Wire Size Calculator
Calculate proper AWG wire size based on amperage, distance, and voltage. NEC-compliant with voltage drop calculations and copper vs aluminum comparison.
NEC recommends maximum 3% voltage drop for branch circuits and 5% total (feeder + branch).
Copper Wire
6 AWG
Circuit Analysis
| Copper | Aluminum | |
|---|---|---|
| Required Size | 6 AWG | 4 AWG |
| Ampacity | 55A | 55A |
| Cost | Higher | ~40% less |
| Connections | Standard | Special lugs required |
Common AWG Reference (Copper, 75°C)
| AWG | Ampacity | Typical Use |
|---|---|---|
| 14 | 15A | Lighting circuits |
| 12 | 20A | General outlets |
| 10 | 30A | Dryers, water heaters |
| 8 | 40A | Ranges, large AC |
| 6 | 55A | Subpanels |
| 4 | 70A | Large feeders |
- Always verify with local codes - requirements vary by jurisdiction
- Ampacity values assume 75°C rated wire in proper conduit
- Apply derating factors for bundled wires or high ambient temperature
- Motor circuits require 125% of full load amps
- Aluminum requires anti-oxidant compound and proper torque
Related Calculators
About This Calculator
Selecting the correct wire size is critical for electrical safety and efficiency. Undersized wire creates fire hazards from overheating, while oversized wire wastes money on unnecessary material costs. Our Wire Size Calculator determines the proper AWG (American Wire Gauge) for your circuit based on amperage, distance, and voltage, while ensuring compliance with NEC (National Electrical Code) requirements and voltage drop recommendations.
Whether you're wiring a subpanel, running power to an outbuilding, installing a 240V appliance circuit, or adding an EV charger, this calculator helps you select wire that's safe, code-compliant, and efficient for your specific application. With copper prices remaining elevated in 2026 ($5.50-6.00/lb on COMEX), proper wire sizing saves money by avoiding oversizing while ensuring safety by never undersizing.
Understanding wire sizing involves two separate requirements that must both be met: ampacity (the wire's current-carrying capacity based on NEC tables) and voltage drop (the loss of voltage over distance). For short runs, ampacity usually determines wire size. For long runs to outbuildings, detached garages, or subpanels, voltage drop often requires larger wire than ampacity alone would dictate.
Trusted Sources
How to Use the Wire Size Calculator
- 1Select your circuit type (120V, 240V single-phase, or 3-phase).
- 2Enter the maximum load current in amperes from the circuit breaker or equipment nameplate.
- 3Enter the one-way distance from the panel to the load (not round-trip).
- 4In advanced mode, adjust the maximum voltage drop percentage (3% recommended).
- 5Compare copper vs. aluminum options for cost-effectiveness on your specific run.
- 6Review the recommended wire size and verify it meets both ampacity AND voltage drop requirements.
- 7For motor circuits, multiply nameplate amps by 125% per NEC 430.22.
2026 Electrical Wire Prices
Copper prices remain elevated in 2026 due to continued demand from EV infrastructure, renewable energy projects, and data centers. Current pricing from major suppliers:
THHN/THWN-2 Copper Wire Prices (2026):
| AWG | Ampacity (75°C) | Price/Foot | 100ft Cost | 500ft Cost |
|---|---|---|---|---|
| 14 | 15A | $0.18-0.25 | $18-25 | $85-115 |
| 12 | 20A | $0.24-0.32 | $24-32 | $110-150 |
| 10 | 30A | $0.38-0.48 | $38-48 | $175-225 |
| 8 | 40A | $0.58-0.75 | $58-75 | $275-350 |
| 6 | 55A | $0.85-1.10 | $85-110 | $400-525 |
| 4 | 70A | $1.25-1.60 | $125-160 | $600-775 |
| 3 | 85A | $1.55-2.00 | $155-200 | $750-975 |
| 2 | 95A | $1.95-2.50 | $195-250 | $950-1,200 |
| 1 | 110A | $2.45-3.10 | $245-310 | $1,200-1,500 |
Aluminum Wire Prices (40-50% less than copper):
| AWG | Ampacity (75°C) | Price/Foot | Equivalent Copper |
|---|---|---|---|
| 6 | 40A | $0.45-0.55 | 8 AWG Cu |
| 4 | 55A | $0.55-0.70 | 6 AWG Cu |
| 2 | 75A | $0.75-0.95 | 4 AWG Cu |
| 1/0 | 100A | $1.05-1.35 | 2 AWG Cu |
| 2/0 | 115A | $1.35-1.70 | 1 AWG Cu |
| 3/0 | 130A | $1.65-2.10 | 1/0 AWG Cu |
| 4/0 | 150A | $2.00-2.55 | 2/0 AWG Cu |
Prices vary by region and supplier. Bulk purchases (1,000ft+) typically 15-25% lower per foot.
