Bath bomb recipe.

Worked example

Six 80 g bombs plus 10% extra is a 528 g batch. At 1% fragrance the dry and oil ingredients scale to: baking soda 274.56 g, citric acid 137.28 g, Epsom salt 52.80 g, cream of tartar 26.40 g, polysorbate 80 10.56 g, butter 21.12 g and fragrance oil 5.28 g. Baking soda is twice the citric acid, 274.56 / 137.28 = 2.

How it works

The formula is the Humblebee & Me Christmas Tree Bath Bombs recipe, in percent of batch weight: 52% baking soda, 26% citric acid, 10% Epsom salt, 5% cream of tartar, 2% polysorbate 80, 4% tucuma butter and 1% fragrance oil. Each ingredient = batch grams x its percent / 100, with the other ingredients scaled down proportionally if you raise the fragrance share. Any skin-safe butter is a substitution you make at your own risk; the source used tucuma butter.

The binder is not weighed. The source mists witch hazel, then a little 70% isopropyl alcohol, until a squeezed handful holds together, and warns that too much liquid makes the bomb react in the bowl instead of in the bath. Its batch of this formula made about ten 2-inch bombs. This tool allows fragrance up to 4%, the top of the Tisserand Institute range for bath products (2 to 4%); the source recipe uses 1%.

Wikipedia describes the fizz as an acid-base reaction between citric acid and sodium bicarbonate that releases carbon dioxide, and lists limonene, linalool and sodium lauryl sulfate as common irritants and allergens found in bath bombs, and says fragrances and dyes are additives that can cause irritation; the citric acid and bicarbonate are diluted in the bath. Humblebee & Me says bombs that contain no water once dry do not need a broad-spectrum preservative.

Sources (opened 2026-10-08): Humblebee & Me, Christmas Tree Bath Bombs; Wikipedia, Bath bomb; Tisserand Institute, Dilution for essential oils (bath products 2 to 4%).

FAQ

What is the baking soda to citric acid ratio for bath bombs?

The published formula this tool scales uses 52% baking soda and 26% citric acid, which is 2 parts baking soda to 1 part citric acid by weight.

How much baking soda do I need for 6 bath bombs?

Six 80 g bombs with 10% extra is a 528 g batch, which at 52% of the formula is 274.56 g of baking soda with 1% fragrance. Change the bomb weight or count to rescale.

How much liquid do I add to bath bombs?

The source does not weigh it. It mists witch hazel, then a little isopropyl alcohol, until a squeezed handful holds together, and stops before the mix starts reacting.

How many bath bombs does a batch make?

The source says its 800 g batch makes about ten 2-inch bombs, so about 80 g each, depending on how many survive molding.

Do bath bombs need a preservative?

Humblebee & Me says bombs that contain no water once dry do not need a broad-spectrum preservative. Do not add water-based ingredients without one.

Can bath bombs irritate skin?

Wikipedia lists limonene, linalool and sodium lauryl sulfate as common irritants, and says fragrances and dyes are additives that can cause irritation. Skip fragrance and colour if your skin is sensitive.