How much cable raceway or trunking you need, piece by piece

How the raceway is worked out

You add up the straight runs of the route, cut the channel for each run between two corners, and count the fittings on their own: one elbow at every turn, one coupling wherever a run is longer than a section, and an end cap at each end.

The number of sections comes from a cutting plan. Each straight run takes as many whole sections as fit, and the leftover pieces go into sections you have already started, wherever there is room. The calculator compares that with the route length plus the cutting waste and buys the larger of the two. The waste starts at 5% as a margin for a bad cut; raise it if this is your first raceway.

There are three kinds of corner. An inside elbow turns into a corner of the room, between two walls or between wall and ceiling. An outside elbow turns around a corner that sticks out. A flat elbow changes direction on the same wall, for example where the drop from the TV meets the run above the baseboard. On each row, enter one straight run and the corner that ends it. If you put several corners on one row, the calculator splits the row into equal parts, so for an accurate cutting plan use one row per straight run.

With screws, the calculator puts one at least every 24 in and one at each end of every section, next to the fittings, as mini trunking makers such as Elettrocanali ask. Extension cords are as long as the route plus the cord left outside the channel at both ends, rounded up to the whole foot.

Worked example: TV cords down to the outlet

These are the American values the calculator opens with: 4 ft down from the TV with a flat elbow at the bottom, 8 ft along the wall to an inside corner, then 6 ft to the outlet. A 1" × 1/2" peel-and-stick channel in 5 ft sections, 5% waste.

• Route: 4 + 8 + 6 = 18 ft; with the waste 18.9 ft, or 3.78 sections: 4 sections of 5 ft
• Cutting plan: section 1 gives 4 ft and 1 ft, sections 2 and 4 go on whole, section 3 gives the last 3 ft of the 8 ft run. The plan also needs 4 sections.
• Fittings: 2 couplings (the 8 ft and 6 ft runs are longer than a section), 1 flat elbow, 1 inside elbow, 2 end caps

With screws every 24 in you need 16 screws and anchors. One extension cord with 3 ft left outside the channel needs 18 + 3 = 21 ft.

In the UK, in metres: 1.2 m, 2.5 m and 1.8 m with 2 m lengths of 20 × 10 mm trunking make a 5.5 m route, 5.775 m with the waste, so 3 lengths, 1 coupler, 1 flat bend, 1 internal bend and 2 end caps.

Which size: how many cables fit

The size does not change the number of sections or fittings, but elbows, couplings and end caps must match it. Makers give guidance like this:

Channel	Cables, as stated by the maker
16 × 8 mm	one flexible cable up to 6 mm across (D-Line Micro)
20 × 10 mm	1 or 2 flexible cables, such as lamp, speaker or phone (D-Line Micro+)
1" × 1/2"	two power cords at most, four cables in all (Wiremold CordMate II)
50 × 25 mm	several cables, such as a wall-mounted TV (D-Line Maxi)

With a hinged cover you lay the cable in and snap the cover shut, as both D-Line and Wiremold describe, so plugs never have to go through the channel. If you are between two sizes, take the larger one.

Sections, fittings and fixings on sale

In the US, the Wiremold CordMate II channel (C50) is 60 in long, and the C210 kit holds 12 ft in three 4 ft sections with 2 flat elbows, 1 inside elbow, 1 outside elbow, 2 couplings and a T-fitting. Not every cord cover system makes end caps; if yours does not, skip that line. In the UK and Europe, mini trunking usually comes in 2 m lengths, such as the self-adhesive HellermannTyton HTA2010. Enter the section length you find in the store.

The calculator does not count tees: if the route branches, work out the branch on its own and add a T-fitting. Even when the channel has adhesive backing, Wiremold tech support advises screws as well, chosen for your wall, and the instructions ask for a clean wall without texture.

Cord covers are for plug-in cords, extension cords and low-voltage cables. Wiremold states that CordMate II is not NRTL listed and must not be used to extend hard-wired wiring. A new outlet or a new circuit is a job for an electrician; in England, Approved Document P makes a new circuit notifiable building work.

Common mistakes

• Dividing the whole route by the section length. Each run between two corners is cut on its own and the offcuts do not always fit elsewhere, so the cutting plan can need one more section.
• Forgetting couplings. A straight run longer than a section needs one coupling for each extra section.
• Mixing up inside and outside elbows. Inside when you turn into the corner of the room, outside when you go around a corner or a column.
• Fittings of another size or brand. Elbows and couplings are made for one channel profile.
• Adhesive alone on a textured or dusty wall. It peels off: clean the wall or add screws.
• Using a cord cover for permanent wiring. New circuits and outlets are an electrician's job.