Build a blend from the fats soapers actually use with tallow. Lye is recalculated from the saponification value of every oil you pick, and the batch is sized backward from your mold — or, for liquid hand soap, from the bottles you want to fill.
New to this? Read Safety and Before your first batch before you buy anything, and Soap-making terms, explained when a term stops you. Then the short version: set your mold size, press Best all-around on the Blend tab, weigh what the table says in grams, and follow the method. Leave fragrance and additives out of your first batch.
Everything below fills the mold exactly
Liquid soap uses potassium hydroxide (KOH), not the sodium hydroxide you use for bars. They are different chemicals with different weights — NaOH in this recipe makes a hard lump that will never dissolve. You cook the fats and KOH into a thick paste, then melt that paste into water to make the pump soap. Everything below switches over: the lye, the water, the label, the method and the card. Start from one of the liquid recipes under Fats — bar blends heavy in tallow make a cloudy liquid.
Handmade dish soap is true soap, not detergent. It cuts grease well and rinses clean in soft water, but it won't pile up suds like store dish liquid, and in hard water it leaves a faint film on glasses — a splash of white vinegar in the rinse water clears it. Keep the superfat low: free oil is what leaves dishes greasy.
Percentages of total fat weight — aim for 100%
Recalculated from your blend
Weigh the lye in grams. At this batch size one tenth of an ounce of lye is worth about 1.5 points of superfat. A scale reading whole grams resolves four times finer than one reading 0.1 oz, and costs nothing to use.
Verify before you mix. Run the same blend through SoapCalc or Bramble Berry's calculator and confirm the lye weight agrees within a gram or two. Two independent calculations is the only real check.
Set fragrance weight in Batch, above
Added at light trace, last thing before the pour. Use a soap-safe fragrance or essential oil — candle and diffuser oils are not the same thing and can seize a batch.
Not sure what ceiling to use? See IFRA Category 9 on the Sell tab for how to read your supplier's certificate, and why the percentage basis matters.
Tick an additive and the batch re-solves around it. Each one takes weight out of the fat budget so the mold still fills to the brim, which is why the oil weights shift slightly when you check a box.
Most moisturizing first — the circle rates it 1–10
The goal finder is built for bars — it holds tallow at 40% or more and castor under 8%, which is right for a bar and wrong for a bottle. For liquid hand soap, start from one of the liquid recipes under Fats on the Recipe tab instead.
Pick a goal and the calculator searches every blend it can build under real constraints — castor capped at 8%, lauric oils at 32%, tallow at 40% or more, and the other four properties held in range wherever possible — then loads the winner into Fats on the Recipe tab.
Estimated from fatty acid profiles
Two different meanings of the same words. The bar labelled Cleansing measures one narrow thing: how much of your fat is lauric and myristic acid. It is not a verdict on the finished soap. Superfat, water and cure all change how the soap actually behaves and none of them touch these five bars, because none of them change which fats are in the pot. Read the bars as a description of the recipe, and superfat as the dose.
Reading these. Each number is simply the percentage of your blend made of certain fatty acids — the ones named in monospace under each bar. They are not scores out of 100 and not marks out of ten. Creamy lather at 37 means 37% of your fats are palmitic, stearic and ricinoleic; it doesn't mean the bar got a B. The shaded band is where most soapers aim, and sitting outside it isn't a mistake — a high-cleansing bar is exactly right for shop hands and wrong for a face. Profiles are typical values; real oils vary by crop, region and refining.
Saved recipes, or what's on the bench now
Costs use today's prices from the Cost section on the Sell tab, so two recipes saved months apart are compared fairly. Properties are the same fatty-acid sums as the bars at the top of the page. Saved recipes don't remember the water basis, so both are worked at their saved lye strength.
Start from the pot, not the wish
Why this is the useful direction. If you render your own tallow there is a fixed amount of it and no more, so the honest question isn't how much to buy — it's how far what you have actually goes. This works backward from one fat to the batter it makes, the mold that holds it and the bars you get out. Change the blend and the answer changes with it.
It sizes the mold, not the recipe. Press the button and your mold figure on the Recipe tab is set to the batter this makes. If that's larger than the mold you own, make the batch in two pours or scale the amount down until the number matches.
Every value this calculator uses
Each fat needs a specific weight of lye to saponify, and published values disagree by a few percent because real crops and rendering batches vary. Assuming a value higher than your actual oil overdoses the lye and can leave free alkali in the bar. Assuming one lower only leaves extra fat. So every figure below sits at or near the low end of its published range, checked against SoapCalc, The Soap Kitchen, and the international Codex standards for edible oils and fats (the US Pharmacopeia for castor). Real oils can still come in a little lower, which is why this page never offers less than 5% superfat for bars or 2% for liquid soap, and why the Superfat note under Lye solution on the Recipe tab shows where your batch lands at both ends of the range.
| Fat | Lye per gram | Low – high | Spread |
|---|
Cross-checked against the chemistry. Every value here was also derived independently from each oil's fatty acid make-up, using molecular weights rather than any published chart. Thirteen of the seventeen agree within 3%, which is about as close as this kind of estimate gets. The four that don't, all for known reasons: coconut, palm kernel and babassu carry short-chain acids (caproic, caprylic, capric) that the standard profile leaves out, so the derived figure runs low; shea and rice bran hold several percent unsaponifiable matter that never becomes soap, so their real lye demand sits below the pure-triglyceride estimate; and beeswax is not a triglyceride at all but a wax ester, which is why it takes barely a third of the lye a fat of similar weight would.
