or custom impedance values.
Modify the values and click the calculate button to use
| AWG | Diameter (in) | Diameter (mm) | Area (kcmil) | Area (mm²) | Copper Ω/km | Copper Ω/1000ft |
|---|---|---|---|---|---|---|
| 0000 (4/0) | 0.4600 | 11.684 | 212 | 107.000 | 0.1608 | 0.0490 |
| 000 (3/0) | 0.4096 | 10.404 | 168 | 85.000 | 0.2028 | 0.0618 |
| 00 (2/0) | 0.3648 | 9.266 | 133 | 67.400 | 0.2557 | 0.0779 |
| 0 (1/0) | 0.3249 | 8.252 | 106 | 53.500 | 0.3224 | 0.0983 |
| 1 | 0.2893 | 7.348 | 83.7 | 42.400 | 0.4066 | 0.1239 |
| 2 | 0.2576 | 6.544 | 66.4 | 33.600 | 0.5127 | 0.1563 |
| 3 | 0.2294 | 5.827 | 52.6 | 26.700 | 0.6465 | 0.1970 |
| 4 | 0.2043 | 5.189 | 41.7 | 21.200 | 0.8152 | 0.2485 |
| 5 | 0.1819 | 4.621 | 33.1 | 16.800 | 1.0280 | 0.3133 |
| 6 | 0.1620 | 4.115 | 26.3 | 13.300 | 1.2960 | 0.3951 |
| 7 | 0.1443 | 3.665 | 20.8 | 10.500 | 1.6340 | 0.4982 |
| 8 | 0.1285 | 3.264 | 16.5 | 8.370 | 2.0610 | 0.6282 |
| 9 | 0.1144 | 2.906 | 13.1 | 6.630 | 2.5990 | 0.7921 |
| 10 | 0.1019 | 2.588 | 10.4 | 5.260 | 3.2770 | 0.9989 |
| 11 | 0.0907 | 2.305 | 8.23 | 4.170 | 4.1320 | 1.2600 |
| 12 | 0.0808 | 2.053 | 6.53 | 3.310 | 5.2110 | 1.5880 |
| 13 | 0.0720 | 1.828 | 5.18 | 2.620 | 6.5710 | 2.0030 |
| 14 | 0.0641 | 1.628 | 4.11 | 2.080 | 8.2860 | 2.5250 |
| 15 | 0.0571 | 1.450 | 3.26 | 1.650 | 10.4500 | 3.1840 |
| 16 | 0.0508 | 1.291 | 2.58 | 1.310 | 13.1700 | 4.0160 |
| 17 | 0.0453 | 1.150 | 2.05 | 1.040 | 16.6100 | 5.0640 |
| 18 | 0.0403 | 1.024 | 1.62 | 0.823 | 20.9500 | 6.3850 |
| 19 | 0.0359 | 0.912 | 1.29 | 0.653 | 26.4200 | 8.0510 |
| 20 | 0.0320 | 0.812 | 1.02 | 0.518 | 33.3100 | 10.1500 |
| 21 | 0.0285 | 0.723 | 0.81 | 0.410 | 42.0000 | 12.8000 |
| 22 | 0.0253 | 0.644 | 0.642 | 0.326 | 52.9600 | 16.1400 |
| 23 | 0.0226 | 0.573 | 0.509 | 0.258 | 66.7900 | 20.3600 |
| 24 | 0.0201 | 0.511 | 0.404 | 0.205 | 84.2200 | 25.6700 |
| 25 | 0.0179 | 0.455 | 0.32 | 0.162 | 106.2000 | 32.3700 |
| 26 | 0.0159 | 0.405 | 0.254 | 0.129 | 133.9000 | 40.8100 |
| 27 | 0.0142 | 0.361 | 0.202 | 0.102 | 168.9000 | 51.4700 |
| 28 | 0.0126 | 0.321 | 0.16 | 0.081 | 212.9000 | 64.9000 |
| 29 | 0.0113 | 0.286 | 0.127 | 0.064 | 268.5000 | 81.8400 |
| 30 | 0.0100 | 0.255 | 0.101 | 0.051 | 338.6000 | 103.2000 |
| 31 | 0.0089 | 0.227 | 0.0797 | 0.040 | 426.9000 | 130.1000 |
| 32 | 0.0080 | 0.202 | 0.0632 | 0.032 | 538.3000 | 164.1000 |
| 33 | 0.0071 | 0.180 | 0.0501 | 0.025 | 678.8000 | 206.9000 |
| 34 | 0.0063 | 0.160 | 0.0398 | 0.020 | 856.0000 | 260.9000 |
| 35 | 0.0056 | 0.143 | 0.0315 | 0.016 | 1079.0000 | 329.0000 |
| 36 | 0.0050 | 0.127 | 0.025 | 0.013 | 1361.0000 | 414.8000 |
| 37 | 0.0044 | 0.113 | 0.0198 | 0.010 | 1716.0000 | 523.1000 |
| 38 | 0.0040 | 0.101 | 0.0157 | 0.008 | 2164.0000 | 659.6000 |
| 39 | 0.0035 | 0.090 | 0.0125 | 0.006 | 2729.0000 | 831.8000 |
| 40 | 0.0031 | 0.080 | 0.00989 | 0.005 | 3441.0000 | 1049.0000 |
Standard AWG wire sizes with copper resistance values — lower AWG = thicker wire = less resistance
Imagine you're trying to push water through a garden hose. The longer the hose, the less water pressure you get at the end. Same thing happens with electricity.
