Wire Size NEC 310 Calculator

ZkDev

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About this app

NEC wire size calculator for electricians, apprentices, and electrical engineers. Determine the correct wire gauge (AWG/kcmil) for any circuit using official NEC ampacity tables and derating factors. This electrician app and electrical wire sizing calculator supports continuous and non-continuous loads, copper and aluminum conductors, 6 insulation types, and both conduit and free air installations. Works 100% offline on any job site — no subscription required.

Whether you're sizing wire for a 200A feeder, checking ampacity for a motor circuit, or verifying derating factors for a conduit full of wires, this wire size calculator gives you accurate NEC-compliant results in seconds. Use it as your wire gauge calculator and AWG chart reference from breaker to wire size matching with ampacity table lookup built in.

WIRE SIZE CALCULATOR FEATURES:
• Continuous and non-continuous load sizing (125% factor per NEC)
• 5 voltage presets: 120V, 208V, 240V, 277V, 480V
• Single-phase and three-phase support
• Copper and aluminum conductors: 14 AWG through 2000 kcmil
• 6 insulation types: THHN, THW, TW, XHHW-2, NM-B, USE-2
• Conduit and free air installation methods
• Temperature correction factor (NEC 310.15(B)(1))
• Conduit fill adjustment factor (NEC 310.15(C)(1))
• Termination rating check (60°C / 75°C per NEC 110.14(C))
• Overcurrent protection sizing (NEC 240.4(D))
• Optional voltage drop check when distance is provided
• PASS/FAIL indicator for quick compliance check

NEC AMPACITY TABLE REFERENCES:
• NEC Table 310.16 - Ampacity in conduit/raceway (wire size chart)
• NEC Table 310.17 - Ampacity in free air
• NEC Table 310.15(B)(1) - Temperature correction factors
• NEC Table 310.15(C)(1) - Conduit fill adjustment factors
• NEC 110.14(C) - Termination temperature limits
• NEC 240.4(D) - Small conductor overcurrent protection

PRO FEATURES (one-time purchase):
• No ads - clean interface for professionals
• Save wire size calculation history
• Export calculations as PDF reports for permits and records
• Dark theme support

HOW THE WIRE SIZE CALCULATOR WORKS:
1. Enter load current in amps
2. Select load type (continuous or non-continuous)
3. Choose voltage, phase, conductor material, insulation type
4. Set installation method and ambient temperature
5. Get recommended wire size with full derating breakdown

The wire size calculator automatically applies:
• 125% continuous load factor
• Temperature correction for ambient conditions
• Conduit fill adjustment for conductor count
• Termination temperature limit verification
• Standard breaker size selection per NEC 240.4(D)

BUILT FOR ELECTRICIANS ON THE JOB SITE:
This wire size calculator is designed by electricians, for electricians. Enter your circuit parameters, get the recommended wire size instantly - no complicated menus or unnecessary features. One-hand operation, instant results.

PERFECT FOR:
• Licensed electricians sizing wire on daily service calls
• Electrical apprentices studying for journeyman and master exams
• Electrical engineers and system designers
• Electrical contractors bidding commercial and residential jobs
• NEC code exam preparation and electrical trade certification
• Journeyman and master electrician exam study and practice

OFFLINE & PRIVACY:
• Works 100% offline - no internet needed on the job site
• No account required
• No data collection - your wire size calculations stay on your device

Simplify your wire sizing on the job site.

What’s new

• Cross-promotion: discover our other NEC calculator apps
• In-app review for easier rating
• Firebase Analytics for better app experience
• Dynamic version display in settings
• Bug fixes and performance improvements