Wire Size Calculator
This wire size calculator finds the right conductor for a load from the current, the run length, and the allowable voltage drop. Enter those three values and the wire size calculator returns the minimum cable size in AWG and mm², so the conductor carries the current safely without overheating or losing too much voltage. It works as an electrical cable size calculator for both AC and DC circuits. It also rounds the result up to the next standard cable size and shows the nearest AWG or kcmil size.
Results
The Wire Size Calculator is part of our Cable & Protection collection. Browse more cable & protection to size, convert, and check your work alongside this tool.
What the wire size calculator does
Pick a conductor too thin and it overheats and wastes voltage; pick one too thick and you pay for copper you do not need. This wire size calculator finds the balance by sizing the cable to the current it must carry and the length of the run. As an electrical cable size calculator it checks two limits at once, the current the conductor can carry safely and the voltage drop over distance, then reports the smallest cable size that satisfies both in AWG and mm².
How the electrical cable size calculator works
Sizing a conductor comes down to two checks. The current rating check makes sure the cable can carry the load without exceeding its temperature limit. The voltage drop check makes sure the resistance over the run does not waste more than the allowed percentage:
where R is the resistance per unit length for that cable size and L is the one-way length. For three phase the factor becomes √3 instead of 2, which is why the three phase cable size calculator, the 3 phase cable size calculator, gives a smaller conductor for the same load. The wire size calculator steps up through standard sizes until both checks pass.
Wire size calculator example
A 20 A load, 30 m away, on 230 V single phase with a 3% drop limit. The electrical cable size calculator finds that a 2.5 mm² conductor drops too much over 30 m, so it steps up:
The wire size calculator returns 4 mm² (about 11 AWG) as the minimum. For a 12 V DC version of the same current, the far lower voltage forces a much larger conductor.
How to use the wire size calculator
Enter the load current in amps, the one-way run length, the system voltage, and the voltage drop you will allow, usually 3%. The wire size calculator applies the resistance of copper over that distance and returns the minimum conductor. Set the phase and the tool becomes a 3 phase cable size calculator; set a low voltage and it works as a 12 volt wire size calculator for DC circuits. It doubles as a cable selection calculator, and because it reports the conductor in AWG and mm² it answers the same question as a cable dimension calculator or cable width calculator.
Reading the wire size calculator result
The result is the minimum safe conductor, not necessarily the one to install. Round up to the next standard size for margin, and go larger still for long runs, high ambient temperature, or cables bunched in conduit, since heat derates their capacity. Low-voltage DC systems punish long runs hardest, which is why a 12 volt wire size calculator often returns surprisingly thick cable. Use the wire capacity calculator result as your floor and add headroom for future loads.
When to use the wire size calculator
- Sizing a circuit from a breaker with the electrical cable size calculator
- Checking ampacity against a breaker as a cable rating calculator
- Running long feeders with the wire gauge length calculator where the cable sizing chart alone is not enough
- Wiring solar, battery, and automotive DC with a 12 volt wire size calculator
- Balancing three-phase loads with the 3 phase cable size calculator
Common cable size calculator mistakes
- Sizing on current alone. A cable rated for the amps can still fail the voltage drop check on a long run, so the wire size calculator tests both.
- Ignoring derating. Heat and bunching lower capacity below the cable sizing chart value.
- Using half the run. Enter the one-way length; the electrical cable size calculator already accounts for the return path.
Tips for accurate results
- Enter the true one-way run length so the wire size calculator sizes for the full circuit resistance.
- Derate the cable sizing chart value for hot or bunched installations.
- Round up to the next standard size and add headroom for future loads.
Current rating versus voltage drop in the cable size calculator
The two checks behind any electrical cable size calculator answer different questions, and which one wins depends on distance. On short runs the current rating decides the cable, because the conductor simply has to carry the amps without overheating. On long runs voltage drop takes over, since resistance accumulates with length and a cable rated for the current can still deliver too little voltage at the far end. This is the single most common sizing error, and it is why a wire size calculator that only checked ampacity would undersize long feeders. Always give the real run length, not a rounded guess, since the wire size computation depends directly on it. A quick cable calculator that skips length will mislead you here.
Derating, DC, and reading a cable sizing chart
A cable sizing chart lists capacity under reference conditions, but real installations rarely match them. Cables in a hot roof space, bundled together in conduit, or buried in insulation all carry less than the chart says, so the figure from the wire size calculator is a starting point you derate for the environment. DC systems add their own twist: because 12 V and 24 V supplies have so little voltage to spare, the dc wire size calculator result is driven almost entirely by voltage drop, and doubling the run can jump the conductor two sizes. When in doubt, size up, since the cost of thicker cable is small next to the cost of rewiring.
Cable size calculation chart
Typical copper conductor sizes and their approximate current capacity, a quick cable sizing chart from the wire size calculator:
| AWG | mm² (approx) | Typical capacity (A) |
|---|---|---|
| 14 | 2.1 | 15 |
| 12 | 3.3 | 20 |
| 10 | 5.3 | 30 |
| 8 | 8.4 | 40 |
| 6 | 13.3 | 55 |
| 4 | 21.2 | 70 |
Wire Size Calculator FAQ
How does the cable size calculator choose a cable?
It finds the minimum cross section that keeps the voltage drop within your limit, then rounds up to the next standard size, such as 4 mm² for a 3.04 mm² result, and shows the nearest AWG, here 12 AWG. Always check that size against the current carrying capacity table for your installation method too.
Why is DC cable so much thicker?
At low voltage the same current is a larger share of the supply, so voltage drop dominates. A 12 volt wire size calculator often returns heavy cable because the run resistance matters far more than in a 230 V circuit.
What voltage drop should I allow?
A 3% drop for the final circuit is a common target. Enter your own limit and the wire size calculator sizes the conductor to meet it over the length you give.
Does three phase need smaller cable?
For the same power, yes. The 3 phase cable size calculator uses the √3 factor, so each conductor carries less current than the single-phase equivalent and can be a size smaller.