Voltage drop is simply the loss of electrical pressure as electricity travels through a wire. Every wire has some resistance. The longer the wire, the more resistance, and the more voltage you lose along the way.
Here's the thing: that lost voltage doesn't just disappear. It turns into heat. That's why wires get warm when you run electricity through them. And if the voltage drop is too big, things stop working properly.
Let's be real. Most people don't think about voltage drop until something goes wrong. Here's what happens when you ignore it:
Lights get dim — Especially noticeable with LED strips or long runs of Christmas lights
Motors run slow or overheat — Your power tools, fans, and pumps will struggle
Electronics act weird — Computers might crash, chargers might not work
Wires get hot — In extreme cases, this can start a fire
Batteries don't charge properly — Solar setups and car audio systems suffer
So yeah, it's kind of a big deal. But the good news is, it's totally preventable. You just need to use the right wire size for the job.
Our calculator does all the hard math for you. You just need to know a few things:
Wire length — How far is the electricity traveling? (Round trip, not one way)
Wire gauge — What size wire are you using? (Or what size do you want to check?)
Current — How many amps will be flowing through the wire?
Voltage — What's your system voltage? (12V, 120V, 240V, etc.)
Phase — Is it AC or DC? Single phase or three phase?
Plug those numbers in, and the calculator tells you exactly how much voltage you'll lose. It also tells you if that's acceptable or if you need a bigger wire.
Here's a mistake beginners make all the time. They measure the distance from the power source to the device. But electricity has to travel there AND back. So you need to double that distance. If your shed is 50 feet from your house, the round trip is 100 feet. Use 100 feet in the calculator.
Okay, I know formulas can be scary. But this one is actually pretty straightforward:
Voltage Drop = 2 × Length × Current × Resistance per foot
Let's break that down:
📊 Example:
10 amps through 100 feet of 12-gauge copper (resistance: 0.00162 ohms/ft). Voltage Drop = 2 × 100 × 10 × 0.00162 = 3.24 volts. On a 120V system = 2.7% drop (fine). On a 12V system = 27% drop (terrible). See why wire size matters for low-voltage?
This depends on what you're doing. Here are the general rules:
The National Electrical Code (NEC) recommends no more than 3% drop for branch circuits and 5% total from the service panel to the farthest outlet. For low-voltage systems like 12V, even a small drop is a big percentage — be extra careful.
Sarah's LED strips run 40 feet around her living room. The far end is dimmer. Problem: 18-gauge wire at 12V drops over 4 volts — a 33% loss. Fix: Use thicker wire or add a second power supply in the middle.
Mike ran 100 ft of 14-gauge cord to his shed. His circular saw (15A) barely spins. Problem: 7.6V drop = 6.3% loss. Fix: Use 10-gauge wire — drops only 3V (2.5%).
Jake's solar panels are 50 ft from the charge controller using 12-gauge wire. Problem: 1.6V drop = 6.7% loss on 24V system. Fix: Use 8-gauge wire — drops only 0.6V (2.5%).
Mistake 1: Forgetting to Double the Length
Electricity goes there AND back. Always use round-trip distance.
