How much wire to order: a quick takeoff
Published Sep 30, 2026
Ordering too little wire stops a job; ordering too much leaves you with a partial spool you paid full price for. A quick takeoff before you order gets you close, and knowing when to buy a cut and when to buy a full spool saves money on top of that.
Step 1: measure the route, not the distance
Measure the path the wire actually takes: up the wall, across the ceiling, around beams and down to the device. A run that is 40 ft in a straight line is often 60 ft by the raceway. For a conduit job, measure the conduit, then add each vertical drop.
Step 2: add the extra at each end
NEC 300.14 requires at least 6 in. of free conductor at every box where it is spliced or connected, and where the box opening is less than 8 in. across, at least 3 in. has to reach outside the opening. In practice most electricians leave 8 to 12 in. at a device box and more at a panel, where the conductor has to reach its breaker or lug.
A simple rule: add 2 ft per box and 3 to 6 ft at the panel, more for a large panel where the breaker is far from the entry.
Step 3: multiply by the number of conductors
In conduit, each conductor is a separate wire. A 120/240 V circuit with two hots, a neutral and a ground is four conductors, so a 60 ft conduit run needs 4 x (60 ft + ends) of wire. Order by color:
| Conductor | Color | Length for a 60 ft run with 6 ft of ends |
|---|---|---|
| Hot | Black | 66 ft |
| Hot | Red | 66 ft |
| Neutral | White | 66 ft |
| Ground | Green | 66 ft |
With cable such as NM-B, UF-B or SER, you order the cable once, because the conductors are inside it.
Step 4: add a margin
Add 10 percent to the total for waste, a pull that goes wrong and small changes on site. On long pulls with many bends, add more.
Cut to length or full spool?
| Situation | Better choice |
|---|---|
| One run, one or two colors | Cut to length |
| Several runs of the same size and color | Full spool |
| Large conductors for a single feeder | Cut to the exact length |
| Stock for the van or the shop | Full spool |
| A color you rarely use | Cut to length |
Where a product is sold both ways, its page prices the cut and each spool size, so you can compare them before you order. Two things to keep in mind:
- Cut wire is final sale. It is made to your length and cannot be returned, so measure twice. Uncut spools can be returned under the terms on our returns page.
- A cut adds a business day to the ship date shown on the product page.
Worked example
A 100 A feeder from a main panel to a subpanel in a detached shop. The conduit route is 85 ft, with 6 ft of ends at the main panel and 4 ft at the subpanel. The feeder is two hots, a neutral and an equipment ground.
- Length per conductor: 85 + 6 + 4 = 95 ft
- Add 10 percent: about 105 ft
- Order: 105 ft each of two hot conductors and the neutral, plus 105 ft of the ground size
The sizes come from the load calculation and NEC Table 310.16; for a comparison of copper and aluminum for a feeder like this, see aluminum vs copper feeders. On a run this long, check voltage drop too with the voltage drop calculator.
Shop by the foot or by the spool
- 12 AWG THHN/THWN-2 and 10 AWG in every common color
- 2 AWG XHHW-2 aluminum and 1/0 XHHW-2 aluminum for feeders
- 12/2 NM-B and 12/2 UF-B
The allowances above are common practice, not code requirements, except where a section of the NEC is cited. Your job conditions and local rules decide the final numbers.