How to Estimate Wire for a Whole House
The most reliable way to estimate wire for a house is to work from the circuit count rather than from square footage alone. Square footage gives a ballpark, but the real driver is how many circuits you have and how far each one runs from the panel. A simple method gets you close enough to order with confidence.
The Estimation Method
Start by counting the circuits on the panel schedule. Estimate the average one-way run length from the panel to the center of each circuit, which in many homes lands somewhere between 30 and 60 feet. Multiply the circuit count by that average run, then add 15 to 20 percent for slack at boxes, vertical drops, and normal waste. Do this separately for each wire gauge, since lighting and outlet circuits use different sizes.
Typical Quantities by Gauge
A typical new home has 20 to 40 circuits and commonly uses these gauges:
| Wire | Common Use |
|---|---|
| 14/2 NM-B | General lighting and 15-amp circuits |
| 12/2 NM-B | 20-amp receptacle, kitchen, bath, garage circuits |
| 14/3 and 12/3 NM-B | Three-way switches and shared-neutral circuits |
| 10/2 NM-B | Water heater and 30-amp dedicated circuits |
| 6/3 and 8/3 | Range, dryer, and large appliance circuits |
Across all of these, an average home can use several thousand feet of cable in total, with 12/2 and 14/2 making up the bulk of it.
Buy in 1,000-Foot Spools
For the gauges you use most, 14/2 and 12/2, buying 1,000-foot spools costs far less per foot than short 25 or 50-foot rolls. Use 250-foot rolls for the gauges you need in smaller amounts, such as 10/2 or three-conductor cable. Ordering by the spool also means fewer splices and a cleaner job.
A Note on Accuracy
This method gives a solid working estimate for ordering. For an exact material takeoff, an electrician measures each run from the plans. Ordering a little extra is normal and avoids a job stopping for one short run.
IB Lighting stocks Southwire and CerroMax by Cerrowire in 1,000-foot spools and smaller rolls in our electrical wire and cable collection, with free freight plus free freight insurance on every order. Call (800) 674-9019 for bulk pricing on a whole-house package.