Mistake 2: Using the Wrong Wire Gauge
Thicker wire has less resistance. For long distances, you need thicker wire than you think.
Mistake 3: Ignoring Temperature
Hot wires have more resistance. Wires in hot attics or near heat sources will have worse voltage drop.
Mistake 4: Not Checking for DC vs AC
DC and AC voltage drop differ slightly. For long runs or high currents, it matters. Our calculator handles both.
Mistake 5: Thinking "It's Only a Few Volts"
A 3V drop on 120V = 2.5% (fine). A 3V drop on 12V = 25% (terrible). Always think in percentages.
12V DC Systems
Car audio, RVs, boats, small solar. A 1V drop = 8.3% loss. Use thick wire, keep runs short.
24V DC Systems
Better than 12V but still sensitive. Solar panels, industrial equipment. 2V drop = 8.3% loss.
120V AC Systems
Standard household US voltage. More forgiving. 3V drop = 2.5%. Still check runs over 100 feet.
240V AC Systems
Large appliances, EV chargers, workshops. Even more forgiving. 5V drop = 2.1%. Don't get complacent.
Three-Phase Systems
Industrial settings. Current distributed across three wires. Our calculator handles this automatically.
Using our calculator is dead simple. Here's the step-by-step:
Select your system type — DC, AC single-phase, or AC three-phase
Enter the voltage — Your system voltage (12, 24, 120, 240, etc.)
Enter the current — How many amps will flow
Enter the wire length — One-way distance in feet
Select wire gauge — AWG size (or enter custom wire size)
Select wire material — Copper or aluminum
Adjust temperature if needed — Default is 75°C (167°F)
Click calculate — Get your results instantly
The calculator shows you:
Skin Effect in AC Systems
At high frequencies, AC current flows mostly on the wire surface, increasing resistance. For 60Hz household power, the effect is tiny. For high-frequency applications, it matters.
Parallel Conductors
For very high currents, run multiple wires in parallel to effectively reduce resistance. Our calculator can handle this if you enter the equivalent gauge.
Voltage Drop in Conduit
Wires in conduit can't dissipate heat as well, increasing operating temperature and resistance. If your wire is in conduit, add 10-15% to your calculated drop.
It's the loss of electrical pressure as electricity travels through a wire. Like water losing pressure in a long garden hose. The longer or thinner the wire, the more voltage you lose.
Use the formula: 2 × Length × Current × Resistance per foot. Or just use our calculator — enter your wire length, gauge, current, and voltage, and it does all the math instantly.
For lights and outlets: under 3%. For motors: under 5%. For sensitive electronics: under 2%. The NEC recommends max 3% for branch circuits and 5% total from panel to farthest outlet.
Because the voltage is so low to begin with. A 3-volt drop on 120V is only 2.5% — barely noticeable. But a 3-volt drop on 12V is 25% — your lights will barely glow. Low-voltage systems need thicker wires.
Yes. Always use round-trip distance. If your shed is 50 feet from your house, electricity travels 50 feet there and 50 feet back = 100 feet total. Most beginners forget this.
Copper has about 40% less resistance than aluminum, so it has less voltage drop for the same size. Aluminum wire needs to be about 2 sizes larger to match copper's performance.
Hotter wires have more resistance. If your wire runs through a hot attic, voltage drop increases. Our calculator lets you adjust for temperature. For most indoor installations, 75°C is standard.
It depends on the current and voltage. For 15A at 120V over 100 feet, 12-gauge works (2.5% drop). For 15A at 12V over 100 feet, you'd need 4-gauge to stay under 3%. Use our calculator to be sure.
Yes, in extreme cases. Voltage drop turns into heat in the wire. If the wire is severely undersized, it can overheat and melt the insulation, potentially starting a fire. Always use properly sized wire.
For most practical purposes, they're very similar at 60Hz. At high frequencies, AC has additional effects (skin effect, inductance). For long industrial runs, the difference matters. Our calculator handles both.
Use thicker wire, keep wire runs as short as possible, use higher system voltage (24V or 48V instead of 12V), and place the charge controller close to the batteries. Every little bit helps with solar.
NEC 210.19(A) recommends branch circuit conductors be sized for no more than 3% voltage drop. NEC 215.2(A) recommends feeder conductors max 2% drop. These are recommendations, not hard requirements, but inspectors look for compliance.