Tallow Soap Recipe & Lye Calculator

What this soap calculator does

Soap is made by mixing fats with lye. When you combine oils with sodium hydroxide (NaOH, for solid bars) or potassium hydroxide (KOH, for liquid and soft soap), they react and turn into soap. That reaction is called saponification.

Every oil needs a specific amount of lye to convert fully. That amount is the oil’s SAP value, short for saponification value. Use too much lye and you get a harsh bar with leftover caustic in it. Use too little and you get a soft, greasy bar that can spoil. There is no safe way to guess, because changing one oil or one percentage changes how much lye the whole recipe needs.

This calculator runs that math for you. Pick from more than 100 oils, fats, butters, and waxes, set up your batch the way you want it, and it returns the exact lye and water weights to measure out, plus a prediction of how the bar will perform. It works with NaOH, KOH, and dual lye blends, and you can save, print, export, or share any recipe you build.

How to use it

1. Set your total oil weight. This is the combined weight of all your fats, not the whole batch. Pick ounces, pounds, or grams with the display buttons.
2. Add your oils. Choose each oil and give it a percentage of the total. The percentages should add up to 100%. The tracker bar shows your running total and how much you still need to add.
3. Choose a superfat. This leaves a small amount of oil unconverted for a gentler bar. Most makers use 3 to 8%, and 5% is a safe default.
4. Set your water. Define it as a percent of your oils, as a lye concentration, or as a water to lye ratio. The live readout shows all three at once and warns you if your concentration moves into an unsafe range.
5. Pick your lye type. Use NaOH for solid bars, KOH for liquid or soft soap, or a blend of both. If your KOH is the common 90% pure flake, check the “KOH is 90%” box so the weights come out right.
6. Add fragrance if you want it. Enter a rate as a percent of oils or as ounces per pound. Use Define Scents to split a fragrance blend across more than one scent.
7. Calculate. You get exact lye, water, and oil weights along with a set of quality scores. From there you can save the recipe to your account, export a PDF or YAML file, print it, or copy a shareable link.

Reading the soap quality numbers

After you calculate, the summary predicts how your bar will perform based on the fatty acids in your oils. Treat these as guides, not grades. Plenty of good bars sit a little outside the recommended window. Here is what each one means.

• Hardness. How firm and long lasting the bar is. Too high can crack, too low stays soft and dissolves fast.
• Cleansing. How strongly the soap lifts oils off your skin. Higher feels more squeaky, but too high can be drying.
• Conditioning. How soft and moisturized the bar leaves your skin.
• Bubbly. Big, fluffy, airy lather, the kind coconut oil and castor give.
• Creamy. Dense, low, lotion like lather, the kind you get from tallow, lard, and butters.
• Iodine and INS. Two summary numbers that estimate overall hardness and longevity from the whole blend. Use them as a sanity check on the rest.

Superfat, water, and lye: the three dials

Most of how a bar feels comes down to three settings, and you can adjust each one on its own.

Superfat

Superfat, sometimes called a lye discount, is the share of your oils left unconverted on purpose. More superfat means a gentler, more conditioning bar and a bigger safety margin against leftover lye. Go too high and the bar turns soft and short lived. 5% suits most recipes. Rich, oil heavy bars often run 6 to 8%.

Water

Water does not stay in the finished bar. It carries the lye, gets the reaction going, then evaporates during cure. More water gives you a thinner mix and more working time but a longer cure. Less water sets up faster and harder. A lye concentration of about 28 to 40% covers most cold process soap, which is why the calculator flags anything above 40%.

Lye type

NaOH makes solid bars. KOH makes liquid and soft soaps. A dual lye blend lets you fine tune texture, since a little KOH can soften a bar that would otherwise be very hard. Consumer grade KOH is usually around 90% pure, so check that box when it applies and the calculator scales the weight up for you.

Making tallow soap

Tallow is what Blnded Bliss is built on, so this is the part we know best. Rendered beef tallow makes a hard, long lasting, mild bar with a dense, creamy lather. Its fatty acids are close to what skin already produces, which is part of why old fashioned tallow soap feels so gentle. It also puts a byproduct of meat to good use instead of relying on imported palm oil.

How much tallow?

You can make a 100% tallow bar, and it will be hard and gentle, but on its own tallow can feel a little waxy and short on bubbles. Most makers blend it. A common starting point is about 70% tallow with 30% other oils. Coconut oil adds cleansing and fluffy lather, and a small amount of castor oil, around 5%, boosts bubbles. Run a few versions through the calculator and watch the quality numbers move before you commit to a batch.

Superfat and working temperature

Tallow soap usually runs a 5 to 8% superfat, and a pure tallow bar often sits at the higher end. One thing to plan for is that tallow has a high melting point, roughly 95 to 105°F. Melt it fully and soap a little warmer than you would with softer oils, or it can start to set up on you before you are ready.

Swapping fats and curing

Beef, sheep, deer, and goat tallow are close substitutes for each other. Just recalculate the lye whenever you swap, since each one has its own SAP value. Lard behaves much the same but gives a slightly softer, even creamier bar. However you blend it, cure your bars for 4 to 6 weeks, since longer makes them harder and milder, and start with fresh, clean tallow so you do not get the orange spots that come from rancidity later on.

Frequently asked questions