Twelve molds on the counter — how much do you actually mix?
Give it the bomb count and what one weighs, and it works the batch backward — extras carved out at your percent, the rest split soda-to-citric at your ratio, with a little margin for what dusts off. Everything stays in your browser.
The batch
Your ratio & costs
The pack
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 the same batch keeps going after the scale — making it draws the soda, citric, salts, and oils out of inventory by the real grams, and the cost per bomb lands in the price coach that helps you set what to charge. See for bath & body makers 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.
Free tool — no signup
Four questions that come up at the mixing bowl — including the one we deliberately won't answer.
Why is 2:1 baking soda to citric acid a setting instead of baked in?
Because it's a convention, not a constant — 2:1 is the classic starting point, so that's where the calculator starts, but makers run leaner and richer mixes and will defend theirs to the end. Whatever you set, the arithmetic follows: after extras come out, 2:1 puts two-thirds of the remaining mix in soda and one-third in citric, and changing the ratio moves the split with it. Your recipe wins; the default just saves you a tap.
How do I know what one bomb weighs?
Weigh one. A finished bomb from your own mold and your own hands beats any estimate a formula can produce — packing pressure alone swings the number too much. If you haven't poured yet, the sphere assist gives you a starting point from mold diameter: a 6 cm mold works out to about 113 cm³, and at the 1.1 g/cm³ packed-density seed that's roughly 124 g. Treat it as a placeholder — the first bomb you actually weigh replaces it.
How much does it actually tell me to mix?
Count times grams per mold, plus the loss buffer — 12 bombs at 150 g with the 5% default is 1,890 g of mix, not 1,800, because some of every batch ends up dusted across the counter and the mold rims. Your extras percent comes off that total first: at 20% that's 378 g for salts, oils, and colorant, leaving 1,512 g to split at your ratio — 1,008 g of soda and 504 g of citric at 2:1. Add your per-kilo prices and it costs the batch and each bomb the same way.
Can it tell me how much fragrance or colorant to use?
No, and it doesn't try. The calculator splits whatever extras percent you give it into grams — but what any specific oil, fragrance, or colorant belongs at in your recipe is a question for your suppliers' documentation on those exact materials. That's the number worth trusting, so it's the one we won't guess at.