Wire Size Calculator - AWG Electrical Wire Sizing
Calculate the correct wire size (AWG) for any electrical circuit based on current, voltage, and distance. NEC-compliant calculations for both copper and aluminum conductors.
Quick Reference: Common Wire Sizes
Residential Circuits:
- 15A: 14 AWG copper
- 20A: 12 AWG copper
- 30A: 10 AWG copper
- 50A: 6 AWG copper
240V Appliances:
- Dryer: 10 AWG (30A)
- Range: 8 AWG (40A)
- Hot Tub: 6 AWG (50A)
- EV Charger: 6 AWG (50A)
Service/Feeders:
- 60A Sub: 4 AWG copper
- 100A Sub: 1 AWG copper
- 200A Service: 2/0 copper
- Check voltage drop!
Important: These are starting points based on ampacity only. Always verify voltage drop for runs over 50 feet and apply derating factors for temperature, conduit fill, and continuous loads.
Wire Size Calculator
Calculate the correct AWG wire size for both copper and aluminum conductors
Input Parameters
Select a common voltage or choose 'Custom voltage' for other values
Complete Guide to Wire Sizing
How Wire Sizing Works
Wire sizing involves selecting the correct conductor size based on several factors: current carrying capacity (ampacity), voltage drop over distance, temperature conditions, and installation method. The National Electrical Code (NEC) provides tables and rules to ensure safe and efficient electrical installations.
Key Factors in Wire Sizing
- 1.Ampacity: The maximum current a conductor can carry continuously without exceeding its temperature rating.
- 2.Voltage Drop: Must not exceed 3% for branch circuits or 5% total to maintain efficiency.
- 3.Temperature Rating: Match conductor rating to lowest rated component in the circuit.
- 4.Continuous Loads: Require 125% sizing per NEC 210.19(A).
NEC Wire Sizing Rules
Table 310.16
Primary ampacity table for conductors rated 0-2000V in raceway, cable, or earth. Most residential and commercial wiring references this table.
Article 210.19
Branch circuit conductors must have ampacity not less than the maximum load served. Continuous loads require 125% conductor sizing.
Article 240.4
Small conductor rule: 14 AWG limited to 15A, 12 AWG to 20A, 10 AWG to 30A overcurrent protection regardless of calculated ampacity.
Common Circuit Wire Sizing Guide
| Circuit Type | Breaker | Wire Size | Max 120V | Max 240V | Application | Notes |
|---|---|---|---|---|---|---|
| 15A Lighting Circuit | 15A | 14 AWG | 45 ft | 90 ft | General lighting, outlets | Standard residential branch circuit |
| 20A Kitchen Circuit | 20A | 12 AWG | 60 ft | 120 ft | Kitchen countertop outlets | Required for kitchen receptacles |
| 30A Dryer Circuit | 30A | 10 AWG | N/A | 85 ft | Electric dryer | 240V circuit, 4-wire required |
| 40A Range Circuit | 40A | 8 AWG | N/A | 70 ft | Electric range/oven | May use 50A breaker |
| 50A EV Charger | 50A | 6 AWG | N/A | 75 ft | Level 2 EV charging | Continuous load consideration |
| 60A Subpanel | 60A | 4 AWG | N/A | 65 ft | Garage/workshop subpanel | 4-wire feeder required |
| 100A Subpanel | 100A | 1 AWG | N/A | 50 ft | Building subpanel | Aluminum 1/0 commonly used |
| 200A Service | 200A | 2/0 Copper | N/A | Limited | Main service entrance | 4/0 aluminum typical |
Note: Maximum distances shown maintain 3% voltage drop at rated current. Actual distances may vary based on load characteristics and installation conditions. Always verify with voltage drop calculations for critical applications.
