Estimating cable footage from reel weight

Weight is the last honest measurement on a reel with no paperwork. It is not exact and it does not pretend to be. Done properly it lands close enough for a buyer to plan a review, which is all an estimate has to do, and it beats an invented length every time.

The method needs two numbers and a scale: the weight of the loaded reel, and the maker's published weight for a thousand feet of that exact construction. Everything after that is subtraction and division, and both are worth doing twice before anyone writes a figure down.

Weigh the loaded reel, then take off the tare

Put the whole reel on a scale, drum and all, and write the reading down. Then find the empty weight of that drum, which is stamped on many steel and plywood reels and listed by the drum maker for the rest. Subtract it and the remainder is cable weight alone.

If the empty weight is not marked, weigh a bare drum of the same type or use the drum maker's figure for that flange diameter and width. Wood and steel drums of the same size are nowhere near each other in weight, so do not borrow a tare from a different drum.

The maker's weight per thousand feet

Cable weight is published per thousand feet for each construction, size and stranding. Use the figure for the exact cable on the reel, not for a nearby size. A step in conductor size, or a change from solid to stranded, moves that figure enough to change the answer.

Divide the net cable weight by that figure, then multiply by a thousand, and the result is footage. Two reels of the same physical size but different metal will not land anywhere near each other, because aluminum weighs far less than copper over the same length at the same ampacity.

Where the arithmetic drifts

Water is the main source of error. A reel that sat in a puddle holds water in the wraps and between the strands, and the scale reads all of it as cable. Wood drums absorb water too, which throws the tare off in the same direction. Weigh a dry reel where you can.

Stop estimating when a counter reading or a meter reading is available. A recorded length beats arithmetic every time, and a reel that was metered during a pull should be described that way. Weight is the fallback, not the first choice.

Most contractor yards here have a forklift scale or a platform scale near the gate, and a public scale on the highway will do at a push. Weigh the reel where it sits, before it is moved, so the drum does not pick up a fresh load of mud on the way.

Storage conditions change the arithmetic more than the geography does. Reels kept on pallets under cover in a Pflugerville warehouse weigh what the tag says. Reels that sat on bare ground through a wet spring near the Colorado River do not.