NEC Wire Sizing Requirements
The National Electrical Code establishes minimum wire sizes for safety. Understanding these requirements prevents inspection failures and fire hazards:
NEC 240.4(D) - Maximum Overcurrent Protection:
| Wire Size | Maximum Breaker | Typical Use |
|---|---|---|
| 14 AWG Cu | 15A max | Lighting circuits only |
| 12 AWG Cu | 20A max | General outlets, small appliances |
| 10 AWG Cu | 30A max | Dryers, water heaters, small A/C |
| 8 AWG Cu | 40A max | Ranges, large A/C units |
| 6 AWG Cu | 55A max | Large subpanels, EV chargers |
NEC Circuit-Specific Requirements:
| Circuit Type | NEC Section | Minimum Wire | Notes |
|---|---|---|---|
| Kitchen small appliance | 210.11(C)(1) | 12 AWG | Two 20A circuits required |
| Bathroom | 210.11(C)(3) | 12 AWG | Dedicated 20A circuit |
| Laundry | 210.11(C)(2) | 12 AWG | 20A circuit required |
| Garage | 210.11(C)(4) | 12 AWG | 20A for vehicle charging |
| HVAC equipment | 440.35 | Per nameplate | 125% of rated amps |
| Electric dryer | 220.54 | 10 AWG | 30A typical |
| Electric range | 220.55 | 8-6 AWG | 40-50A typical |
2026 Code Updates:
- NEC 2023/2026 requires 200A minimum for new single-family homes (210.64)
- EV ready circuits now required in new construction (NEC 220.57)
- AFCI/GFCI requirements expanded to more locations
NEC Voltage Drop Guidelines
The National Electrical Code recommends (not requires) limiting voltage drop to prevent equipment problems:
NEC Recommendations (Informational Notes):
- Branch circuits: Maximum 3% voltage drop
- Feeder circuits: Maximum 3% voltage drop
- Total (feeder + branch): Maximum 5% voltage drop
Why Voltage Drop Matters:
| Voltage Drop | Effect on Equipment |
|---|---|
| 0-3% | Ideal - full power, optimal efficiency |
| 3-5% | Acceptable - minor efficiency loss, slight dimming |
| 5-7% | Problems starting motors, visible light dimming |
| 7-10% | Motor overheating, shortened equipment life |
| 10%+ | Equipment damage, potential fire risk |
Example - 3% Drop on Different Voltages:
| Voltage | 3% Drop | Voltage at Load |
|---|---|---|
| 120V | 3.6V | 116.4V |
| 240V | 7.2V | 232.8V |
| 208V (3-phase) | 6.2V | 201.8V |
When to Limit to 2% or Less:
- Sensitive electronics (computers, servers, medical equipment)
- Variable frequency drives (VFDs)
- LED lighting systems on long runs
- Motor starting circuits with high inrush
- Audio/video production equipment
AWG Wire Size Reference Chart
Complete American Wire Gauge reference with maximum distances at 3% voltage drop:
Copper Wire - 75°C Rating (Most Common):
| AWG | Ampacity | Diameter (in) | Max Distance @ 3% Drop |
|---|---|---|---|
| 120V/20A | |||
| 14 | 15A | 0.064 | 50 ft |
| 12 | 20A | 0.081 | 65 ft |
| 10 | 30A | 0.102 | 85 ft |
| 8 | 40A | 0.128 | 55 ft |
| 6 | 55A | 0.162 | 70 ft |
| 4 | 70A | 0.204 | 55 ft |
| 3 | 85A | 0.229 | 65 ft |
| 2 | 95A | 0.258 | 75 ft |
| 1 | 110A | 0.289 | 90 ft |
| 1/0 | 125A | 0.325 | 110 ft |
| 2/0 | 145A | 0.365 | 140 ft |
| 3/0 | 165A | 0.410 | 175 ft |
| 4/0 | 195A | 0.460 | 220 ft |
Key Insight: 240V circuits can run twice as far as 120V circuits for the same percentage voltage drop because current is halved for the same wattage.