For liquid soap, every figure in the table is sodium hydroxide. The page multiplies each one by 1.403 — potassium hydroxide's molecular weight over sodium hydroxide's, 56.106 against 39.997 — then divides by the KOH purity you set, so 90% flakes need about 1.559 times the NaOH figure. The same low-end values carry straight over.
Two to watch. Palm kernel has the widest official range, 0.164 to 0.181. One popular chart lists 0.156, which is below that range and is an error — the same chart’s KOH figure converts to 0.178. The 0.176 used here is the common published value, but it sits about 7% above the official low end, the biggest gap of any fat, so a bar heavy in palm kernel loses the most cushion if a lot comes in low: keep the superfat at 6% or more. Coconut’s published figures disagree more than any other common fat’s; it is used here at the bottom of its official range.
Cold process — pour, then cure
What to have on the bench
Digital scale reading 0.1 g, 2 kg capacity. Stick blender — not a whisk, you'll be there an hour. Two heatproof containers, stainless or HDPE plastic marked #2 or #5. A silicone spatula. An infrared or candy thermometer. Safety goggles that seal, not glasses. Nitrile gloves. Your mold, lined if it's wood.
Lye reacts with aluminum, releases hydrogen gas and ruins both the pot and the soap. That includes foil, aluminum spoons and some cheap stock pots. Stainless steel, heavy plastic, silicone and glass only — and not thin glass, which thermal-shocks.
Weigh everything out and line the mold before the lye goes anywhere near water. Once the batch traces you have minutes, not hours, and hunting for a spatula with thickening batter in the pot is how mistakes happen.
Your first batch should be a plain blend with no fragrance and no additives, so you learn what trace looks like without anything accelerating on you. Fragrance is the single most common cause of a first batch going sideways.
Every fat needs a different amount of alkali to saponify. Coconut takes 0.178 g of lye per gram; beeswax takes 0.069. Swap 10% of a blend from coconut to shea and the lye requirement drops by half a percent — small, but enough to matter at the margins of superfat.
Check it rather than trust the listing. Line it, fill with water to half an inch below the rim, and weigh the water. Soap batter runs within a few percent of water's density, so that number is your capacity. A mold rated by volume instead of weight will read differently.
These weights are wet batter. Bars lose roughly 10–15% of their weight to evaporation over the cure. A 4.6 oz slice comes off the rack near 4 oz — so if you're labeling a net weight for sale, weigh cured bars, not fresh ones.
Calculated against 100% pure NaOH. Certified food-grade lye runs 99%+, and anything less means slightly less alkali than the label says — which lands on the safe side again. Don't substitute drain cleaner; the additives aren't disclosed.
Liquid soap is different: potassium hydroxide is sold at about 90%, the rest being water it holds on to, and this page weighs more of it to make up for that. So set the purity to what your label says. Telling the page 90% when the flakes are really purer overdoses the lye.
It works, and it's a good use for tallow you already have, but palmitic and stearic acid make cloudy potassium soap that can settle into a white layer. Keep tallow to about a quarter of the fats, let the bottles sit for a week or two and pour the clear soap off the top. Beeswax and the butters don't belong in liquid soap at all.
Leaf fat or suet, rendered wet and strained twice through cloth. Any meat or protein left behind goes rancid in the cured bar and shows up as orange spots six months later.
30% coconut cleans hard — right for shop hands and dishes, drying for some people in the shower. Drop it to 20–25% and give the difference to tallow for a gentler bar.
Shea, cocoa and mango butter belong at 5–15%; past that they mute the lather. Castor stays under 8% or the bar turns sticky and soft.
It happens to everyone
Usually a mis-weighed oil or a blender that never reached real trace. Wait 48 hours before judging — tallow bars often firm up late. If it's still soup, the batch can be rebatched: grate it, melt it down with a splash of water in a crock pot, and remold. Nothing is wasted.
Too much lye, too little water, or the batch overheated. A crack down the middle means it got too hot — that bar is still usable. White crystalline pockets are unsaponified lye: wear gloves, and don't use that batch on skin. Rebatching fixes it.
Properly measured soap is safe once cured. If a bar makes your hands feel slippery-slick and tingly after rinsing, or stings, something went wrong — don't use it. Inexpensive pH strips on a wet bar should read about 9 or 10; much above that, rebatch.
Old-timers touch a cured bar to the tongue to check for lye. It works and it's traditional, but as a beginner don't — a genuinely lye-heavy bar will burn you. Use strips, or simply wait the full cure on a batch you weighed carefully.
Milky in the clarity test — not finished, keep cooking. Oily layer after diluting — skim it; next time cook longer or superfat less. Too thick or jelly-like — stir in more hot water, a little at a time. Too thin — stir in a salt solution (1 part salt to 4 parts hot water) a teaspoon at a time; go slowly, because too much turns it cloudy and thin again. Cloudy — usually tallow or other hard fat, and harmless; let it settle and pour off the top.
