How to estimate remaining footage from reel weight
Weighing a part reel is often the only measurement a seller has. Here is the arithmetic we use, where it drifts, and how to present a weighed figure beside a tag figure.
A part reel on a platform scale
Most reels that leave a plant are part reels, and most part reels have lost the paperwork that would say how much is on them. The crew knows roughly. The tag says what was shipped. Nobody wrote down what came back. In that situation a scale is the most honest instrument available, provided everyone understands what it can and cannot tell you.
The method is simple and the tolerance is not. A weighed figure is an estimate built on a nominal catalog weight, and it inherits every source of error between the two. Sellers get into trouble not by weighing but by presenting the result as a measurement. Send the figure with its method attached and it becomes useful evidence rather than a number to argue about.
At a glance
- You need
- Gross weight and reel tare
- Then divide by
- Published lb per 1,000 ft
- Expect
- A tolerance, not an exact figure
- Ideal case
- Weight plus a counter reading
Weigh the reel, subtract the tare, divide
Put the loaded reel on a platform scale and write down the gross weight. A large wooden reel will not fit on a bench scale, so use a truck scale and weigh the vehicle with the reel and again without it, or weigh the loaded trailer against a known empty weight. Record pounds rather than a rounded tonnage, because the arithmetic downstream is sensitive to what you drop at this step.
Subtract the tare. That figure is the empty reel weight stenciled on the flange, and it covers the wood, the lag bolts and the arbor plates. If the stencil has gone, weigh an empty reel of the same size or look up the reel maker's figure by diameter and width. Do not substitute a guessed figure for a few tens of pounds, because on a short remnant that guess is most of the answer.
Divide the net weight by the published weight per foot for that exact construction. Catalogs and standard tables give weight per thousand feet, and the figure changes with conductor metal, size, insulation, armor and conductor count. Divide the thousand-foot figure by a thousand and you have pounds per foot. The result is an estimate of length, and it is worth labeling as one at the moment you calculate it, with the catalog figure written beside it.
- Weigh the loaded reel and record the gross figure in pounds
- Find the tare stenciled on the flange, or weigh an empty reel
- Look up lb per 1,000 ft for the exact cable construction
- Subtract tare from gross, then divide by pounds per foot
- Write the result down as an estimate with the tolerance stated
The scale gives you a weight. The catalog turns it into a length, and the tolerance is yours to carry.
Why the answer is only an estimate
Catalog weights are nominal. Insulation and jacket walls are made within a tolerance, bedding tapes and fillers vary between production runs, and the published figure is an average for the construction rather than a certificate for your reel. Add the difference between one maker's compound and another's, and the answer is already a few percent away from the truth in either direction before the reel itself is considered. That is the floor of the error, not the whole of it.
The reel introduces most of the remaining error. Wood takes up water, so a reel that has stood outside for a season weighs more than the tare stenciled when it was new, and the extra weight reads as cable. Mud, snow and ice packed into the flange do the same. Clamps, staples and a steel pulling grip left on the end add a little more that belongs to nothing at all.
Short remnants are the worst case in relative terms. On a 2,000 ft reel an error of twenty pounds disappears into the total. On a fifty foot remnant that same twenty pounds is a large share of the answer. This is one reason we treat a weighed figure for a short length as a ceiling, and why a tape measure is often the better instrument once a reel is nearly empty.
Cases where a tape beats the scale
If the remnant is short enough to lay out, measure it. A hundred feet can be walked along a marked aisle or run between two marks in the yard with a tape, and what you get is a measurement rather than an inference. On large conductor, where every foot carries real value, the walk is worth the time it takes and the second person it takes to keep the cable off the ground.
The counter at the arbor is the other measurement. Where a reel carries one, the readings at the start and end of the last pull give the length taken, and the difference against the nominal length gives what remains. Counters drift and crews forget to record them, so treat the reading as evidence of the pull rather than as an audit of the reel, and say which pull it came from.
Do not weigh when the reel is full and the tag is intact. If a sealed reel still carries its label and the wrapper is unbroken, the nominal length is better information than any scale will produce, and re-weighing only introduces doubt where there was none. Weighing earns its place on opened reels with no reliable record of what came back from the job, and on those the figure is worth having even with a wide tolerance.
Report both figures and say which is which
Give us the tag figure and the weighed figure separately, and say how each was obtained. A reel tagged at 1,000 ft with 180 ft recorded as pulled implies 820 ft left. If the scale says 780, we want both numbers with the method written beside each. We will price from the lower one and tell you that we have done so, so that nothing is hidden at the point of agreement.
Do not average the two silently and do not present the weighed figure as a measurement. A buyer who later finds the reel short by the difference will discount everything else you send, and the desk will remember the lot when the next one arrives. An estimate labeled as an estimate costs nothing. An estimate dressed up as fact costs the working relationship. Say which one you would trust in our position, and why.
If you have no scale and no counter, say that as well. A reel with a tag, a visible wrap count and a photograph of the flange can still be reviewed, and a buyer can apply a judgment to what is left. The one thing we cannot work with is a number whose origin nobody can explain, because then the only remaining option is to price the lot at the bottom of the range.
Two figures, each with its method, beat one confident number every time.
Questions about weighed footage
Where do I find the weight per thousand feet for a cable?
Start with the manufacturer's catalog page for the exact construction, then the standard tables published for the cable type. The figure depends on conductor metal and size, insulation and jacket, armor, and conductor count, so a generic number for the size will be wrong. If the maker is gone, the type letters and size on the jacket print are usually enough to match a table entry.
Can I weigh a reel on a truck scale?
Yes, and for large wooden reels it is often the only practical option. Weigh the truck or trailer empty, then loaded, and take the difference. Public scales are usually certified and print a ticket, which is useful evidence. Do both weighings close together with the same fuel load, because fuel, passengers and tools otherwise show up in the answer as cable.
Should I use the tag figure or the weighed figure?
Use both and label them. The tag figure is what was shipped, adjusted by any recorded pull. The weighed figure is an estimate of what sits on the reel now. Where they disagree, the lower one is the working number until somebody measures the cable. We will say which figure we priced from, and a counter reading usually settles the question.
What if the reel tare is not stenciled anywhere?
Weigh an empty reel of the same diameter and width, or ask the reel maker for the bare weight by size. Reels of the same nominal size are close enough for an estimate, though not identical. If neither is possible, treat the whole calculation as rough, tell us so, and consider measuring the cable instead. A guessed tare on a small remnant can be wrong by more than the cable weighs.
Other seller guides
- Reading a reel tagWhat the markings on a flange actually tell a buyer
- Copper and aluminumTwo conductor metals, and how to tell them apart
- ACSR and AAACSteel-cored and all-alloy overhead conductor
- High voltage safetyWhat not to touch before the clearance is issued
- Storing conductorKeeping reels saleable between projects
Send us your reel list
Six details are enough for a first review: what the cable is, the metal, the size, the footage or reel count, the condition and where it sits. Photographs can follow by text or email. There is no fee and no obligation, and nothing moves until written terms are agreed.
Ready to send the reel list?
Six details are enough for a first review: what the cable is, the metal, the size, the footage or reel count, the condition and where it sits. Photographs can follow by text or email. There is no fee and no obligation, and nothing moves until written terms are agreed.
Send the weights you have
Give us gross weight, tare, construction and any counter readings, and say which figures are measured and which are estimated.
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