Bath Bomb Calculator
Scale a bath bomb batch: set how many bombs and grams each, your soda-to-acid ratio and additive percentage, and get baking soda, citric acid and add-in weights. Worked out in your browser.
Baking soda
-
Show the math
From the batch weight we set aside your additives, then split the dry base into soda and acid by your ratio:
total = bombs × grams each
dry = total − additives
baking soda = dry × r ÷ (r + 1)
citric acid = dry ÷ (r + 1)
Keep everything dry until you mold, water sets off the fizz early. Bind with oil or a light witch-hazel spritz, not water. Mind any slip from oils in the tub, and keep fragrance and color within bath-safe limits, especially for sensitive skin and children.
What this does
A bath bomb calculator scales a batch: set how many bombs and grams each, your soda-to-acid ratio and additive percentage, and get the baking soda, citric acid, and add-ins.
How to use it
- Enter bomb count and grams each.
- Set the soda-to-acid ratio.
- Set the additive percentage.
- Read each ingredient weight.
How it works
The classic dry ratio is 2:1 baking soda to citric acid. Keep everything dry until you mold — water sets off the fizz early.
soda = dry × r ÷ (r + 1); acid = dry ÷ (r + 1)
Understanding your result
The classic 2 to 1 baking soda to citric acid ratio gives a good fizz, and the whole point is keeping everything bone dry until you mold, because any stray water, even humidity, sets off the reaction early and leaves you with flat, crumbly bombs. Witch hazel as a binder evaporates without triggering the fizz, unlike water.
Example
Ten 100 g bombs at 2:1 with 10% additives need about 600 g of baking soda.
Last updated .
Frequently asked questions
How is the batch split?
Total is bombs × grams each. We set aside your additives, then split the dry base into soda and acid by your ratio: baking soda = dry × r ÷ (r + 1), citric acid = dry ÷ (r + 1).
What ratio should I use?
The classic dry ratio is 2:1 baking soda to citric acid. Adjust it to tune the fizz.
How do I stop it fizzing early?
Keep everything dry until you mold — water sets off the reaction. Bind with oil or a light witch-hazel spritz, not water.
Do you store anything?
No — every calculation runs locally in your browser.
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