Wire Length Calculator
Calculate total wire needed for a project including box connections and waste factor, with cost estimate.
Results
Visualization
How It Works
Accurately estimating wire length prevents costly shortages and excessive waste. Always add extra for box connections (where wire is stripped and terminated) and a waste factor for cuts, mistakes, and routing changes.
The Formula
Total = Base + Box Extra + Waste
Base = Runs × Avg Length
Box Extra = Runs × Extra Per Box × 2
Waste = Base × Waste% / 100
Base = Runs × Avg Length
Box Extra = Runs × Extra Per Box × 2
Waste = Base × Waste% / 100
Variables
- Runs — Number of individual wire runs in the project
- Avg Length — Average distance of each wire run in feet
- Extra Per Box — Additional wire at each end for stripping and connections (typically 6-12 inches)
- Waste % — Percentage added for cutting errors, routing changes, and unusable remnants
Example
3 runs at 50 ft each, 1 ft extra per box, 10% waste: Base = 150 ft. Box extra = 3 x 1 x 2 = 6 ft. Waste = 150 x 0.10 = 15 ft. Total = 171 ft. At $0.25/ft = $42.75.
Tips
- Buy wire by the spool (250 ft or 500 ft) for better pricing on larger projects.
- NEC requires a minimum of 6 inches of free conductor at each box opening.
- Add 15-20% waste factor for projects with many turns, offsets, or difficult routing.
- Service entrance and feeder wire is more expensive so estimate carefully.
- Keep leftover wire organized by gauge for future repairs and additions.