NEC Table 310.16 - Wire Ampacity Ratings
| AWG | Copper (Amps) | Aluminum (Amps) | ||||
|---|---|---|---|---|---|---|
| 60°C | 75°C | 90°C | 60°C | 75°C | 90°C | |
| 14 | 15 | 20 | 25 | — | — | — |
| 12 | 20 | 25 | 30 | 15 | 20 | 25 |
| 10 | 30 | 35 | 40 | 25 | 30 | 35 |
| 8 | 40 | 50 | 55 | 30 | 40 | 45 |
| 6 | 55 | 65 | 75 | 40 | 50 | 55 |
| 4 | 70 | 85 | 95 | 55 | 65 | 75 |
| 3 | 85 | 100 | 115 | 65 | 75 | 85 |
| 2 | 95 | 115 | 130 | 75 | 90 | 100 |
| 1 | 110 | 130 | 145 | 85 | 100 | 115 |
| 1/0 | 125 | 150 | 170 | 100 | 120 | 135 |
| 2/0 | 145 | 175 | 195 | 115 | 135 | 150 |
| 3/0 | 165 | 200 | 225 | 130 | 155 | 175 |
| 4/0 | 195 | 230 | 260 | 150 | 180 | 205 |
Temperature Derating Required
Ampacity must be adjusted for ambient temperatures above 86°F (30°C). In attics or outdoor conduit exposed to sunlight, significant derating may be required.
75°C Column Most Common
Most circuit breakers and equipment are rated for 75°C maximum. Even with 90°C wire, you must use the 75°C ampacity at terminations.
Temperature Correction Factors
| Ambient Temperature | 60°C Wire | 75°C Wire | 90°C Wire |
|---|---|---|---|
| 70-77°F (21-25°C) | 1.00 | 1.00 | 1.00 |
| 78-86°F (26-30°C) | 0.91 | 0.94 | 0.96 |
| 87-95°F (31-35°C) | 0.82 | 0.88 | 0.91 |
| 96-104°F (36-40°C) | 0.71 | 0.82 | 0.87 |
| 105-113°F (41-45°C) | 0.58 | 0.75 | 0.82 |
| 114-122°F (46-50°C) | 0.41 | 0.67 | 0.76 |
How to Apply Temperature Correction
Multiply the table ampacity by the correction factor. Example: 12 AWG at 75°C = 25A. In 104°F ambient: 25A × 0.82 = 20.5A adjusted ampacity.
Common hot locations: Attics (140°F+), rooftops (130°F+), boiler rooms (110°F+), outdoor conduit in sun (add 20°F to ambient).
Common Wire Sizing Mistakes to Avoid
Ignoring voltage drop for long runs
Consequence: Equipment malfunction, dimming lights, motor failure
Solution: Always calculate voltage drop for runs over 50 feet
Not accounting for continuous loads
Consequence: Wire overheating, insulation damage, fire hazard
Solution: Apply 125% factor for loads running 3+ hours (NEC 210.19)
Using wrong temperature rating
Consequence: Inadequate ampacity, code violation
Solution: Match wire temperature rating to termination rating
Mixing copper and aluminum connections
Consequence: Corrosion, high resistance, connection failure
Solution: Use proper connectors rated for both materials
Undersizing neutral in multi-wire circuits
Consequence: Neutral overload with non-linear loads
Solution: Size neutral for maximum unbalanced load
Forgetting derating for bundled conductors
Consequence: Overheating when multiple wires in conduit
Solution: Apply NEC Table 310.15(C)(1) adjustment factors
Wire Cost Comparison - Copper vs Aluminum
| Wire Size | Copper $/ft | Aluminum $/ft | Typical Run | Copper Total |
|---|---|---|---|---|
| 14 AWG | $0.45 | N/A | 50 ft | $22.50 |
| 12 AWG | $0.65 | $0.35 | 50 ft | $32.50 |
| 10 AWG | $1.15 | $0.60 | 75 ft | $86.25 |
| 8 AWG | $1.95 | $1.05 | 60 ft | $117.00 |
| 6 AWG | $3.25 | $1.75 | 60 ft | $195.00 |
| 4 AWG | $5.20 | $2.80 | 80 ft | $416.00 |
| 2 AWG | $8.15 | $4.40 | 100 ft | $815.00 |
Aluminum Wire Savings
Aluminum wire typically costs 40-50% less than copper. For large feeders and services, the savings can be thousands of dollars. Requires proper AL-rated connections and installation techniques.
When to Choose Copper
Use copper for: branch circuits under 30A, tight spaces (smaller diameter), corrosive environments, high vibration areas, and where superior conductivity justifies cost.
Special Wire Sizing Considerations
Continuous Loads (3+ Hours)
NEC 210.19(A) requires conductors supplying continuous loads to be sized at 125% of the load.
