How to Use the Phat Sudz Lye Calculator
Step 1 — Your Mold Choose a common mold size from the list (2 lb loaf, 3 lb loaf, 4 lb loaf, or slab) or select Custom and enter your own inner dimensions in inches. Enter your pour height — this is how high you'll actually fill the mold, not the full depth of the mold. Enter your bar slice thickness (1 inch is standard). The calculator will automatically suggest a total oil weight based on your mold volume.
Step 2 — Type of Lye Select NaOH for bar soap. NaOH is what you need any time you're making solid bars. (KOH is for liquid soap only.)
Step 3 — Total Oil Weight This field fills in automatically from Step 1. You can also type your own amount if you already know it. Choose your preferred unit — ounces, pounds, or grams.
Step 4 — Water For beginners, leave this set to % of Oils and use 38%. Experienced soapers sometimes use 32–33% for faster unmolding, but 38% gives you more working time at the bench.
Step 5 — Additional Settings Set your superfat to 5% — this is the safe standard and leaves a little extra oil in your finished bar for skin conditioning. If you're adding fragrance or essential oils, enter the amount in ounces per pound of oils (most fragrance oils run 0.8–1 oz/lb — check your supplier's recommendation). If your recipe includes citric acid, enter it here and the calculator will automatically adjust your lye amount.
Step 6 — Oils, Fats & Butters This is where you build your recipe. Click + Add Oil, select an oil from the list, and enter its percentage of your total oil weight. Keep adding oils until your percentages add up to exactly 100%. The calculator shows your totals as you go so you can see where you are.
Step 7 — Soap Qualities & Fatty Acids This panel updates live as you adjust your recipe. It shows you how your soap will perform — hardness, cleansing, conditioning, lather type, iodine value, and INS. Use these as a guide, not strict rules, but aim to stay within the suggested ranges when you're starting out.
Step 8 — Recipe Summary Once Steps 1–6 are complete, your full recipe appears here: exact lye amount, water amount, total oils, fragrance, and total batter weight. You can add a recipe name and print it directly from this page.
1Your Mold
Start here — pick a common mold or enter your own dimensions. We'll calculate how much oil you need automatically.
Common mold sizesUse your actual pour height, not full mold depth.
How thick you cut each bar. 1 inch is standard.
2Type of Lye
NaOH makes firm bar soap. Use NaOH if you want to make bars.
3Total Oil Weight
← Select your mold in Step 1 and this fills in automatically. Or type your own amount.
4Water
Beginners: use 38%. Experienced soapers often use 32–33% for faster unmolding.
Lye as % of (lye + water). e.g. 33 means lye is 33% of the solution.
Parts water per part lye. e.g. 2 means twice as much water as lye.
5Additional Settings
5% is the safe standard for beginners. Leaves extra oils for conditioning.
Check your supplier's max usage rate. FOs typically 0.8–1 oz/lb; EOs lower.
Extra NaOH is added automatically (citric acid × 0.624).
6Oils, Fats & Butters
Enter each oil as a % of your total oil weight. Percentages must add up to 100%.
| Oil / Fat / Butter | % | oz | lb | g | NaOH SAP | KOH SAP | |
|---|---|---|---|---|---|---|---|
| Totals | 0% | -- | -- | -- | |||
7Soap Qualities & Fatty Acids
Updates live as you build your recipe. These are guidelines — experienced soapers often go outside them intentionally.
| Quality | Range | Your Recipe |
|---|---|---|
| Hardness | 29–54 | -- |
| Cleansing | 12–22 | -- |
| Conditioning | 44–69 | -- |
| Bubbly Lather | 14–46 | -- |
| Creamy Lather | 16–48 | -- |
| Iodine | 41–70 | -- |
| INS | 136–165 | -- |
| Fatty Acid | % | |
|---|---|---|
| Lauric | -- | |
| Myristic | -- | |
| Palmitic | -- | |
| Stearic | -- | |
| Ricinoleic | -- | |
| Oleic | -- | |
| Linoleic | -- | |
| Linolenic | -- | |
| Sat : Unsat | -- |