How it works
Add a group for each repeated route length. An unused group has zero runs. Slack is the total extra cable across both ends of each run, not the allowance at each end. The percentage adds further length to every planned cut for measurement uncertainty, trimming and handling. The calculator then places whole continuous cuts onto equal-length spools. It never joins leftovers to make a longer run. Its longest-first packing method provides a practical suggested plan; it is not an exact optimizer for the smallest possible spool count.
The formulaPlanned cut = (route length + slack) × (1 + cut allowance % ÷ 100)
Total cable = sum of (runs × planned cut)
Spools: sort cuts longest first; place each into the first spool with enough remaining cable
Put it into practice
EXAMPLEFive 40 ft routes and three 70 ft routes, with 10 ft of slack per run and 10% cut allowance, require five 55 ft cuts and three 88 ft cuts: 539 ft total. They fit on one 1,000 ft spool, leaving 461 ft unallocated.
EXAMPLEThree 60 m cuts with no added slack or allowance cannot fit on two 100 m spools, even though 180 m is less than 200 m. Each continuous cut needs its own spool, so the suggested plan uses three spools.
Good to know
Why can the result exceed total length divided by spool length?
Leftover pieces may be too short for the next continuous run. The calculator accounts for that fragmentation. A planned cut longer than a spool is rejected; buy a suitable spool or revise the design instead of assuming a splice.
Does this check Ethernet distance limits?
It flags a route plus slack longer than 100 m before patch leads. Standard twisted-pair Ethernet channels are generally limited to 100 m including patch cords; fixed-cabling allowances and equipment restrictions can be shorter. A run below this warning threshold is not a compliance result. Check the complete channel design and test the installed link.
Are patch leads, connectors and installation ratings included?
No. Count patch leads, jacks, patch-panel ports, terminations and spare components separately. Cable category, conductor material, fire rating, environment, bundle heating and PoE suitability must match the installation. This is a quantity estimate only.
What are the input limits?
Up to 300 runs per group and three groups are supported. Zero runs gives zero cable and zero spools. Lengths must be positive for active groups. The purchase result uses whole spools of the entered length; existing offcuts and reels of different lengths are not included.