Common continuous loads: EV chargers, hot tubs, commercial lighting, heating equipment
Conduit Fill Derating
More than 3 current-carrying conductors in a raceway require derating per NEC 310.15(C)(1).
Neutral and ground conductors typically don't count as current-carrying
Motor Circuits
Size at 125% of motor FLC per NEC 430.22. Starting current doesn't affect wire size but impacts voltage drop.
Parallel Conductors
Minimum 1/0 AWG for parallel runs per NEC 310.10(G). All parallel conductors must be identical in length, material, and termination.
Voltage Drop Priority
For sensitive electronics and long runs, size for 2% drop instead of 3%. Critical for LED drivers and variable frequency drives.
Professional Installation Tips
Planning Phase
- Calculate both ampacity and voltage drop
- Consider future expansion needs
- Verify temperature ratings match
- Check local code amendments
Best Practices
- Label wire runs clearly at both ends
- Use proper torque specifications
- Apply antioxidant on aluminum
- Document calculations for inspector
Common Issues
- Undersized neutrals in MWBC
- Missing derating in hot attics
- Wrong insulation type for wet areas
- Mixing wire types in same circuit
Wire Size Capacity Comparison Chart
| Wire Size | Copper 60°C | Copper 75°C | Copper 90°C | Aluminum 75°C | Common Uses |
|---|---|---|---|---|---|
| 14 AWG | 15A | 20A* | 25A | — | 15A lighting circuits |
| 12 AWG | 20A | 25A* | 30A | 20A* | 20A outlets, kitchens |
| 10 AWG | 30A | 35A* | 40A | 30A* | 30A dryers, A/C units |
| 8 AWG | 40A | 50A | 55A | 40A | 40-50A ranges, EV chargers |
| 6 AWG | 55A | 65A | 75A | 50A | 60A subpanels, hot tubs |
| 4 AWG | 70A | 85A | 95A | 65A | 100A subpanels |
| 2 AWG | 95A | 115A | 130A | 90A | 125A service feeders |
| 1/0 AWG | 125A | 150A | 170A | 120A | 150A services |
| 3/0 AWG | 165A | 200A | 225A | 155A | 200A residential services |
* Limited by NEC 240.4(D) small conductor rules. Always verify with local codes and authority having jurisdiction.
Industry Standards & Authority Resources
National Electrical Code (NEC)
- NFPA 70 - National Electrical Code
- NFPA Electrical Resources
- Article 310 - Conductors
- Table 310.16 - Ampacities
- Article 240.4(D) - Small Conductors
Professional Organizations
Professional Tip: Always consult the latest edition of the NEC and local amendments. Many jurisdictions have specific requirements that supersede national standards. When in doubt, consult with a licensed electrician or electrical inspector.
Wire Sizing Frequently Asked Questions
Q:What size wire for 20 amp circuit?
A: A 20 amp circuit requires 12 AWG copper wire or 10 AWG aluminum wire per NEC Table 310.16. This assumes 75°C rated conductors and terminations, which is standard for residential wiring.
Q:How do I calculate wire size for distance?
A: For distance calculations: 1) Start with ampacity-based size from NEC 310.16, 2) Calculate voltage drop using VD = (2 × L × I × R) ÷ 1000, 3) If drop exceeds 3%, increase wire size until within limits. Distance often requires larger wire than ampacity alone.
Q:What's the difference between THHN and ROMEX wire?
A: THHN is single conductor wire for conduit with 90°C rating (derated to 75°C at terminations). ROMEX (NM-B cable) contains multiple conductors with ground, rated 90°C but limited to 60°C ampacity per NEC 334.80. THHN has higher ampacity in conduit.
Q:Can I use aluminum wire instead of copper?
A: Yes, aluminum wire is safe when properly installed with AL-rated connections and anti-oxidant compound. Aluminum requires one size larger than copper for same ampacity (e.g., 8 AWG aluminum vs 10 AWG copper for 30A). Cost savings can be 40-50%.
Q:What size wire for 50 amp hot tub?
A: A 50 amp hot tub circuit requires 6 AWG copper or 4 AWG aluminum wire. Use 4-wire cable (two hots, neutral, ground) for 240V connection. GFCI protection required per NEC 680.42.
Q:How many amps can 12 gauge wire handle?
