Wire Gauge Calculator

Calculate AWG diameter, copper wire resistance, voltage drop, and power loss for a two-conductor circuit.

AWG wire performance

Enter the American Wire Gauge and circuit operating values. Length is the one-way run; the calculation includes the return conductor.

Units

Wire Gauge (AWG)

One-way Wire Length (ft)

Current (A)

System Voltage (V)

About wire gauge calculations

American Wire Gauge (AWG) is a logarithmic standard that describes the diameter of round, solid, nonferrous electrical conductors. A smaller gauge number represents a larger conductor. This calculator converts an AWG number to diameter with the standard relationship d = 0.127 × 92^((36 − AWG)/39), where d is measured in millimetres. It then derives circular cross-sectional area from πd²/4. These geometric values are useful when comparing wire sizes or checking whether a conductor fits a terminal. Electrical resistance depends on conductor resistivity, total current-path length, and cross-sectional area. This calculator assumes copper at approximately 20°C and uses a resistivity of 1.724 × 10⁻⁸ ohm-metres. Because a typical circuit has an outgoing and returning conductor, the entered one-way distance is doubled. The displayed resistance therefore represents the complete circuit path rather than one isolated wire. Real resistance rises as copper heats, so measurements in hot conduit, attics, engine compartments, or tightly bundled cable can be higher. Voltage drop is current multiplied by round-trip resistance. The percentage compares that drop with system voltage, while power loss is current squared multiplied by resistance. These values help reveal why a cable that can safely carry a load may still perform poorly over a long distance. Excessive drop can cause dim lighting, weak motor starting, nuisance shutdowns, and wasted energy. Designers often target no more than about three percent drop on a branch circuit, but applicable electrical codes and equipment instructions always take priority. Use the result as an engineering estimate, not as approval for an installation. Ampacity also depends on insulation temperature rating, conductor material, ambient temperature, bundling, termination ratings, installation method, and local code. Stranded conductors and aluminum conductors differ from the copper model used here. Select the final wire size using the governing electrical code and have critical work reviewed by a qualified electrician.

Wire gauge examples

Inputs	Calculated output	Application
12 AWG, 50 ft, 20 A, 120 V	3.31 mm²; 3.18 V drop	Typical copper branch-circuit estimate
10 AWG, 100 ft, 30 A, 240 V	5.26 mm²; 5.99 V drop	Longer 240 V feeder estimate
18 AWG, 25 ft, 2 A, 12 V	0.823 mm²; 1.28 V drop	Shows why low-voltage runs need careful sizing

How to use the calculator

Enter the numeric AWG size printed on the copper wire.
Measure and enter the one-way distance from source to load.
Enter the expected operating current and system voltage.
Select Calculate Wire Performance and compare the drop percentage with your design limit.

Frequently asked questions

Does a lower AWG number mean a larger wire?

Yes. AWG is an inverse scale, so 10 AWG has a larger diameter and area than 12 AWG. The larger conductor normally has lower resistance per unit length.

Why does the calculator double the wire length?

Current must travel from the source to the load and return to the source. Doubling the one-way run models that complete loop for a two-conductor circuit.

What copper temperature does this estimate assume?

The resistance model uses copper resistivity near 20°C. Operating temperature, connections, and conductor construction can increase actual resistance.

Is voltage drop the same as ampacity?

No. Ampacity concerns safe current carrying capacity, while voltage drop concerns circuit performance. A design must satisfy both requirements.

Can I use this result for aluminum wire?

Not directly, because aluminum has a higher resistivity than copper. Use an aluminum-specific calculation and the applicable code tables.