Wire Size Calculator
How to Calculate Wire Size
Two Key Factors
When determining wire size, two requirements must be met:
- Ampacity: The wire must handle the current without overheating (NEC Table 310.16)
- Voltage Drop: The wire must deliver voltage within acceptable limits (typically 3% for branch circuits)
Ampacity Calculation
Minimum Ampacity = Load Current × 125% (for continuous loads)
Select wire size from NEC Table 310.16 that meets or exceeds this value.
Voltage Drop Calculation
Maximum Allowable Voltage Drop = System Voltage × (Max Drop % / 100)
For single phase: Wire Size based on Vd = (2 × L × I × R) / 1000
Common Wire Sizes and Ampacities
Copper conductors at 75°C:
- 14 AWG: 20A
- 12 AWG: 25A
- 10 AWG: 35A
- 8 AWG: 50A
- 6 AWG: 65A
- 4 AWG: 85A
- 2 AWG: 115A
- 1/0 AWG: 150A
- 4/0 AWG: 230A
About Wire Size Calculator
Wire Size Calculator - Calculate Wire Gauge Instantly
Calculate the correct wire size for your electrical project instantly. Determine the minimum wire gauge needed based on current, distance, voltage drop, and conductor material.
How to Calculate Wire Size
When determining wire size, two requirements must be met:
- Ampacity: The wire must handle the current without overheating
- Voltage Drop: The wire must deliver voltage within acceptable limits
Step 1: Calculate Minimum Ampacity
Minimum Ampacity = Load Current × 125% (for continuous loads)
For continuous loads (operating 3+ hours), NEC requires 125% of full load current.
Step 2: Check Voltage Drop
Maximum Voltage Drop = System Voltage × (Max Drop % / 100)
For branch circuits, maximum voltage drop is typically 3%.
Common Wire Sizes and Uses
| Wire Size | Ampacity (Cu) | Ampacity (Al) | Typical Use |
|---|---|---|---|
| 14 AWG | 15A | - | Light circuits, receptacles |
| 12 AWG | 20A | 15A | General purpose, small appliances |
| 10 AWG | 30A | 25A | Dryers, A/C units, water heaters |
| 8 AWG | 40A | 35A | Electric ranges, large A/C |
| 6 AWG | 55A | 45A | Sub-panels, EV chargers |
| 4 AWG | 70A | 60A | Service entrances, feeders |
| 2 AWG | 95A | 80A | Service entrances, large feeders |
| 1/0 AWG | 125A | 105A | 150A service, feeders |
| 4/0 AWG | 195A | 165A | 200A service |
Copper vs Aluminum Wire
Copper:
- Higher conductivity (lower resistance)
- Smaller wire size for same ampacity
- More durable and flexible
- More expensive
- Standard for most applications
Aluminum:
- Lower conductivity (higher resistance)
- Larger wire size required
- Requires anti-oxide compound
- Less expensive
- Common for service entrances and large feeders
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