Wire Gauge Calculator
Enter the circuit current and one-way wire run length to find the minimum safe AWG wire gauge. Results follow NEC ampacity tables with 3% and 5% voltage drop limits.
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Min. AWG gauge
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Ampacity of that wire
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Actual voltage drop
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Voltage drop %
AWG Wire Size Chart (Copper, 60°C/140°F rating)
| AWG | Diameter | Ampacity (NEC 60°C) | Typical use |
|---|---|---|---|
| 14 AWG | 1.63 mm | 15 A | 15 A branch circuits, lighting |
| 12 AWG | 2.05 mm | 20 A | 20 A branch circuits, kitchens, bathrooms |
| 10 AWG | 2.59 mm | 30 A | Dryers, water heaters, EV charging (30 A) |
| 8 AWG | 3.26 mm | 40 A | Ranges, large AC units |
| 6 AWG | 4.11 mm | 55 A | Sub-panels, hot tubs |
| 4 AWG | 5.19 mm | 70 A | Sub-panels, large HVAC |
| 2 AWG | 6.54 mm | 95 A | Service entrance, large sub-panels |
| 1/0 AWG | 8.25 mm | 125 A | Service entrance |
| 2/0 AWG | 9.27 mm | 145 A | Service entrance |
Note: Lower AWG numbers = thicker wire = higher ampacity. Aluminum wire requires two gauges larger than copper for the same ampacity.
Understanding Voltage Drop
Voltage drop is the reduction in voltage as current travels through a wire. Long runs of undersized wire cause significant voltage drop, which leads to:
- Dimmer lights and slower motors
- Overheating of wire and equipment
- Equipment malfunction or failure
The NEC recommends no more than 3% voltage drop on a branch circuit and 5% total from the service panel to the final load.
Voltage Drop Formula
For a two-wire (single-phase) circuit:
$$V_{drop} = \frac{2 \times K \times I \times L}{CM}$$
Where K = 12.9 (copper) or 21.2 (aluminum) for resistivity, I = current in amps, L = one-way length in feet, and CM = wire cross-section in circular mils.
Frequently Asked Questions
What wire gauge do I need for a 20 amp circuit?
A standard 20 A 120 V branch circuit requires 12 AWG copper wire minimum (NEC 310.15). Never use 14 AWG on a 20 A breaker — it is rated for 15 A only.
What wire do I need for a 240 V dryer?
A standard electric dryer draws 30 A at 240 V and requires 10 AWG copper wire (or 8 AWG aluminum). The circuit uses a 4-wire configuration: two hot legs, one neutral, and one ground.
Can I use aluminum wire in my home?
Aluminum wiring is used for service entrance conductors and large-gauge branch circuits (8 AWG and larger) and is acceptable when properly terminated with AL-rated connectors. Avoid aluminum for 15 A and 20 A branch circuits due to expansion/contraction issues and connection reliability concerns.
