Fly Tying Material Calculator
Tell it the hook size, the kind of fly and how many you want to sit down and tie. It works out the thread, dubbing, feathers and wire the batch will eat, and how many spools and packets that means buying. Nothing uploaded.
Shopping list
Where the thread goes, per fly
Hackle
Dubbing
What it is measuring
Learn more: working out fly tying materials by wrap count
Thread is counted in turns, not guessed at
Nothing here works from a table of how much thread a pattern uses. It counts the turns the fly needs and multiplies each one by the distance it travels around the hook.
A turn is the circumference of whatever it is going around, so a wrap on a bare size 12 shank of 0.41 mm wire with 0.067 mm thread is about 1.50 mm of thread. Wraps over a dubbed body travel further, because the body is fatter than the wire.
Take a size 12 dry fly in 140 denier. The shank is 9.4 mm, and touching turns of a thread 0.202 mm wide need 47 of them to cover it, which is 70.5 mm of thread for the base layer alone.
The dubbed body adds 11.1 turns at 0.61 mm of rope diameter each, and those turns go around a 1.02 mm circle rather than the 0.48 mm one the base layer had, so they cost 35.5 mm. Four tie-in points at five wraps each add 30.0 mm, the head and whip finish add 23.1 mm.
That comes to 159 mm on the hook. The default 60 mm allowance for the tag you pull off and trim takes it to 219 mm, or 8.6 inches a fly.
A hundred of them, with the 10% waste allowance on top, is 26.4 yards. One 100 yard spool, and you are nowhere near the end of it.
Denier tells you the weight, not the thickness
This is the part most charts get wrong, and it matters because thread width is what decides how many turns cover a shank. The Global FlyFisher thread table puts it bluntly: denier and thickness are not correlated.
Denier is defined on that same page as the weight in grams of 9000 metres of thread. That fixes the amount of fibre in the cross section and nothing else.
Their measurements bear it out. Veevus 6/0 and Veevus 8/0 are both 110 denier but measure 0.065 mm and 0.059 mm. UNI 6/0 at 135 denier measures 0.075 mm, while Benecchi Fine 8/0 at a heavier 150 denier measures only 0.056 mm.
The cross section explains it. At a nylon density of 1.14 g per cubic cm, 150 denier works out to 0.0146 square mm of fibre. Spun flat at a five to one width to thickness ratio that is a ribbon 0.27 mm wide and 0.054 mm thick, which is within a few percent of Benecchi's measured 0.056 mm.
Run the same sum on UNI's 135 denier against its measured 0.075 mm and the implied ratio is closer to two to one, a rounder thread. So the "how the thread lies" setting in the advanced panel is not a cosmetic choice. Flattening the same spool makes it cover more shank per turn and changes the yardage.
Hook size is the loosest number in the whole thing
Every dressing dimension here scales off shank length, so the hook table matters more than anything else. It is also the least standardised thing in fly tying.
Global FlyFisher's hook page says that little, if any, standardization exists today within the hook manufacturing fraternity, and measurements back that up. A thread on the Troutnut forum measuring hooks against a rule lists the Mustad 94845 dry fly at 8.5 mm in a size 12 and the Tiemco 100 at 10 mm in the same size.
That is a full size of disagreement between two standard dry fly hooks. The built-in figures here sit between the two, and the shank override in the advanced panel exists so you can measure your own and stop arguing with the table.
Gape comes out of the shank rather than a second lookup, using the usual definition that a standard shank is twice the gape plus the width of the eye. For a size 12 that lands at 4.25 mm.
Dubbing weight is an estimate, and here is how to tighten it
The dubbing figure is built the same way as the thread figure. A rope wound in touching turns is a stack of small rings, each holding its own cross section of dubbing over the distance it travels.
A size 12 dry fly body at medium build works out to 10.4 cubic mm of packed dubbing. Turning that volume into a weight needs a density, and that is where the certainty ends.
The default is 0.15 g per cubic cm, which puts a size 12 dry body at 1.56 mg and a hundred of them at 0.16 g. Compare that to a 2 g packet and you can see why a bag of dubbing seems to last forever.
If you want the number to be yours rather than an assumption, tie twenty bodies, weigh the dubbing before and after on a 0.01 g scale, and divide the difference by twenty times the cubic mm figure this shows. Then put the result in the advanced panel.
Feathers, and why saddles cost what they do
Hackle is counted as stem length rather than feathers, because a turn of hackle is a turn around the finished body just like a turn of thread.
Six turns around the 1.63 mm body of a size 12 dry fly uses about 3.4 cm of usable stem. Against the 6 cm of usable stem assumed for a size graded cape feather that is 1.8 flies, and against the 18 cm assumed for a saddle hackle it is 5.4.
Those two assumed lengths are the model's own, not a published standard, and a really long genetic saddle will beat them. The ratio between them is the point: a saddle covers several flies per feather where a cape covers one or two, which is most of the reason the two are priced the way they are.
FAQ
How much thread does one fly use?
For a size 12 dry fly in 140 denier thread the model here comes to about 219 mm, or 8.6 inches, and roughly a quarter of that is the tag you pull off and trim rather than anything that ends up on the hook. The number moves with hook size and with how much of the shank you cover, not with the pattern name. A hundred of those flies with 10% waste on top is 26.4 yards, so a single 100 yard spool covers the batch with room to spare.
Does a higher denier thread mean a thicker thread?
No, and the Global FlyFisher thread table says so directly: denier and thickness are not correlated. Denier is the weight in grams of 9000 metres of thread, which fixes how much fibre is in the cross section but says nothing about the shape it is spun into. The same 110 denier Veevus is listed at 0.065 mm in one size and 0.059 mm in another, because a thread spun flat lies wide and thin while a corded thread of identical weight sits closer to round. That is why this calculator asks how the thread lies as well as what denier it is.
How many flies can I tie from one hackle feather?
It depends on whether the feather came off a cape or a saddle, and on how fat the body underneath it is. Six turns of hackle around the 1.63 mm body of a size 12 dry fly uses about 3.4 cm of usable stem, which is roughly one and three quarter flies from a 6 cm cape feather and about five from an 18 cm saddle hackle. Cape feathers are graded by size and short, saddle hackles are long and cover several flies each, which is the whole reason saddles cost what they do.