How to use this calculator
- Enter Circuit amperage in A.
- Enter One-way run in ft.
- Press Calculate. The highlighted row is your order quantity; the note beneath it translates the number into real-world terms.
Formula & constants
Base gauge by breaker: 15A→14 AWG, 20A→12, 30A→10, 40A→8, 50A→6, 60A→4. Runs over ~100 ft upsize one gauge to hold voltage drop under 3%. Always verify against NEC and local code. Every default in the fields above is editable — when your supplier’s spec sheet lists a different density, coverage rate or price, enter that number instead. The waste and compaction allowances follow common trade practice; see our methodology page for the derivation of each formula and the standards it references.
Reference only — final sizing must follow NEC tables and local inspection.
Where this fits in the project
Electrical sizing works backwards from load: total demand sets service size, circuit amperage sets wire gauge, and conductor count sets conduit fill. HVAC equipment is sized from the BTU load, never from floor area alone.
How this connects to your project
No quantity stands alone — each material in the chain depends on the ones around it. These are the planning steps that pair with the wire size calculator:
- Electrical Load Calculator — Wire is sized based on circuit load in amps.
- Conduit Fill Calculator — Wires run through conduit, which has fill limits.
- Recessed Lighting Calculator — Lighting circuits use specific wire gauges.
- HVAC Size Calculator — HVAC equipment requires dedicated circuits.
- Solar Panel Calculator — Solar installations require specific wire sizing.
Frequently asked questions
What wire for a 20 amp circuit?
12 AWG copper minimum — 14 AWG on a 20 A breaker is a fire hazard and a code violation.
Why upsize wire on long runs?
Resistance drops voltage over distance; NEC recommends ≤3% drop. Past ~100 ft, one gauge thicker restores it.
Copper vs aluminum sizing?
Aluminum needs two gauge sizes larger for the same ampacity — and AL-rated terminations.
Last verified: — prices reflect current national averages. See our methodology.
Estimates are for planning. Material densities, coverage rates and prices vary by region and supplier — confirm final quantities before ordering, and check local code where structural or electrical work is involved.