Trace, superfat, gel phase and the rest
Kept in this browser only
Stored on this device. Saving keeps the whole setup — fats, mold, superfat, water, method, additives and prices. It lives in this browser's storage, so it won't follow you to your phone and it goes away if you clear site data. Print the card for anything you want to keep permanently.
What's on the rack
Yours — printed on the card
These print in the Batch notes box on the card. Leave it empty and that box prints blank with room to write by hand. Notes travel with the recipe when you save it, and stay in this browser between visits.
Everything you'll pour, and what to buy for it
On hand is what's already on your shelf — type it once and it stays in this browser, so the list only asks you to buy the difference. Weights are exact, not rounded to a scale; round up when you buy. Water is listed so you remember the distilled jugs — for liquid soap it includes the dilution water — and packaging counts one wrapper per bar or one pump bottle per bottle.
What you pay per pound, A–Z — saved in this browser
Heaviest first, the way the rule asks
Ordered by weight, heaviest first. Not by the order you added them and not oils-then-everything-else — by what each one actually weighs in the finished bar, which is what the rule asks for. Water is ranked on what is left after the cure, not what went into the jug, and the glycerin the reaction frees is counted and ranked with the rest.
Dish soap has two extra rules. Strong degreasing soap is the kind the CPSC expects to carry an eye warning, so the dish soap label adds “Avoid contact with eyes. Keep out of reach of children.” And California’s Cleaning Product Right to Know Act covers dish soap (not hand soap) sold there, including online orders shipped there: list the ingredients on the label and on a website, and put a toll-free phone number and web address on the label.
Call it soap and nothing else. Plain soap sold as soap is exempt from FDA cosmetic rules. The moment the label claims it moisturizes, soothes, heals or treats anything, it becomes a cosmetic or a drug and the rules change. List ingredients in descending order by weight, give a net weight from cured bars, and put your name and address on it.
Why the odd names. Once lye meets fat there is no tallow or coconut oil left in the bar — there's sodium tallowate and sodium cocoate. Labels naming the raw oils are technically describing something that isn't in the product any more, though plenty of small makers list both.
Listing, market card or social post — soap words only
How it stays soap. The writer builds sentences only from what the bar is, how it was made, how it lathers and how it cleans — never what it does to skin. Your own words go through the same check as the bar name, and so do the hashtags. The same rule covers your website, your signs and any customer review you share: the FDA judges the bar by everything you say about it.
What the certificate from your supplier means
The International Fragrance Association sets a maximum usage level for every fragrance material, and those maximums differ by what the product is and how it touches skin. Bar soap sits in Category 9 — rinse-off products for body and hand, alongside body wash, shampoo, bath bombs and salt scrubs. When your supplier sends an IFRA certificate, the Category 9 column is the only one that governs a bar of soap — and liquid hand soap sits in the same category, measured against the diluted soap in the bottle. Dish soap is the exception: it is a household product, so it reads Category 10A — household care products with mostly hand contact — and that column can be lower or higher than Category 9 for the same fragrance.
It lists maximum percentages by category. Find the Category 9 figure and compare it to what you're using. If it says 8% and you're at 5%, you're fine. If it says 3%, you come down to 3% or you choose a different fragrance. The number is specific to that fragrance and that batch — it is not a general rule you can carry to the next bottle.
Limits drop when a fragrance contains known allergens or sensitisers. Cinnamon, clove, citrus and some florals commonly land between 0.5% and 3%. A low Category 9 number isn't a quality problem with the oil — it's the reason the certificate exists.
Standards are revised periodically; the 51st Amendment was published in June 2023, with existing products expected to comply by 30 October 2025. A certificate names the amendment it was written against, so an old sheet for a fragrance you've had on the shelf for years may predate the current limits.
Not in the United States. IFRA compliance is voluntary here, but it is the industry's standard of care: wholesale buyers ask for it, product liability insurers expect it, and it is the document you would want to hold if a customer ever reacted to a bar.
Go to the source. IFRA keeps a searchable Standards Library that stays current — it carries every published standard with a filter for the amendment, so the link does not go stale when the next one lands. Their Understanding the Standards page explains the categories, including what puts bar soap in Category 9. Neither replaces the certificate for your specific fragrance — that comes from whoever sold it to you.
The measurement trap, and it catches people. IFRA writes its limits as a percentage of the finished product. Soapers habitually think in percentage of oil weight — per pound of oils — and the two are not the same number. A cured bar has lost most of its water, so it weighs appreciably less than the batter you poured, and the fragrance left behind is a larger share of what remains. Set your fragrance against wet batter weight and it quietly concentrates as the bar dries.
So this page shows you both. The Ceiling control under Fragrance & additives on the Recipe tab lets you work in either basis, and the line beside it always reports your fragrance as a percentage of fat weight and as a percentage of the estimated cured bar. Compare that second figure against the Category 9 number on your certificate. Working in fat weight is the more cautious of the two for a normal recipe, which is why it's the default.