Size 11.75 just walked in. The printed chart stops at 11.
US size resolves to inside diameter, the neutral-axis formula gives the exact length to saw, wide bands upsize by the convention you choose, and the blank prices itself at your per-gram stock cost. Everything stays in your browser.
The ring
The numbers here are yours to check. This page does arithmetic on what you type — it cannot see your recipe, your equipment or your batch.
Want it to remember?
In MadeKeeper your sheet and wire stock is inventory by the gram: each ring consumes its blank's real weight at your real cost, and the finished piece knows what the silver in it cost. See for metalsmiths or poke around the live demo. $19/mo for the whole back office, kept for as long as you stay. The shop stays free for cost a piece and one fair — no product cap. The tax packet, Etsy and Square, and more fairs are the $19.
The chart taped above the bench, for every size
Every ring starts as a sawn strip, and every silversmith has the chart taped above the bench — until a customer lands between its rows. The math below is the same math the calculator runs.
What formula does this use?
The bench classic: blank length = (inside diameter + stock thickness) x pi. Adding the full thickness to the diameter measures the band along its neutral axis — the centerline that neither stretches nor compresses when you bend the strip round — which is why the formula holds for thin wire and heavy stock alike. It is the same arithmetic behind every printed supplier chart; the charts just pre-computed a few dozen cells of it.
Why do the printed charts disagree with each other by a little?
Because US size-to-diameter tables themselves disagree by about a tenth of a millimeter, and some charts bake in a filing allowance while others don't. This calculator uses the ISO-derived US table (size 7 = 17.32 mm inside diameter) and leaves the allowance at zero unless you set one — so the number you get is the formula, undoctored, and any adjustment is visibly yours.
Why does a wide band need to be cut a size larger?
A wide band touches more finger, so it fits tighter than a thin band of the same inside diameter — past roughly 6 to 8 mm of width, suppliers recommend upsizing. How much is argued: a half size is the common advice, a full size for very wide cuffs. The default here adds a half size at 8 mm and both numbers are settings, because your customer's knuckle outranks anyone's chart.
How does the metal weight and cost work?
The cross-section depends on the stock you actually buy: flat is width x thickness, a half-round is pi x width squared / 8, and a low dome runs about two-thirds of width x height. That area x the blank length x a density gives grams; your own per-gram stock price turns grams into money. The densities are seeds you can change, and here is where each came from: copper, red brass and jewelry bronze from the Copper Development Association's own alloy pages (C11000 8.91, C23000 8.75, C22600 8.78), silver from the Royal Society of Chemistry at 10.5. Sterling and the karat golds are alloys whose density the alloy maker sets, not the karat, so those are seeds too and yours wins. The PRICE is never ours to guess, because you bought the stock and the receipt is sitting in your drawer.