Copper vs. Aluminum Wire Comparison
Each conductor material has trade-offs that affect cost, installation, and long-term reliability:
Copper Wire Advantages:
- Better conductivity (1.68 μΩ·cm vs 2.82 μΩ·cm for aluminum)
- Smaller wire size for same ampacity (2 AWG sizes smaller)
- Easier to work with (more flexible, easier terminations)
- Standard connections work on all devices
- Better corrosion resistance in most environments
- Higher scrap value at end of life
Aluminum Wire Advantages:
- 40-50% less expensive than equivalent copper
- 70% lighter weight (easier to pull through conduit)
- Abundant domestic supply (less price volatility)
- Standard for utility service entrance cables
- Excellent for long feeder runs and subpanels
When to Use Each Material:
| Application | Recommended Material | Reason |
|---|---|---|
| Branch circuits (15-20A) | Copper | Easier terminations, flexibility |
| Kitchen/bathroom outlets | Copper | Code-standard connections |
| Service entrance (100-400A) | Aluminum | Cost savings, industry standard |
| Subpanel feeders (60-200A) | Either | Aluminum for cost, copper for ease |
| Long runs (100+ ft) | Aluminum | Significant cost savings |
| Wet/corrosive locations | Copper | Better corrosion resistance |
| EV charger circuits | Copper | Per manufacturer specs |
| Motor circuits | Copper | Better performance with VFDs |
Cost Comparison Example - 100A Subpanel, 100ft Run:
| Option | Wire Size | Material Cost | Installation |
|---|---|---|---|
| Copper | 3 AWG | $600-800 | Easier |
| Aluminum | 1/0 AWG | $320-430 | Requires anti-ox |
Aluminum savings: $280-370 (35-45%) on materials alone.
Voltage Drop Calculation Formulas
Understanding the math behind wire sizing helps verify calculator results and handle special cases:
Single-Phase Voltage Drop Formula:
VD = (2 × K × I × D) / CM
Where:
VD = Voltage drop (volts)
K = Resistivity constant (12.9 for copper, 21.2 for aluminum)
I = Current (amperes)
D = One-way distance (feet)
CM = Circular mils (wire cross-sectional area)
Three-Phase Voltage Drop:
VD = (1.732 × K × I × D) / CM
Percentage Voltage Drop:
VD% = (VD / Source Voltage) × 100
Circular Mils by AWG:
| AWG | Circular Mils | AWG | Circular Mils |
|---|---|---|---|
| 14 | 4,110 | 2 | 66,360 |
| 12 | 6,530 | 1 | 83,690 |
| 10 | 10,380 | 1/0 | 105,600 |
| 8 | 16,510 | 2/0 | 133,100 |
| 6 | 26,240 | 3/0 | 167,800 |
| 4 | 41,740 | 4/0 | 211,600 |
| 3 | 52,620 | 250 MCM | 250,000 |
Example Calculation: 30A load, 100 feet one-way, 120V, copper 10 AWG:
- 10 AWG = 10,380 circular mils
- VD = (2 × 12.9 × 30 × 100) / 10,380
- VD = 77,400 / 10,380 = 7.46 volts
- VD% = (7.46 / 120) × 100 = 6.2% - exceeds 3%
Upgrading to 6 AWG (26,240 CM):
- VD = 77,400 / 26,240 = 2.95 volts = 2.5% - acceptable
NEC Ampacity Derating Requirements
NEC requires reducing wire ampacity in certain conditions. Failure to derate properly is a common inspection failure:
Standard Conditions (NEC Table 310.16):
- Ambient temperature: 30°C (86°F)
- No more than 3 current-carrying conductors
- Properly sized raceway or cable
Temperature Derating (NEC Table 310.15(B)(1)):
| Ambient Temp | 60°C Wire | 75°C Wire | 90°C Wire |
|---|---|---|---|
| 31-35°C (87-95°F) | 0.91 | 0.94 | 0.96 |
| 36-40°C (96-104°F) | 0.82 | 0.88 | 0.91 |
| 41-45°C (105-113°F) | 0.71 | 0.82 | 0.87 |
| 46-50°C (114-122°F) | 0.58 | 0.75 | 0.82 |
| 51-55°C (123-131°F) | 0.41 | 0.67 | 0.76 |
Conduit Fill Derating (NEC Table 310.15(C)(1)):
| Current-Carrying Conductors | Derating Factor |
|---|---|
| 1-3 | 1.00 (no derating) |
| 4-6 | 0.80 |
| 7-9 | 0.70 |
| 10-20 | 0.50 |
| 21-30 | 0.45 |
| 31-40 | 0.40 |
Derating Calculation Example: 10 AWG THHN copper in attic (45°C) with 6 current-carrying conductors:
- Base ampacity: 35A (90°C column for calculation)
- Temperature factor: 0.87 (for 41-45°C)
- Conduit fill factor: 0.80 (for 4-6 conductors)
- Derated ampacity: 35A × 0.87 × 0.80 = 24.4A
This wire can only safely carry 24A despite being "30A wire."
