Wire Size Calculator — Complete Guide to AWG Wire Gauge Selection
Choosing the correct wire size is one of the most important decisions in any electrical installation. An undersized wire can overheat, cause fires, or fail to deliver enough power to your devices. Our free wire size calculator helps you determine the exact AWG (American Wire Gauge) or metric wire size you need based on your current load, wire length, voltage, and acceptable voltage drop.
What is AWG (American Wire Gauge)?
AWG stands for American Wire Gauge — a standardized wire gauge system used predominantly in North America. The AWG number works inversely: a lower AWG number means a thicker (larger) wire with higher current capacity. For example, AWG 4 is much thicker than AWG 22.
- AWG 0000 (4/0): Very thick — used for main electrical panels, 260A capacity
- AWG 12: Standard household wiring — 30A capacity
- AWG 14: Light household circuits — 25A capacity
- AWG 18-22: Low-voltage applications, electronics, signal wires
How to Use the Wire Size Calculator
- Enter your current load in amperes (A) — this is the maximum current your circuit will carry
- Enter wire length — the one-way distance from power source to load
- Enter system voltage — typically 120V (US), 230V (Europe), or 12V/24V (DC)
- Select max voltage drop — NEC recommends max 3% for branch circuits, 5% total
- Choose conductor material — copper has lower resistance than aluminum
Voltage Drop Formula
The wire size is calculated using the voltage drop formula:
Required Area (mm²) = (2 × Length × Current × Resistivity) ÷ Max Voltage Drop (V)
Where resistivity = 0.0172 Ω·mm²/m for copper, 0.0282 Ω·mm²/m for aluminum.
Wire Size Selection Rules
- Always size up — if calculated size is between two gauges, always choose the thicker wire
- Temperature derating — in hot environments (above 30°C), reduce wire ampacity by 10-20%
- Conduit fill — multiple wires in a conduit require derating
- Copper vs Aluminum — for the same current capacity, aluminum wire needs to be about 2 AWG sizes larger than copper
Common Wire Sizes for Home Wiring
| AWG | Common Use | Max Amps |
|---|
| AWG 14 | Lighting circuits | 15A |
| AWG 12 | General outlets (20A circuits) | 20A |
| AWG 10 | Dryers, A/C units | 30A |
| AWG 8 | Electric ranges, large A/C | 40A |
| AWG 6 | Sub-panels, EV chargers | 55A |
⚠️ Safety Note: Always consult a licensed electrician for actual electrical installations. Wire sizing depends on many factors including insulation type, ambient temperature, conduit fill, and local electrical codes. This calculator is for educational and estimation purposes only.