How to Use the Soap Calculator

Pick NaOH (sodium hydroxide) for a hard bar soap, or KOH (potassium hydroxide) for a liquid or soft soap. This is the first choice to make because it changes the lye amount the calculator works out for every oil in your recipe.

If your KOH is only 90% pure (check the label — most craft-supply KOH is), tick the 90% KOH box once you've selected KOH. It's greyed out for NaOH since purity discounting doesn't apply there.

Want the reasoning behind NaOH vs. KOH? See the FAQ below the calculator.

Choose a unit — pounds, ounces, or grams — then enter the total weight of oils only you want to use. Don't include water, lye, or fragrance here; the calculator adds those separately once you know your oil weight.

Sizing a batch for a specific mold? Two easy ways to estimate the oil weight you'll need:

• Water-fill method: weigh your empty mold, fill it with water, then weigh it again — that water weight is a reasonable stand-in for oil weight (soap batter is close to the same density as water).
• The 0.4 rule: measure your mold's inside length × width × height in inches and multiply them together, then multiply that number by 0.4 to get ounces of oil. For example, a 9 × 12 × 1.25 in mold: 9 × 12 × 1.25 = 135, then 135 × 0.4 = 54 oz of oils.

Pick whichever water method you're most comfortable with — % of oils, lye concentration %, or water : lye ratio — they all describe the same water amount, just measured differently. Changing the dropdown updates the label under it so you always know what number to type.

Not sure where to start? A 30% lye concentration (or roughly a 38% water-as-percent-of-oils) is a common, forgiving default for cold process soap.

For what a lower vs. higher lye concentration actually does to your batter, see the FAQ below the calculator.

Super Fat is the percentage of your oils left un-saponified on purpose — it's what keeps a bar from feeling stripping. 5% is a standard starting point; some recipes run higher for a more conditioning bar.

Fragrance is entered as ounces of fragrance oil per pound of your base oils. Check your fragrance's IFRA usage limit before setting this — the calculator will multiply your rate by your batch size and show the total fragrance weight to measure out.

Type into Jump to oil... to filter the list, or just scroll it. Clicking an oil shows its SAP value and stats in the One column on the left — a quick preview before you commit it to your recipe.

When you've found the oil you want, either click Add to Recipe or double-click it in the list. It appears as a new row in Panel 6 below, ready for a percentage.

Not sure what an oil brings to a recipe? Browse the full Oil Properties Glossary to compare SAP values, fatty acids, and soap-quality stats for every oil in the database without adding anything to a recipe first.

For each oil in your recipe, type a percentage or a weight — editing either one recalculates the other automatically. Use the small + and − buttons next to a row to insert a new row below it or remove it.

Keep an eye on the Total row at the bottom of the table. Your percentages need to add up to 100% before the calculator can generate a recipe summary — if they don't, a message under the table tells you by how much you're off.

While you build, watch the All column back in Panel 5 — it updates live with your blended recipe's soap-quality stats and fatty acid profile, with a coloured dot showing whether each one sits inside its typical range.

Once your oils total 100%, Panel 7 fills in with your full recipe: exact water, lye, oil, and fragrance weights in pounds, ounces, and grams, plus your finished soap-quality stats and fatty acid breakdown.

Give the recipe a name, and jot down any additives or notes you want printed alongside it (colourants, botanicals, cure time, batch info).

• Save Recipe stores it in this browser only (it isn't tied to a customer account), so you can reload it later from the same device.
• Export Recipe (JSON) and Download (.txt) save a copy of the recipe as a file.
• Save as PDF and Print produce a clean, printable recipe card — the two checkboxes above them let you drop the quality charts or print without colour to save ink.

A reminder on lye safety before you get started: see the FAQ below the calculator.