Wire Size Calculator - NEC

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. Supports continuous and non-continuous loads, copper and aluminum conductors, 6 insulation types, and both conduit and free air installations. Works 100% offline on the job site.

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 daily
• Electrical apprentices studying for journeyman exams
• Electrical engineers and designers
• Electrical contractors bidding jobs
• NEC code exam preparation
• Journeyman and master electrician exam study

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