Free tool
Cable length calculator
Turn a measurement off the drawing into the length you actually order. Add the vertical drops, a slack percentage for the route you cannot see, service loops, and termination tails, then multiply across your runs and price it. Free, and nothing leaves your browser.
Per run
41.2 m
Total for 4 runs
164.8 m
Cable cost
€ 206
Routed path
36 m
After slack
39.6 m
Slack applies to the routed path only. Service loops and termination tails are fixed lengths, so they are added afterwards rather than inflated by the percentage.
Order by the drum, not the metre. Round the total up to the next standard drum length and keep the offcuts: a run that lands 200 mm short costs a whole new pull.
The plan length is never the order length
Measuring a run on a floor plan gives you a straight line in two dimensions. The cable has to climb into the void, cross at right angles along containment, drop to the outlet, and leave enough tail to terminate twice if the first attempt goes wrong. Every one of those adds metres that the drawing does not show.
What goes into a real run
- Horizontal distance along the containment route, not the diagonal across the room.
- Every vertical section: ceiling void height, drop to the outlet, rise into the rack.
- Slack for route uncertainty, typically 10 percent surveyed and 20 percent estimated.
- Service loops at each end so equipment can be pulled without a re-pull.
- A termination tail per end, usually 0.3 m, more behind a patch panel.
Underestimating here is expensive in a way that does not show up until install week. A run that lands short is not a small overrun, it is a fresh pull with the labour done twice, often through containment that is already full and closed up.
Quoting a full job? Avitly takes cable lengths straight off the calibrated floor plan, including the vertical drops, and prices them per metre on the quote, so the length you estimate is the length you bill.
Common questions
How much slack should I add to a cable run?
Ten percent is the common allowance for a straightforward route with known containment. Push it to 15 or 20 percent when the route is uncertain, the building is old, or you are working from a drawing rather than a survey. Slack covers the difference between the straight line on the plan and the real path around beams, ducts, and fire barriers, which is never shorter.
Why is the cable always longer than the distance on the drawing?
A plan is a flat view. It does not show the drop from ceiling void to socket, the rise from floor box to rack, the detour around a structural beam, or the fact that containment runs at right angles rather than diagonally. Add every vertical section, then add slack for the horizontal detours you cannot see yet. On a typical install the real length is 20 to 40 percent above the plan measurement.
What is a service loop and how long should it be?
A service loop is deliberate spare cable coiled at a termination so equipment can be pulled out, moved, or re-terminated without a new pull. Half a metre at each end is normal for a wall plate, one to two metres behind a rack or above a ceiling-mounted display. It costs almost nothing at install time and saves a full re-pull the first time someone swaps a device.
Should I calculate each run separately or in total?
Calculate a representative run, then multiply by the count, which is what this tool does. Order against the total, rounded up to the next drum size. Buying by the drum rather than the metre is nearly always cheaper, and the offcuts cover the run that turns out longer than surveyed.
Does slack apply to service loops too?
No, and this is a common double-count. Slack is a percentage of the routed path because route uncertainty scales with distance. Service loops and termination tails are fixed lengths you have already decided on, so applying the percentage to them inflates the estimate. This calculator applies slack to the routed path only, then adds the fixed allowances.
How do I estimate cable before I have a floor plan?
Use the room perimeter as a rough proxy for the containment route, add the ceiling void height for each drop, and apply 20 percent slack rather than 10 because you are estimating rather than measuring. Flag it clearly as budgetary. The moment you get a scaled plan, re-measure, since cable is one of the easiest lines to lose money on when the survey comes in longer than the guess.
This is built into Avitly. Same maths, running on your real project instead of numbers you retype.
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