Soap Mold Volume & Weight Calculator for Irregular Shaped Molds (Water Method) by Wixy Soap
Not all soap molds are neat squares, rectangles, or tubes — many are beautifully irregular, handcrafted, or uniquely shaped, making it tricky to calculate volume with measurements alone. That’s where the Water Method comes in. It’s a simple, reliable, and time-tested way to determine exactly how much soap batter your mold will hold, no math formulas required.
Irregular Mold Calculator (Water Method)
Fill your mold with water, pour into a measuring cup, and enter the fluid ounces below.
Typical cold process soap batter: 1.05–1.10
Notes
- Use Room-Temperature Water - Measure with plain water at room temperature. Hot or cold water can slightly affect volume due to expansion/contraction, but room temp keeps it simple and accurate.
- Fill to Your Normal Pour Line - Fill the mold exactly to the level you would fill with soap batter (including any headspace you like to leave). Don’t overfill or underfill — this directly impacts your batch size.
This gives you a starting point. After getting the estimated oils (e.g., 8.64 oz → round to 8.7–9 oz), enter that total oil weight into your lye calculator along with your recipe percentages. The lye calculator will then give you exact lye and water amounts.