Know what every bar costs before you cut.
One calculator, not six. The mold says how much oil the batch takes, the oils say how much lye and water, the bars you want scale it all, every bar carries its true cost and what you keep on each channel, and the cure rack puts the pour on the calendar. Change one number and the rest rolls. Your recipe stays in your browser.
The mold
Inside measurements, in inches. The batch is sized to the mold, not the other way round.
The oils
Weights by weight, never volume — in soap, the scale is the law. SAP values come from two published charts (sources in the footnote); jojoba is really a wax and mostly escapes saponification, which its low value reflects.
Lye, water & the loaf
NaOH bar soap. For liquid soap (KOH) the liquid soap calculator runs the same shelf.
Lye is caustic — gloves on, eyes covered, and always lye into water, never water into lye. Run any new recipe through a second calculator until you trust this one; good soapers double-check everything.
Where these numbers come from: the mold rule and its 0.36–0.38 variants (Soapmaking Forum, Modern Soapmaking, Classic Bells), fragrance at 3–6% of oil weight under each oil's IFRA category-9 ceiling (Lovin Soap, Bramble Berry's fragrance calculator, Lovely Greens), milk for water frozen with the lye added over fifteen minutes or more (Soap Queen, Lovin Soap), all read Sep 3, 2026. The math is the same the lye calculators at SoapCalc, Bramble Berry and Soapmaking Friend run; the SAP charts are cited in the footnote.
What the batch costs you
Materials priced as what goes into the pot. Water is free; your time is not, so it gets its own line.
The cure rack
Soap exists the day you pour it and becomes sellable weeks later. Put the pour on the calendar, not in your memory — and, with your shop loaded, against your next fairs.
Your recipes export any time — that button is a promise, not a feature. MadeKeeper learned from Soapee, the free recipe site that shut down April 30, 2024 and took makers' saved formulations with it. What you build here leaves with you.
madekeeper.com/soap-lye-calculator — SAP values and fee rates checked July 29, 2026
SAP sources: the published saponification charts at From Nature With Love (fromnaturewithlove.com/resources/sapon.asp) and Certified Lye (certified-lye.com/lye-soap.html), checked July 29, 2026. Values are of NaOH per ounce of oil; where the two charts differ the lower value is used, which errs toward more superfat, never less. Fee rates as of July 29, 2026: Square in-person 2.6% + 15¢ (Square's published pricing); Etsy $0.20 listing + 6.5% transaction + 3% + $0.25 US payment processing (Etsy's Fees & Payments Policy). Simplified honestly: Etsy's transaction and processing fees also apply to shipping you charge, and Offsite Ads (12–15% when they bring the sale) aren't included. Booth uses Square's free-plan card-present rate; a booth or table fee is its own cost — this page prices the bar, and the fair profit calculator prices the day.
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.
This is one calculator, not six.
The mold feeds the oils. The oils feed the lye, the water and the milk. The bars you want scale all of it, one bar's share of the pot feeds its true cost, the cost feeds what you keep on every channel, and the pour date feeds the cure rack. Change the olive or the superfat and everything below rolls — the same way the app rolls when you import a recipe and adjust one number. Bath bombs, lip balm and liquid soap draw from the same shelf: bath bombs, lip balm, liquid soap.
In your shop it is the same calculator with your rows behind it. Your shelf answers before you weigh: “you can make 60 bars of the Lavender CP bar with what's on the shelf — 60 more would need olive, coconut and lavender,” with the numbers. The cure rack reads your fairs and says which ones this batch is cured for. The batch lands in Make with How many already filled in and the lye helper open on your oils. A web calculator cannot do any of that, because it has never seen your shelf. $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 lye math soap makers actually ask about
Every lye calculator on the internet will hand you a NaOH weight. Almost none will tell you what the bar cost you, none will tell you what you keep after Square or Etsy takes its cut, and none of them has ever seen your shelf or your fair calendar. That gap is where underpricing lives. A $7 bar that costs $1.40 in materials looks comfortable until the fees, the labor, and six weeks on the rack each take their bite. The math below is the same math the calculator runs; do it once by hand and you'll never guess at a price again.
What does superfat actually do?
Superfat is lye you deliberately leave out. At 5%, the convention most calculators default to, the lye saponifies 95% of your oils and the last 5% stays free in the bar — a margin of safety against a measuring slip and a little conditioning on the skin. Coconut-heavy recipes often run higher because coconut's cleansing bite wants softening. The calculator takes the superfat off the lye; it never adds oil.
What's a water discount, and why does the default matter?
Water is only there to carry the lye into the oils, and all of it leaves during the cure. Old-school full water is around 38% of your oil weight; a working discount of 33% traces faster, unmolds harder, and cures sooner. Too little and the batch seizes on you. The calculator takes either a percent of oils or a water-to-lye ratio, because soapers think in both.
How much oil does my mold hold?
Multiply the inside length, width and height in inches, then by 0.40 — that is the ounces of oils the batch should carry. The rule was built for full water and a usual superfat, so with a water discount or room for additives makers use 0.36 to 0.38. On this page the factor is a setting you own, and one tap scales your oils to the mold.
Can I use goat milk instead of water?
Yes — milk replaces some or all of the water phase by weight, and the lye needs the same total liquid either way. Freeze the milk to a slush and add the lye a little at a time over fifteen minutes or more so it never scalds and never scorches the sugars. The calculator splits the liquid into milk and water at the share you set and prices the milk on the bar.
Why do SAP values differ between calculators?
Because oils are agricultural products, not lab reagents. A saponification value is measured from real fat, and it moves with the crop, the season, and the refinery. Two honest charts can disagree by a point or two; this page ships the lower value where they differ, which errs toward more superfat and never toward free lye.
What does the 4–6 week cure cost me?
Cash on the rack. A loaf poured today is real money — oils, lye, fragrance, bought and paid for — that can't become revenue until the cure finishes, usually four to six weeks for cold process and months for a castile. That is why the cure rack reads your fair calendar: the question is never "when is it ready," it is "which show can it make."
Where do my recipes go?
Nowhere. The calculator runs in your browser, the recipe is kept in local storage on your device, and the export button hands you a CSV or plain-text copy any time. No signup, nothing uploaded. If you sign in to MadeKeeper on this device, the app leaves a copy of your shelf and your next fairs here so the page can answer from them — that copy never leaves the device either.