Wire Gauge Calculator

Find the right wire size for any electrical circuit - current capacity, resistance, and voltage drop.

Wire Gauge (AWG)

Material

Wire Gauge (AWG)

Current (A)

One-Way Run Length (m)

System Voltage (V)

Material

📖 What is a Wire Gauge Calculator?

A wire gauge calculator helps electricians, engineers, and DIY enthusiasts select the correct wire size for any electrical circuit. Choosing the right wire gauge is critical for safety and efficiency - undersized wire overheats and is a fire risk, while oversized wire wastes money without adding benefit.

In the US and many other countries, wire size is measured in AWG (American Wire Gauge). The AWG system works inversely - a smaller number means a thicker wire. AWG 10 is thicker than AWG 14. For very large conductors, the kcmil (thousand circular mils) system is used instead.

This calculator provides two modes. The AWG Lookup mode gives you the diameter, cross-sectional area, resistance per metre, and maximum current capacity (ampacity) for any gauge of copper or aluminium wire. The Voltage Drop mode calculates how much voltage is lost along a given run of wire - essential for long cable runs in homes, solar installations, and industrial settings.

Wire ampacity depends on the insulation type, installation method (in conduit, buried, open air), ambient temperature, and bundling with other conductors. The values shown here are for single-conductor copper wire at 30°C ambient - always verify with NEC Table 310.16 or your local wiring regulations for final design.

📝 Wire Gauge Formulas

AWG Diameter:
d = 0.005 × 92^((36 − AWG) / 39) inches

Cross-Sectional Area:
A = π × (d/2)² mm²

Resistance per metre (copper):
R/m = ρ / A where ρ(Cu) = 1.724 × 10⁻⁸ Ω·m, ρ(Al) = 2.82 × 10⁻⁸ Ω·m

Total Resistance (round trip):
R_total = R/m × 2 × L

Voltage Drop:
V_drop = I × R_total

Voltage Drop Percentage:
V_drop% = (V_drop / V_source) × 100

Where: d = diameter | A = area (m²) | ρ = resistivity | L = one-way length (m) | I = current (A)

✍️ How to Use This Calculator

AWG Lookup mode: Select a wire gauge from the dropdown and choose copper or aluminium. Click Calculate to see diameter, area, resistance, and ampacity.
Voltage Drop mode: Switch to the Voltage Drop tab, enter the wire gauge, current load, one-way run length, and system voltage.
Click Calculate to see total resistance, voltage drop in volts, and voltage drop percentage.
If voltage drop exceeds 3%, go up one or two AWG sizes (lower number) and recalculate.
For critical runs, keep total drop (feeder + branch) below 5% per NEC recommendations.

📄 Example Calculations

Example 1 - Selecting wire for a 20 A kitchen circuit:
A 20 A circuit needs wire with ampacity ≥ 25 A (125% rule for continuous loads).
AWG 12 copper has ampacity of 20 A (in conduit, 75°C). AWG 10 copper has ampacity of 30 A.
Result: Use AWG 10 copper for a 20 A continuous load (or AWG 12 if truly non-continuous).

Example 2 - Voltage drop for a 30 m run:
Circuit: 15 A load, AWG 12 copper, 30 m one-way run, 230 V system.
R/m (AWG 12 Cu) ≈ 0.00529 Ω/m
R_total = 0.00529 × 2 × 30 = 0.318 Ω
V_drop = 15 × 0.318 = 4.76 V
V_drop% = 4.76 / 230 × 100 = 2.07% ✓ (under 3%) Try this example →

Frequently Asked Questions

What is AWG and how does it work?+

AWG stands for American Wire Gauge - the standard US system for measuring wire diameter. Counterintuitively, a lower AWG number means a thicker wire. AWG 4 is thicker than AWG 12. Each decrease of 3 AWG roughly doubles the cross-sectional area. AWG 0 (1/0), 00 (2/0), 000 (3/0), and 0000 (4/0) are used for very heavy-duty applications.

What happens if I use wire that is too thin?+

Undersized wire overheats when carrying its rated load. This wastes energy, degrades insulation, and is a serious fire hazard. Always use wire rated for at least 125% of the continuous load. Circuit breakers protect wiring - they must be sized to trip before the wire is damaged.

What is voltage drop and why does it matter?+

Voltage drop is the reduction in voltage along the length of a wire due to its resistance. High voltage drop means appliances receive less voltage than designed for, causing motors to overheat, lights to dim, and sensitive electronics to malfunction. NEC recommends keeping branch circuit voltage drop below 3%.

How do I calculate voltage drop?+

Voltage drop = Current (A) × Wire Resistance (Ω). Wire resistance = Resistivity × Length / Cross-sectional Area. For copper: resistivity ≈ 1.724 × 10⁻⁸ Ω·m. This calculator handles the maths - enter your current, wire gauge, and one-way run length.

Should I use copper or aluminium wire?+

Copper is preferred for most residential wiring - it has lower resistivity, is easier to work with, and is more reliable at connections. Aluminium is used for large service entrance conductors and feeders where the lower cost and weight matter. Always use proper aluminium-rated connectors and anti-oxidant compound with aluminium wire.

How do I choose the right wire gauge for a circuit?+

Select wire gauge based on maximum continuous current and acceptable voltage drop. Key AWG ratings (copper, 60C): 14 AWG = 15A, 12 AWG = 20A, 10 AWG = 30A, 8 AWG = 40A, 6 AWG = 55A. The higher the AWG number, the thinner the wire. For long runs, check that voltage drop is under 3% for power circuits and under 1% for sensitive loads. Thicker wire (lower AWG number) is always better for safety - never undersize a wire.

What happens if wire gauge is too small?+

Undersized wire has higher resistance, causing: (1) Excessive voltage drop - devices receive less voltage than designed for. (2) Heat generation - resistance causes I^2R heating, which can melt insulation and cause fires. (3) Breaker nuisance tripping - voltage drop causes motors to draw more current, tripping circuit protection. Always use wire rated for at least 125% of the expected continuous load current. For high-resistance runs (solar systems, EV charging), upsize by one or two AWG sizes to minimise losses.

What happens if I use wire that is too thin for the current?+

Undersized wire has higher resistance, which causes excessive voltage drop and heat generation. The heat (P = I^2 x R) can melt insulation, create fire hazards, and trip circuit breakers. National electrical codes specify minimum wire gauges for each circuit current rating precisely to prevent this. For motor loads, wire must also handle inrush current at startup (typically 6-8x running current). Always use the wire gauge specified by your local electrical code or a licensed electrician - oversizing wire is safe, undersizing is dangerous.

How do I select wire gauge for a long DC run?+

For long DC runs, voltage drop is the critical factor, not just current capacity. Calculate voltage drop = I x R x 2L (round trip). For a 10 A load at 12 V over 10 m using 2.5 mm squared wire (R = 7.41 mohm/m): drop = 10 x 0.00741 x 20 = 1.48 V (12.3%). Use this calculator's voltage drop mode and target less than or equal to 3% drop for lighting, less than 5% for motors.