How to Use the SoapCalc Soap Calculator
A step-by-step tutorial. Open the calculator in another tab and follow along.
Before You Start
SoapCalc does one thing and does it well: it takes your oil recipe and calculates exactly how much lye and water you need. Get the lye amount wrong and your soap is either caustic (too much lye) or a greasy mess (not enough). The calculator removes that risk.
You don't need to understand the chemistry to use it. You need a recipe (or an idea of which oils you want to use), and about five minutes.
The calculator is laid out in six numbered sections. Fill them in order, top to bottom. The soap qualities and fatty acid profile update automatically as you work — no need to click a calculate button. When your recipe is ready, click View Recipe Summary at the bottom to see your exact lye and water amounts.
The Six Sections
1. Type of Lye
Pick your lye. Two options:
NaOH (Sodium Hydroxide) — for bar soap. Cold process, hot process, all standard bar soap. This is what most soap makers use.
KOH (Potassium Hydroxide) — for liquid soap. A more advanced process that involves cooking the soap paste and then diluting it with water in a second stage. If you're new, start with NaOH.
If your KOH is 90% pure (most KOH sold for soap making is), check the 90% KOH box. This adjusts the calculation to account for the impurity. If you're not sure about the purity, check the label or ask your supplier.
2. Weight of Oils
Two things here: your unit of measurement and your total oil weight.
Use the dropdown to select Pounds, Ounces, or Grams. This choice affects everything — not just the oil weight, but also how fragrance amounts, lye, water, and all other weights are displayed throughout the calculator and on the Recipe Summary page.
Then enter the combined weight of all the oils in your recipe. Not each oil individually — the total. If you're making a recipe with 10 oz of olive oil, 8 oz of coconut oil, and 6 oz of palm oil, your total is 24 oz.
3. Water
Select your water method from the dropdown. Three options:
Water as % of Oils — The simplest method. If you set it to 38% and your total oils weigh 1 pound, your water will be 0.38 pounds. Beginners: use this method and keep the default 38%. It's safe, it works, and it gives you plenty of time to work with the soap before it thickens. After a few successful batches, you can experiment with reducing to 32–33%.
Lye Concentration — For experienced soap makers who want to set the percentage of lye in the lye-water solution directly. If you want lye to be 34% of the total solution, enter 34.
Water : Lye Ratio — Another way to express the same thing. A 2:1 ratio means twice as much water as lye. Enter 2:1.
All three methods control the same variable — how concentrated your lye solution will be. They're just different ways of expressing it.
4. Additional Settings
Super Fat (%): The percentage of oils that won't react with lye — they'll stay in your soap as moisturizing, unsaponified fat. The recommended default is 5%. It builds in a safety margin (since SAP values are averages, not exact numbers) and gives your soap extra skin conditioning. See the FAQ for more on why 5% is recommended.
Fragrance: Optional. Enter your usage rate and the Fragrance Amount field calculates automatically. Fragrance oils are typically used at about 0.5 oz per pound of oils (roughly 31 g/kg). Essential oils are stronger — usually around 0.3–0.4 oz per pound (19–25 g/kg). The units shown here match whatever you selected in section 2. If you leave fragrance blank, the calculator still works — it just won't include a fragrance amount in the recipe summary.
5. Select Oils, Fats, and Waxes
This is where you browse the oil database and choose your ingredients.
The center of section 5 has the oil list — a scrollable list of 150+ oils, fats, butters, and waxes. Click on any oil and its properties appear in the "One" column on the left: soap qualities (Hardness, Cleansing, Conditioning, Bubbly, Creamy, Iodine, INS) and the fatty acid breakdown (Lauric through Linolenic). The SAP values (KOH and NaOH) are shown below the oil list.
This column lets you compare oils before committing them to your recipe. Click on coconut oil, note the high Hardness and Cleansing. Click on olive oil, notice how Conditioning shoots up and Cleansing drops to zero. This is how you learn what each oil brings to the bar.
To add an oil to your recipe, you have three options:
- Click the oil in the list, then click the Add to Recipe button below the SAP values
- Double-click the oil name in the list
- Click the green + button next to any slot in the Recipe Oil List (section 6) — this adds the currently selected oil into that specific slot
All three do the same thing. Use whichever feels natural.
6. Recipe Oil List
This is your recipe. As you add oils from section 5, they appear here in a table with up to 14 slots. Each row shows the oil name and has fields for % (percentage) and weight.
Enter amounts using one of two approaches:
By percentage (recommended): Enter the percentage of each oil in the % column. Percentages must total 100%. Also make sure you've entered your total oil weight in section 2. This is the most common way to work — it makes scaling recipes easy.
By weight: Enter the actual weight of each oil in the weight column. Don't fill in the total Weight of Oils in section 2 — SoapCalc calculates it from your individual weights.
To remove an oil, click the red − button next to it. To clear everything and start over, click Reset all.
As you enter amounts, the "All" column back in section 5 updates automatically. That column shows the combined soap qualities and fatty acid profile for your entire recipe — not just one oil, but the weighted blend of everything in your recipe list. The Sat : Unsat ratio updates too.
No need to click a "Calculate" button. The numbers update live as you type.
Open the SoapCalc Calculator →
Viewing Your Recipe Summary
When your recipe is ready, click the green View Recipe Summary button at the bottom of section 6. This opens the full recipe page with everything you need to actually make the soap.
