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 150 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, a prediction of how the bar will behave in the pot, a skin-profile read, a cosmetic ingredient label, and an optional batch cost with a suggested selling price. It works with NaOH, KOH, and dual lye blends, and every recipe can be saved to your account, printed, exported to PDF or YAML, or shared with a link.

Want the full tour of what sets this calculator apart? Read why we built a modern soap and lye calculator, from the safety-first lye math to one-tap recipe sharing.

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. Add additives if you use them. Sugar, salt, and clay each have a type selector, a suggested amount by batch size, and a maximum. They show up on the recipe and on the ingredient label with the right INCI name.
8. Set batch conditions (optional). Your soaping temperature, fragrance behavior, and whether you insulate the mold feed the Batch Behavior card so trace, gel, and overheat predictions match your real setup.
9. Calculate. You get exact lye, water, and oil weights, soap quality scores, a batch behavior read, a skin profile, a cosmetic ingredient label, and (if you have prices set) a batch cost and suggested selling price. From there you can save the recipe to your account, export a PDF or YAML file, print it, copy a shareable link, or log the finished batch to compare predicted vs actual.

Reading the results

After you calculate, the summary predicts how your bar will perform based on the fatty acids in your oils, the additives, and the conditions you set. Treat every prediction as a guide, not a grade. Plenty of good bars sit a little outside the recommended window.

Soap qualities

Six industry-standard numbers, each with a target range shown as a shaded band on the bar. In range is green, close to the edge is yellow, far outside is red.

• 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.

Batch behavior: trace, gel, and overheat

A second card predicts how the pour is likely to go for the temperature, fragrance, and additives you set. Each gauge shows the top drivers pushing it up or down, and a suggestion line calls out concrete adjustments (soap cooler, skip the sugar, do not insulate) when the numbers point that way. A confidence chip near the header tells you how much of your blend has fatty acid data behind the prediction.

• Trace speed. How fast the batch thickens once you combine oils and lye. Slow gives you time for swirls; fast means work quickly.
• Gel tendency. How likely the loaf is to reach a full, even gel phase. Insulating pushes it higher; cool room temperatures push it lower.
• Overheat risk. The chance of a hot spot, crack, or volcano. Sugar, high saturated fats, and insulation all raise it.

Skin profile

A read on how the finished bar sits on skin: cleansing strength, skin feel, and shelf life (rancidity risk). If your blend leans noticeably in one direction (higher cleansing, lower conditioning, and so on) the card notes it. Below those, a small table rates the recipe for sensitive, oily, dry, and normal skin with a short reason for each. It reads from the fatty acid makeup of your oils, so if some of your oils are not yet characterized the card says so instead of guessing.

Ingredient label (INCI)

A cosmetic ingredient list ordered by weight, ready to copy for a label draft. Oils saponify into their sodium (or potassium) salt names, so tallow becomes Sodium Tallowate, coconut becomes Sodium Cocoate, and so on. Superfat oils appear under their botanical INCI names, additives use their proper INCI (Sucrose for sugar, Sodium Chloride for sea salt, Kaolin or Bentonite for the clay you chose), and fragrance shows as Parfum. Use it as a starting point and confirm against your finished recipe and your local labeling rules before you sell.

Batch cost and suggested price

If you set oil prices in the Prices modal, a cost card appears with materials total, cost per bar at your chosen bar weight, and an optional suggested selling price using either a markup or a target profit margin. Lye and fragrance can be included or excluded, currency is configurable, and any oil without a price is listed so the total is never quietly incomplete.

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.

Additives, fragrance, and batch conditions

A tucked-away panel on the left lets you tell the calculator what else is going into the batch and how you are working it. None of these change the lye math (that follows your oils and superfat), but they do change the behavior prediction, the ingredient label, and the recipe sheet.

Additives

Sugar, salt, and clay each have a switch, a type selector (sea vs Dead Sea salt, kaolin vs bentonite vs rhassoul clay, and so on), and an amount box. Leave the amount empty to use a starting suggestion based on your batch size (usually a teaspoon per pound of oils), or enter your own grams. Amounts are validated against a safe maximum and the ingredient label picks the right INCI name automatically. Insulating the mold is included here as a technique switch, not something you weigh.

Fragrance

Enter a fragrance rate as a percent of oils or as ounces per pound. If you want to run more than one scent, open Define Scents to split the total fragrance across a small blend. If you know the behavior of your fragrance (well behaved, accelerating, or floral or spice heavy), set the Fragrance behavior selector so the trace and heat predictions match reality. If you leave it unset, the behavior card carries an explicit caveat instead of pretending.

Batch conditions

Soaping temperature (in F or C) and whether you insulate the mold both feed the behavior engine. Warmer, more concentrated, and insulated blends move faster and hotter. Cooler, more dilute, and open-air blends give you more working time and a milder gel.

Designing a recipe with the Recipe Solver

If you know what you want the bar to be but not which oils to reach for, tap Design a Recipe. Pick your goals (a hard bar, high lather, gentle cleansing, long shelf life, and so on), set optional min or max limits on any oil, and the solver searches your current oil list for mixes that hit those targets. It returns the closest matches, tells you which goals landed in range and which came up short, and adds a "why this works" line for each. If you have set oil prices, you can rank the results by lowest oil cost inside quality bands, so a meaningfully better mix always beats a cheaper one but cost breaks ties. Any result can be pulled straight into the main table with a single tap.

Saving, sharing, and logging batches

My Recipes

Recipes save to your account, not just to the browser, so you can sign in from another device and pick up where you left off. A recipe carries its oils, percentages, superfat, water method, fragrance, additives, batch conditions, and Method & Notes. Notes support light formatting (bold, italics, size levels, lists) and travel with save, load, share, YAML, and print.

Sharing and importing

Share builds a link that reproduces the exact recipe when someone opens it. Export YAML saves the same shape as a plain text file you can archive, email, or feed back through Import YAML later. The two formats are at parity: what goes out comes back the same.

Batch logs

Every time you finish a real batch, tap Log this batch on the behavior card and record what actually happened (trace speed, gel outcome, any overheat). Logs are tied back to the recipe they came from, so you can look at a recipe and see how it has actually behaved for you across pours. Over time, the logs feed calibration work on the behavior engine.

Mold volume scaler

Under the oil weight field there is a small link that opens a mold-volume scaler. Give it your mold shape and dimensions, and it works out how much oil weight to aim for so the batch fills the mold correctly. Handy when you switch molds or want to try a smaller test loaf of an existing recipe.

Frequently asked questions