How to Calculate Wire Gauge
What is Wire Gauge?
Wire Gauge Calculator helps contractors and tradespeople accurately size, spec, and estimate materials and systems.
Formula
Min Wire Size = Load Amperage / 0.8 (NEC 80% rule) → look up AWG table
Step-by-Step Guide
- 1Calculate load in amps, apply 80% derating, look up NEC wire gauge table
- 2Apply the formula using your project measurements
- 3Add required safety factors or waste allowances per code
Worked Examples
Input
20A circuit, 80% rule
Result
Min = 20/0.8 = 25A capacity → use 10 AWG
Common Mistakes to Avoid
- ✕Not applying code-required safety factors or derating
- ✕Forgetting to account for waste and cut losses in material estimates
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