Wire Gauge Calculator
Determine the correct wire gauge based on current, distance, and voltage drop requirements
Circuit Parameters
Maximum continuous current draw
Wire Run
Panel to load (not round-trip)
Additional Settings
Recommended Wire Gauge
Step-by-Step Calculation
How Wire Gauge Is Determined
Choosing the right wire gauge involves two separate checks: ampacity (can the wire safely carry the current without overheating?) and voltage drop (will too much voltage be lost over the wire length?). The required wire gauge is the larger of the two results.
Voltage Drop Formula (Single Phase):
Vdrop = (2 × L × I × R) ÷ 1000
Where L = one-way distance (ft), I = current (amps), R = resistance (ohms per 1,000 ft)
Voltage Drop % = (Vdrop ÷ Source Voltage) × 100
NEC Ampacity Table (NEC 310.16)
| AWG | Diameter (in) | Copper Ampacity | Aluminum Ampacity | Common Use | ||
|---|---|---|---|---|---|---|
| 60°C | 75°C | 60°C | 75°C | |||
| 14 | 0.064" | 15A | 15A | — | — | 15A lighting circuits |
| 12 | 0.081" | 20A | 20A | 15A | 15A | 20A outlets (most common) |
| 10 | 0.102" | 30A | 30A | 25A | 25A | 30A dryer, water heater, AC |
| 8 | 0.128" | 40A | 50A | 30A | 40A | 40-50A range, EV charger |
| 6 | 0.162" | 55A | 65A | 40A | 50A | 50-60A sub-panels, large AC |
| 4 | 0.204" | 70A | 85A | 55A | 65A | 70-85A feeders |
| 3 | 0.229" | 85A | 100A | 65A | 75A | 100A sub-panel feeders |
| 2 | 0.258" | 95A | 115A | 75A | 90A | 100-115A feeders |
| 1 | 0.289" | 110A | 130A | 85A | 100A | Large feeders |
| 1/0 | 0.325" | 125A | 150A | 100A | 120A | 150A service entrance |
| 2/0 | 0.365" | 145A | 175A | 115A | 135A | 200A feeders (copper) |
| 3/0 | 0.410" | 165A | 200A | 130A | 155A | 200A service (copper) |
| 4/0 | 0.460" | 195A | 230A | 150A | 180A | 200A service (aluminum) |
Based on NEC Table 310.16 for not more than 3 current-carrying conductors in raceway/cable at 30°C ambient temperature.
Copper vs. Aluminum Wire
Copper
- • Better conductivity (lower resistance)
- • Smaller wire size for same ampacity
- • More durable and corrosion-resistant
- • Required for most branch circuits
- • More expensive per foot
- • Standard for 14-10 AWG residential
Aluminum
- • 61% the conductivity of copper
- • Needs larger gauge for same ampacity
- • Much lighter and less expensive
- • Common for service entrance (SE) cable
- • Requires anti-oxidant compound
- • Must use AL-rated connectors and breakers
Wire Sizing Tips
- Always size wire for the breaker, not just the load — a 20A breaker requires #12 AWG minimum
- For continuous loads (running 3+ hours), multiply the current by 1.25 before sizing
- Voltage drop becomes the controlling factor for long runs, even at low amperage
- Low-voltage circuits (12V, 24V) need much heavier wire than 120V for the same wattage
- Always check local codes — they may be stricter than the NEC minimum
- Derate ampacity when more than 3 conductors are in a conduit or ambient temperature exceeds 30°C
- Use stranded wire for conduit runs (easier to pull) and solid wire for NM-B (Romex) residential
- Ground wire can be one size smaller than the circuit conductors per NEC 250.122
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Important: This calculator provides guidance based on NEC standards. Actual wire sizing must account for ambient temperature, conduit fill, conductor bundling, and local code amendments. All electrical work should be performed by a licensed electrician and inspected per local requirements.
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