Electrical Calculators

Residential service load, wire sizing, conduit fill, and circuit planning tools — built on the National Electrical Code (NEC) reference tables. Currently in development; sign up for launch notification.

Electrical work is one of the few trades where mistakes can be fatal — to people, not just materials. Undersized wire causes fires. Overloaded circuits trip breakers or, worse, fail to trip when they should. The calculators we're building for this category will reference NEC Article 220 (load calculations), Article 310 (conductor ampacity), and Article 314 (box fill) to give electricians and serious DIYers the same quick-reference math that the masonry and carpentry calculators already provide.

The first tool on the roadmap is a Residential Service Load Calculator that handles NEC Optional Method calculations for single-family dwellings — general lighting, small appliance, laundry, range, dryer, HVAC, and EV charger loads — and recommends the correct service size (100A, 200A, 320A, or 400A). After that comes a Wire Size Calculator (NEC Table 310.16 with 75°C column), a Conduit Fill Calculator (NEC Chapter 9 Table 1), and a Voltage Drop Calculator for long branch circuits and feeders.

While we build out the interactive tools, here's a quick reference for the most common electrical math residential DIYers and apprentice electricians need.

NEC Wire Ampacity Reference (75°C column, Table 310.16)

• 14 AWG copper: 20 amp rating, but limited to 15A circuits per NEC 240.4(D)
• 12 AWG copper: 25 amp rating, but limited to 20A circuits per NEC 240.4(D)
• 10 AWG copper: 35 amp rating, but limited to 30A circuits per NEC 240.4(D)
• 8 AWG copper: 50 amp rating
• 6 AWG copper: 65 amp rating
• 4 AWG copper: 85 amp rating
• 2 AWG copper: 115 amp rating
• 1/0 AWG copper: 150 amp rating
• 4/0 AWG copper: 230 amp rating (typical 200A service entrance)

Common Residential Circuit Loads

• General lighting/receptacles: 3 VA per sq ft (NEC 220.12). 2,000 sq ft home = 6,000 VA = 50A at 120V.
• Small appliance branch circuits: 1,500 VA each, minimum 2 circuits (NEC 220.52(A)).
• Laundry branch circuit: 1,500 VA (NEC 220.52(B)).
• Electric range: 8,000 VA nameplate, or NEC Table 220.55 default 8,000 VA.
• Electric dryer: 5,000 VA typical (NEC 220.54 allows 5,000 VA or nameplate).
• Electric water heater: 4,500 VA typical.
• Central AC (3-ton): ~3,500 VA compressor + ~500 VA air handler.
• EV charger (Level 2, 32A): 7,680 VA at 240V.

Voltage Drop Formula

For single-phase circuits, voltage drop is calculated as:

Where Vd = voltage drop (volts), K = 12.9 for copper (or 21.2 for aluminum), I = current (amps), D = one-way distance (feet), and CM = circular mil area of conductor (from NEC Chapter 9 Table 8). Maximum recommended: 3% for branch circuits, 5% total (feeder + branch).