Two threads, different rates
A lockstitch machine builds every stitch from a top thread and a bobbin thread, and they are not consumed equally. The top thread travels the stitch path and is pulled off the cone with slack for the take-up lever, tension discs and the loop that forms round the hook. The bobbin thread sits under the fabric and only takes up part of the same path. The share is stable for a given machine and tension and it is easy to measure: wind a bobbin, weigh it, run a design with a known stitch count, weigh it again.
Because the two rates differ, cones and bobbins run out at completely different points in a run. On the default figures — 8,500 stitches at 2.2 mm average, a 1.35 take-up and a 33 percent bobbin share — one piece takes 28.5 yards of top thread and 6.7 yards of bobbin. A 120 yard bobbin covers a little under 18 pieces, so a 120 garment run winds seven of them. A 5,500 yard cone would cover around 190 pieces, but only if every stitch on it were one colour, which is never the case.
Tails are not rounding error
Every colour change and every jump trim throws away a tail. Nine trims at three and a half inches is 31.5 inches per garment, which is 0.9 yards. Against 28.5 yards of top thread that is three percent — small on a dense left chest, and thrown in the bin before the garment is off the machine. Shrink the design to a 2,000 stitch name drop and keep the same nine trims and the tails become closer to twelve percent, because the tail count does not fall with the stitch count.
The lever is the file, not the thread. Merging colour blocks so a colour is stitched once instead of three times removes trims, and every trim removed is a tail saved plus a couple of seconds of machine time. That is the same edit that shortens the run, which is why it is worth doing even when the thread cost is invisible.
Why the per piece cost is printed to four decimals
Thread on one garment can easily be a fraction of a cent, and rounding it to cents prints zero and teaches you nothing. The page prints four decimals for one piece and a real figure per hundred, because per hundred is the scale at which the number becomes an amount of money you would notice on an invoice. On the defaults it is 5.71 cents a garment and 5 dollars 71 a hundred.
The consequence is worth stating plainly. Thread is almost never the reason an embroidery job costs what it costs — machine time and hooping are. What thread does control is how many times the run stops, and a stop costs minutes of a person, which is the expensive thing.
Buying against the heaviest colour
A four colour design does not split its thread four ways. One colour usually carries the background fill and takes 40 to 60 percent of the total on its own, while a detail colour might take five. Order against the heaviest colour and you have a run that finishes; order the total divided by four and you have three part-used cones and a stopped machine.
The colour breakdown is sitting in your digitising software. Take the heaviest block, divide it by the total, and put that percentage in the form.
Questions people ask
How much thread does 1,000 stitches use?
It follows from your average stitch length and your take-up factor, which is why the page asks for both rather than quoting a rule. At a 2.2 mm average and a 1.35 take-up, a thousand stitches pull about 3.25 yards of top thread off the cone before any trim tails are counted, and a little over 3.3 once the tails on a nine trim design are shared out. Change the average stitch length and that moves proportionally, so the figure to measure first is the average, not the maximum your fill is set to.
How many bobbins will an embroidery run use?
Total bobbin yardage divided by what a bobbin holds, rounded up. The bobbin yardage is your bobbin share of the stitch path, which on the default figures is 33 percent. Measure it once on your own machine by weighing a bobbin before and after a counted design and the rest of the page is arithmetic.
Why did one cone run out before the others?
Because colours in a design carry very different stitch counts. The colour under a background fill can be half the file on its own while a detail outline is a few percent, so buying an equal number of cones per colour guarantees that one empties first. Take the heaviest colour share off your software colour breakdown and buy against that.
Is thread waste from trimming worth worrying about?
As a cost, rarely. As a signal, yes. A high tail share means the file has a lot of colour changes and jump trims, and every one of those is also a stop, a trim cycle and a chance for a bird nest. The page prints the tail yardage next to the stitching yardage so you can see when a file is trim heavy, which is a digitising problem rather than a purchasing one.
Do I need different figures for caps and for flats?
Probably. Tension is set differently for a cap frame, the fabric is stiffer, and the take-up and bobbin share both shift. Keep one set of measurements per job type rather than one for the shop. The page takes about two minutes to re-run once you have the numbers.