Estimate cable boxes by calculating total pathway footage, adding service-loop/waste allowance and rounding the final box count up.
Basic formula
Total cable = number of runs × average actual pathway length × (1 + waste allowance). Then divide by the footage in each box/reel and round up.
Example
Forty-eight runs averaging 90 feet equals 4,320 feet before allowance. With 12% extra, the planning quantity becomes about 4,838 feet. With 1,000-foot boxes, order at least five boxes.
Why installers may order more
Parallel pulls can require multiple boxes at the same time. A job may therefore need more boxes on site than the pure footage minimum even if leftover cable is used later.
Avoid straight-line estimates
Measure pathways through ceilings, corridors, risers and racks whenever possible. The cable does not travel through walls in a straight geometric line.