Wire Gauge Calculator
Size a conductor against both limits that matter — carrying the current and holding the voltage — and find out which one is actually driving the answer.
Circuit
The current the circuit actually draws. This calculator does not add the 125% continuous-load factor — apply it yourself if the load runs for three hours or more.
Distance from the panel to the load. The return path is already accounted for.
Ordinary 120 V and 240 V branch circuits. A percentage limit is much tighter in absolute volts at low voltage — 3% of 120 V is 3.6 V, but 3% of 12 V is only 0.36 V, which is why low-voltage DC runs often need heavy wire long before ampacity becomes the issue.
Conductor
Aluminum has roughly 60% the conductivity of copper, so it generally needs one to two sizes larger for the same job.
The higher column only helps if every terminal and device in the circuit is rated for that temperature too.
3% on a branch circuit is the usual target, with 5% across the feeder and branch circuit combined. These are recommendations in the NEC, not requirements.
Recommended Size
copper, 75°C (167°F) insulation
Voltage drop governs. A smaller conductor would carry the current, but over this run length it would drop more voltage than you allowed.
Read before you wire anything
This is an estimate for planning, not a code-compliant design, and it does not guarantee compliance with any code. A real installation also has to account for ambient temperature correction, conduit fill and bundling derates, the 125% continuous-load factor, the temperature rating of the terminals at both ends (which often forces you back to the 75°C column even with 90°C wire), the overcurrent device you are protecting the conductor with, and local amendments to the code. None of that is applied here.
Use the result to plan and budget, then have the work designed and inspected to your local electrical code and carried out by a licensed electrician. Getting conductor sizing wrong causes overheating and fires.
AWG Reference
Ampacity shown for copper at 75°C (167°F), from NEC Table 310.16 at 30°C ambient in a raceway, capped by the small-conductor rule where it applies. Resistance is DC resistance at 75°C.
| Size | Circular mils | mm² | Diameter (in) | Ω / 1000 ft | Ampacity (A) |
|---|---|---|---|---|---|
| 14 AWG | 4,110 | 2.08 | 0.0641 | 3.07 | 15 |
| 12 AWG | 6,530 | 3.31 | 0.0808 | 1.93 | 20 |
| 10 AWG | 10,380 | 5.26 | 0.1019 | 1.21 | 30 |
| 8 AWGrecommended | 16,510 | 8.37 | 0.1285 | 0.764 | 50 |
| 6 AWG | 26,240 | 13.3 | 0.1620 | 0.491 | 65 |
| 4 AWG | 41,740 | 21.2 | 0.2043 | 0.308 | 85 |
| 3 AWG | 52,620 | 26.7 | 0.2294 | 0.245 | 100 |
| 2 AWG | 66,360 | 33.6 | 0.2576 | 0.194 | 115 |
| 1 AWG | 83,690 | 42.4 | 0.2893 | 0.154 | 130 |
| 1/0 AWG | 105,600 | 53.5 | 0.3249 | 0.122 | 150 |
| 2/0 AWG | 133,100 | 67.4 | 0.3648 | 0.0967 | 175 |
| 3/0 AWG | 167,800 | 85 | 0.4096 | 0.0766 | 200 |
| 4/0 AWG | 211,600 | 107 | 0.4600 | 0.0608 | 230 |
Frequently Asked Questions
- How do I work out what wire gauge I need?
- Two things decide it. The conductor has to carry the current without overheating, which is its ampacity, and it has to deliver the voltage the equipment needs, which means keeping voltage drop over the run within a few percent. Size for each separately, then use whichever answer is larger. This calculator does both and tells you which one governed.
- Which matters more, ampacity or voltage drop?
- It depends almost entirely on distance. On a short run inside a house, ampacity is usually the limit and voltage drop is a non-issue. Past roughly 100 feet, voltage drop starts to take over, and on a long run out to a shed, well or barn it is nearly always what forces a larger conductor than the current alone would suggest.
- What is an acceptable voltage drop?
- The usual targets are 3 percent on a branch circuit and 5 percent for the feeder and branch circuit combined. In the NEC these appear as informational notes rather than requirements, so they are good practice rather than a hard rule, but equipment that runs low on voltage draws more current, runs hotter and lasts less time.
- Why does aluminum need a bigger wire than copper?
- Aluminum conducts about 61 percent as well as copper, so for the same size it has higher resistance, a lower ampacity and more voltage drop. In practice an aluminum conductor is typically one to two AWG sizes larger than the copper equivalent. Aluminum also needs terminals listed for it and an antioxidant compound at the connections.
- Does the 60, 75 or 90°C column change the wire size?
- It can, but the higher columns are often unusable. The whole circuit is limited by the lowest temperature rating in it, and most breakers and devices are rated 60 or 75°C, so 90°C wire is usually sized from the 75°C column. The 90°C figures are mainly there as a starting point for derating when conductors are bundled or run somewhere hot.
- Is this result code compliant?
- No. It is a planning estimate. A real installation also has to account for ambient temperature correction, conduit fill and bundling derates, the 125 percent factor for continuous loads, terminal temperature ratings, the overcurrent device protecting the conductor and any local amendments — none of which are applied here. Have the work designed and inspected to your local code and done by a licensed electrician.
- Does this work for DC circuits?
- Yes. The resistive voltage drop calculation is identical for DC and single-phase AC: current travels out along one conductor and back along the other, so the same factor of two applies. Select DC as the current type. The resistance figures used here are DC resistance, so nothing is approximated for a DC run, whereas AC results ignore the small reactive component.
- What wire size do I need for a 12 volt DC run?
- Set the current type to DC and the system voltage to 12 V. Expect a larger conductor than the same current would need at 120 V, because a percentage limit is far tighter in absolute volts at low voltage: 3% of 12 V is only 0.36 V. On low-voltage DC runs voltage drop almost always decides the size long before ampacity does.
- Do these figures apply to automotive, marine or solar wiring?
- Only as a rough guide. The ampacity and resistance data here follow the National Electrical Code, which governs premises wiring in buildings. Automotive, marine and RV work follow different standards such as SAE and ABYC E-11, which use their own ampacity tables, temperature assumptions and drop targets, and often allow smaller conductors for short engine-bay runs. Use the standard that applies to your installation.