Common Wire Sizing Applications
Quick reference for typical residential and light commercial circuits:
Residential Branch Circuits:
| Circuit | Breaker | Minimum Wire | Typical Run |
|---|---|---|---|
| General lighting | 15A | 14 AWG Cu | Up to 50 ft |
| General outlets | 20A | 12 AWG Cu | Up to 65 ft |
| Kitchen countertop | 20A | 12 AWG Cu | 2 circuits required |
| Bathroom | 20A | 12 AWG Cu | Dedicated circuit |
| Laundry | 20A | 12 AWG Cu | Dedicated circuit |
| Garage | 20A | 12 AWG Cu | Per NEC 210.11(C)(4) |
| Outdoor outlets | 20A | 12 AWG Cu | GFCI protected |
| Garbage disposal | 20A | 12 AWG Cu | Usually shared with dishwasher |
| Dishwasher | 20A | 12 AWG Cu | Can share with disposal |
| Microwave (built-in) | 20A | 12 AWG Cu | Dedicated circuit |
| Refrigerator | 20A | 12 AWG Cu | Dedicated recommended |
240V Appliance Circuits:
| Appliance | Breaker | Minimum Wire | Notes |
|---|---|---|---|
| Electric dryer | 30A | 10 AWG Cu | 4-wire required |
| Electric range | 40-50A | 8-6 AWG Cu | Based on rating |
| Electric oven | 30-40A | 10-8 AWG Cu | Verify nameplate |
| Cooktop | 30-40A | 10-8 AWG Cu | Separate from oven |
| Water heater | 30A | 10 AWG Cu | 4500W typical |
| Central A/C | 20-40A | 12-8 AWG Cu | Per nameplate MCA |
| Heat pump | 30-60A | 10-6 AWG Cu | Per nameplate MCA |
| Hot tub | 40-60A | 8-6 AWG Cu | GFCI required |
| Pool pump | 20A | 12 AWG Cu | GFCI required |
| EV charger (L2) | 40-60A | 8-4 AWG Cu | 80% continuous rule |
Subpanel Feeders (Copper):
| Subpanel | Minimum Wire | Max Distance @ 3% |
|---|---|---|
| 60A | 6 AWG | 75 ft |
| 100A | 3 AWG | 60 ft |
| 125A | 2 AWG | 55 ft |
| 150A | 1/0 AWG | 85 ft |
| 200A | 2/0 AWG | 90 ft |
Pro Tips
- 💡Always use the 75°C ampacity column when wire connects to standard terminals, breakers, or outlets - the 90°C rating is only for derating calculations in hot environments.
- 💡For aluminum connections, apply anti-oxidant compound (Noalox, Penetrox) and torque lugs to manufacturer specifications - improper torque causes most aluminum connection failures.
- 💡Size wire for both ampacity AND voltage drop requirements, then use the larger of the two sizes. Short runs are usually ampacity-limited; long runs are usually voltage drop-limited.
- 💡Motor circuits require 125% sizing per NEC 430.22 - a 16A motor needs wire rated for 20A minimum, plus additional sizing for voltage drop on long runs.
- 💡When in doubt, go one wire size larger - the cost difference between 10 AWG and 8 AWG is typically $50-80 per 100 feet but provides significant safety margin and reduced voltage drop.
- 💡For subpanels in detached buildings, always run 4 wires: 2 hots, neutral, and a separate ground conductor. NEC 250.32(B) prohibits using the neutral as ground in detached structures.
- 💡Buy wire in 250ft or 500ft spools when possible - per-foot pricing at big box stores is typically 30-50% higher than spool pricing for the same wire.
- 💡EV chargers are continuous loads - multiply the charger amperage by 1.25 to determine minimum circuit and wire size (a 40A charger needs 50A wiring).
- 💡Consider future expansion when sizing feeder circuits - upgrading from 100A to 200A later costs significantly more than running larger wire initially.
- 💡Verify conduit fill before pulling wire - NEC Chapter 9 Table 1 limits fill to 40% for 3+ conductors. Oversized conduit makes pulling easier and allows for future additions.
- 💡For underground runs, use direct burial cable (UF-B) or individual THWN conductors in Schedule 40 PVC conduit. Burial depth requirements vary by installation type (NEC 300.5).
- 💡Keep wire runs as short as possible by locating panels strategically - every foot of wire adds cost, voltage drop, and installation labor.
Frequently Asked Questions
For a 30A circuit, NEC requires minimum 10 AWG copper or 8 AWG aluminum. However, for runs longer than 50-60 feet at 240V (or 25-30 feet at 120V), you may need to upsize to 8 AWG copper or 6 AWG aluminum to keep voltage drop under 3%. Always calculate both ampacity and voltage drop, then use the larger wire size required.