A: 12 AWG copper wire is rated for 25 amps at 75°C per NEC Table 310.16, but must be protected at 20 amps maximum per NEC 240.4(D). For continuous loads, derate to 80% (16 amps continuous on 20A breaker).
Q:What size wire for 100 amp subpanel 150 feet away?
A: For 100A subpanel at 150 feet, use 1/0 AWG copper or 3/0 AWG aluminum to maintain under 3% voltage drop. Ampacity alone would allow 1 AWG copper or 1/0 aluminum, but distance requires upsizing.
Q:Do I need to upsize wire for motor loads?
A: Yes, size wire at 125% of motor full-load current per NEC 430.22. For example, a 5 HP 240V motor (28A FLC) needs wire sized for 35A minimum. Also consider voltage drop during starting (6x running current).
Q:What's the maximum distance for 12 AWG wire?
A: For 12 AWG copper at 20A/120V maintaining 3% voltage drop: maximum 57 feet. At 240V: maximum 114 feet. These distances assume single-phase circuits. Reduce by 13% for three-phase.
Q:Can I run 10 gauge wire on a 30 amp breaker?
A: Yes, 10 AWG copper is rated for 35 amps at 75°C, making it suitable for 30A breakers. However, for receptacle circuits, NEC 240.4(D) limits 10 AWG to 30A overcurrent protection maximum.
Q:What size ground wire do I need?
A: Equipment grounding conductor size is based on overcurrent device per NEC Table 250.122: 15-20A circuits need 14 AWG, 30-60A need 10 AWG, 100A needs 8 AWG, 200A needs 6 AWG copper ground.
Q:How do I size wire for continuous loads?
A: For continuous loads (3+ hours), size conductors at 125% of the load per NEC 210.19(A). A 40A continuous load needs wire sized for 50A minimum. The overcurrent device must also be sized at 125%.
Q:What wire size for 200 amp service entrance?
A: 200A residential service typically uses 2/0 copper or 4/0 aluminum service entrance conductors. Many areas allow 2/0 aluminum for dwelling services per NEC 310.12. Verify local requirements.
Q:Can I use 14 gauge wire on a 20 amp circuit?
A: No, 14 AWG wire is limited to 15A circuits per NEC 240.4(D). While Table 310.16 shows 20A ampacity at 75°C, the code restricts 14 AWG to 15A overcurrent protection for safety margins.
Q:What affects wire ampacity ratings?
A: Wire ampacity is affected by: conductor material (copper vs aluminum), insulation temperature rating (60/75/90°C), ambient temperature (derating required above 86°F), number of conductors in raceway (derating for heat), and installation method.
Q:How much does wire size affect voltage drop?
A: Each AWG size increase (smaller number) roughly halves resistance. Upgrading from 12 to 10 AWG reduces voltage drop by 37%, while 10 to 8 AWG reduces it another 37%. Voltage drop is proportional to resistance.
Q:Should I oversize wire for future expansion?
A: Yes, oversizing by one AWG provides headroom for future loads and reduces voltage drop. The added cost (typically 30-40%) is often justified by energy savings and flexibility. Document spare capacity for future reference.
Q:What's the difference between stranded and solid wire?
A: Stranded wire is more flexible and resistant to fatigue, ideal for vibration or frequent movement. Solid wire is cheaper, easier to terminate, and preferred for permanent building wiring. Both have identical ampacity ratings.
Q:Can I mix wire sizes in the same circuit?
A: Yes, tap rules (NEC 240.21) allow smaller wire for short distances. The smaller wire must be protected by the larger wire's overcurrent device limitations. Common for appliance whips and fixture connections.
Q:What size wire for electric car charger?
A: EV charger wire size depends on charger rating: 32A charger needs 8 AWG (40A circuit), 40A charger needs 6 AWG (50A circuit), 48A charger needs 4 AWG (60A circuit). All require 125% sizing for continuous load.
Related Electrical Calculators
Voltage Drop Calculator
Calculate voltage loss over distance for any wire size
Ampacity Calculator
Find current carrying capacity with derating factors
Conduit Fill Calculator
Calculate conduit size for multiple conductors
Ground Wire Calculator
Size equipment grounding conductors per NEC 250.122
Circuit Breaker Calculator
Size breakers for proper overcurrent protection
Load Calculator
Calculate total electrical load for service sizing