Soap Batch Calculator: Mold Size to Oils, Recipe Percent to Grams

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Opens on the book's Market Batch. Change any number to your own and press Calculate.

Start from fills the boxes below

Mold measured in

The mold, inside

Length

Width

Height to where you fill

Or water to the fill line g, for an odd shape

Oil per mL g; the metric rule

Oil per in³ oz; the inch rule

Oils you will use g; blank = the 0.70 rule's figure

Your scale reads to

The recipe, as % of the oils

Oil 1

Oil 2

Oil 3

Oil 4

Oil 5

Oil 6

Enter the mold and press Calculate.

The formula

Mold volume = length × width × height (mm × mm × mm ÷ 1000 = mL; in³ × 16.387 = mL), or the water it holds
Oils = 0.70 g per mL, or 0.40 oz per in³: less than the volume, because the batter also holds lye and water
Each oil = its % × the total oils ÷ 100, then rounded to what your scale can read
The percents must add to 100

The book's worked example, Chapter 2. The book's 10-inch loaf mold is 254 × 85.725 × 63.5 mm inside = 1,382.66 mL (84.375 in³). The 0.70 rule gives 967.86 g; the 0.40 rule 956.8 g. The book rounds down to 960 g and splits it olive 40 % = 384 g, coconut 25 % = 240 g, shea butter 20 % = 192 g, high-oleic sunflower 10 % = 96 g, castor 5 % = 48 g.

Weigh everything, oils included: a cup of olive oil and a cup of coconut oil do not weigh the same. Tare the container first. Prices are illustrative US supplier prices from October 2026, shown without a currency sign; put in your own. Everything stays in your browser: no sign-up, nothing stored.