The clay, the kiln load, and what one pot really cost.

Because glaze recipes are conventions, not chemistry homework. A base recipe is meant to be read as percent by weight, nominally totaling 100, with colorants and suspenders as additions beyond it — but book recipes drift: 99.7 from rounding, 347 from an author who never normalized. Scaling off the recipe's own base total is what a working potter does at the scale, and it is what this page does, so any recipe you can read, you can batch. Five thousand grams is a two-and-a-half gallon bucket, which is a more useful answer than five thousand grams.

Because no honest calculator can know either one. Water in a glaze is adjusted to the gravity you slake to — thicker for dipping, thinner for brushing, different for every recipe and every studio's habits. And the published gravity targets contradict each other inside a single application method: Digitalfire quotes 1.4 for a five-second dip and 1.5 for a one-second one, then 1.55 for a dark opaque brushing glaze and 1.25 for a clear. Glazy declines to give per-method numbers at all. Worse, "SG" means two different things between potters — some write 1.55 and some write "155" for the same slurry — so a box asking for it would collect two incompatible numbers and quietly get one of them wrong. Weigh the dry materials from this page, add water past where you think, then adjust to your own gravity.

Nobody's number but your body's, and the published ones disagree. The manufacturer sheets we checked put stoneware at 11–12% — Standard 182 Angel White is 11.0% at cone 6 and 12.0% at cone 10, Laguna B-Mix is 12% at cone 5 — while a widely cited teaching source says 11–13% between cone 6 and cone 9. Both are here because they genuinely differ at the top. Two things those ranges hide: shrinkage moves with the CONE as well as the body — Standard's 130 porcelain goes 10.0% at cone 7 to 12.0% at cone 10 — so one figure per clay is already an approximation; and no sheet says whether its number is drying, firing, or the whole way from wet. Which is why the honest answer comes off a test tile: score a 10 cm mark in wet clay, fire it, measure what is left. Type both sizes into this page and it hands you your body's real rate. Use that one everywhere after.

Because you fire every pot twice. Bisque, then glaze. Almost every figure you will see quoted counts one, which understates the electricity in a pot by about a third. The arithmetic is draw × hours × duty cycle × your rate. L&L publishes the duty cycle itself rather than leaving it to a rule of thumb: divide a low firing into three equal parts and a high firing into four, drawing 25, 50, 75 and — for a high fire — 100 percent of the plate rating. That averages exactly 50% for a bisque and 62.5% for a glaze firing, which is why one shop-wide number cannot hold both. Run it on their own worked example — an 11.52 kW e23T for 12 hours to cone 6 — and you get 86.4 kWh, the figure they print. At the EIA's June 2026 residential rate of 18.34¢ that is $15.85, and thirty mugs to a glaze load makes it about 53¢ each; add the bisque and it is about 70¢. L&L says the rest themselves: the only accurate way is a kilowatt meter, because every firing differs with the load and the age of the elements. One plug-in meter reading replaces the estimate forever.

Your number, and it is worth counting once. Two independent sources report about thirty mugs to a glaze load in a mid-size studio kiln, one of them a potter firing a real 75-litre Skutt. Working it out from shelf geometry gives roughly two and a half times that, because the arithmetic ignores handles, spacing, post height and the fact that nobody tiles a shelf. A bisque holds about twice as much, because greenware can nest and glazed ware cannot touch — which is the whole reason the two firings cost different amounts per pot. That ratio is a field here too.

Nearly double, and this is the sum that pays for the page. The kiln draws what it draws whether it is full or not, so every pot inside a light load carries a bigger share. On the worked example above, thirty of thirty is about 70¢ a piece; twenty of thirty is 97¢; ten of thirty is $1.76. Which turns a vague feeling into a decision the week before a fair: throwing eleven more costs you clay and an hour, and saves 26¢ on every piece already in that load.

Treat electricity as what it is on your Schedule C: a utility expense. The per-piece figure this page computes is for your PRICE — it tells you what a mug really costs to make so you never price below it. Keep the tax categories clean and let the pricing math be honest separately; a books app should never blur the two, and neither should a calculator. Kiln shelves and elements sit on the same line: a $498 shelf is real money, but spreading it across pots is a depreciation judgement rather than craft arithmetic, so it belongs in your expenses, not in what a mug cost.

We are not going to tell you, and the reason is that the authorities disagree with each other and with themselves. Ceramic Arts Network, B2W and Craftybase all land on cost × 2 to wholesale and × 2 again to retail; IKKAI says × 2 to 3 then × 2 — a fifty-percent spread on the retail multiplier — and says outright that the wider band is there to absorb the pieces that fail, which means stacking a separate breakage percentage on top of it charges you twice for the same broken pots. Ceramics Monthly anchors on the Department of Labor's $24.58 average artist wage and then works its own example at $15. The four sources do agree on one thing: wholesale is half of retail. What this page does instead is show your real cost and your margin at your price, plus the one back-solve that is genuinely useful — total price ÷ your hours, which tells you what the run actually paid your hands.