About
Making one of something is easy. Making it again — the same size, the same strength, at a cost you can predict and a price that pays you — is where the guessing starts.
Batch Calculator is a set of free calculators for that arithmetic. Candles, soap, bath bombs, perfume and resin: five crafts that all come down to getting a ratio right before you commit the materials.
What you can work out
- Candles — wax weight, fragrance load, wick sizing, vessel fill, cost per candle
- Soap — lye and superfat, water discount, resizing a recipe, bar yield, cost per bar
- Bath bombs — citric to bicarbonate ratio, mould fill weight, binder and butter percentages
- Perfume — accord percentages, the top/heart/base split, dilution, alcohol ratios
- Resin — volume by shape and depth, the resin-to-hardener split, and the pour depth ceiling
Every tool is on the calculators page.
Where the numbers come from
Every figure on this site — inside a calculator, in a guide table, in a range band — is computed at build time from one reference database. Nothing is typed into prose by hand.
That is a deliberate architectural choice, not a boast. It means a guide can never quietly contradict the calculator it links to, and correcting a value corrects it everywhere at once.
Where we quote someone else’s published figures — a manufacturer’s maximum fragrance load, a supplier’s saponification value — they live in their own table, credited with a link to that party’s own site and stamped with the date we read them. Those are the only hardcoded numbers anywhere on the site.
What the site does not do
- No account. There is nothing to sign up for.
- Nothing is saved. The calculators run entirely in your browser. Numbers you type are never sent anywhere, so there is nothing for us to store, log or lose.
- No email wall on a calculator. If a page offers a printable in exchange for an email, that is a clearly marked, separate choice — the tool above it works either way.
Safety comes before arithmetic
Several of these crafts involve materials that can hurt you. Sodium hydroxide burns. Hot wax burns. Fragrance and essential oils have skin-safety limits set by the people who make them.
A calculator on this site tells you what a ratio works out to. It does not tell you that a ratio is safe for your skin, your materials or your jurisdiction. Always check the safety data sheet and the maximum usage rate published by the supplier of the material actually in front of you, and test small before you scale.
Money
The calculators are free and stay free. The site is paid for by printable worksheets in the shop and by affiliate links, both of which are disclosed — see the affiliate disclosure.
Nothing in a calculation changes because of a commercial relationship. The maths does not know who is paying.
Contact
Corrections are genuinely useful, especially the ones that come with the numbers you entered — get in touch.