The Recipe Summary shows:
- Recipe parameters — total oil weight, water percentage, superfat, lye concentration, water-to-lye ratio, Sat:Unsat ratio, iodine, INS, fragrance ratio and weight
- Exact lye and water amounts — in pounds, ounces, and grams, regardless of which unit you entered the recipe in
- Oil weights — each oil listed with its percentage and weight in all three units
- Soap weight before CP cure or HP cook — total weight of the batch before the water evaporates
- Soap Bar Quality chart — your recipe's values shown against suggested ranges with colored bars so you can see at a glance whether you're inside the guidelines
- Fatty Acid profile — same visual treatment, with bars showing the percentage of each fatty acid
Below those are two text areas: Additives (for notes about colorants, botanicals, clays) and Notes (for cure time, batch date, or anything else you want to remember). Whatever you type here will be included when you print or export.
Recipe Name
At the top of the summary page there's a Recipe Name field. Type a name for your recipe — "First Olive-Coconut Batch," "Lavender Shea v2," whatever makes sense to you. This name appears on the printed recipe.
Printing
Click the Print button at the top right of the summary page. Print it, stick it in a binder, and take it to the kitchen. Most experienced soap makers keep a physical soap notebook — it's faster to flip through paper than scroll through files when you're mid-batch with gloves on.
INCI Names
Click INCI Names to see the International Nomenclature of Cosmetic Ingredients version of your oil list. Useful if you're selling soap and need ingredient labels that comply with cosmetic labeling regulations.
Going Back to Edit
Click Edit Recipe to return to the calculator with your recipe still loaded. Make changes, then view the summary again.
Saving and Loading Recipes
SoapCalc saves recipes as JSON files that you download to your computer. No accounts, no cloud storage, no cookies that disappear when you clear your browser.
To save: On the Recipe Summary page, click Export Recipe. A JSON file downloads to your computer containing your entire recipe — oils, percentages, settings, everything.
To load: On the calculator page, click the Load Recipe button below section 6. Select your saved JSON file. Your recipe, oils, and settings will be restored.
Converting a Recipe to Percentages
Found a recipe online listed in ounces but you want to scale it to a different batch size? SoapCalc can convert it.
- In section 2, select the weight unit the original recipe uses and don't enter a total oil weight yet.
- Add your oils to the recipe list and enter their original weights in the weight column.
- The percentages appear in the % column automatically.
- Note the percentages — they're your recipe in ratio form.
- Now you can change the total oil weight to whatever batch size you want and switch to percentage entry. The proportions stay the same.
One of the most useful tricks if you're adapting recipes from books or forums where batch sizes don't match yours.
Reading the Soap Qualities
The "All" column in section 5 (and the Soap Bar Quality chart on the Recipe Summary page) shows seven numbers for your recipe. Here's what they mean:
- Hardness — How hard the finished bar will be. Higher = harder, longer lasting. Suggested range: 29–54.
- Cleansing — How aggressively the soap strips oils from skin. High cleansing can feel drying. Range: 12–22.
- Conditioning — How moisturizing the bar feels. High conditioning comes from unsaturated fats like olive oil. Range: 44–69.
- Bubbly — Big, fluffy lather. Driven mainly by lauric and ricinoleic acids (coconut oil and castor oil). Range: 14–46.
- Creamy — Dense, stable lather. Driven by palmitic and stearic acids (palm oil, tallow, cocoa butter). Range: 16–48.
- Iodine — Combined iodine value for your recipe. Lower = harder bar. Values above 70 start to get soft. Range: 41–70.
- INS — A composite number from iodine and SAP values. 160 is often cited as "ideal" but it's a rough guideline, not a rule. Range: 136–165.
On the Recipe Summary page, these appear with colored bars against the suggested range. You can see at a glance where your recipe falls. Being outside a range isn't wrong — it just means your soap leans in a particular direction. Some of the best soaps in the world sit outside every one of these ranges.
For a deeper explanation, see the Soap Qualities page.
Reading the Fatty Acid Profile
Below the soap qualities, the "All" column shows the percentage of each fatty acid in your recipe. These are the building blocks that determine how your soap actually performs:
- Lauric & Myristic — Hardness and big bubbly lather. Strong cleansing. Too much = drying.
- Palmitic & Stearic — Hardness and creamy, stable lather. Less cleansing than lauric.
- Ricinoleic — Big lather boost. Only comes from castor oil.
- Oleic — Conditioning and moisturizing. Low lather. The main fatty acid in olive oil.
- Linoleic & Linolenic — Conditioning and a silky feel, but prone to rancidity in high amounts.
The Sat : Unsat ratio gives you a quick read on balance. Around 40:60 is typical, but it varies widely. A coconut-heavy recipe leans saturated. A high-olive recipe leans unsaturated. Neither is wrong.
For a full reference on every fatty acid, see the oil chart.
Safety
Read the lye safety precautions before your first batch. Not after. Lye is caustic and demands respect. Goggles, gloves, long sleeves, ventilation. The equipment page has the full safety gear list.
Technical Notes
SoapCalc requires JavaScript to be enabled in your browser (it is by default on all modern browsers).
SAP numbers are averages compiled from multiple sources: published references, soap making books, and oil/fat databases. Because they're averages, a minimum 5% superfat is recommended to account for natural variation in oil composition.
Iodine values are also averages and serve as general indicators of hardness contribution. Some iodine values in the database are estimated where published data was incomplete.
Want an Oil Added to SoapCalc?
If there's an oil you'd like us to add to the database, send us a request with the following:
- Name of the oil (and alternate names if it has them)
- SAP value (KOH preferred)
- Fatty acid profile: percentages of lauric, linoleic, linolenic, myristic, oleic, palmitic, ricinoleic, stearic
- Iodine value
- INS value (if available — if not, we'll estimate it from iodine and SAP)
- Two or three reliable references for the above data