Catalog SAP: midpoint of a supplier's range. Check the variety and your lot's certificate of analysis. Type numbers without thousands separators; a comma or a period marks decimals.
02
Lye and water
Applied as a lye discount on the oils.
Lye concentration = commercial lye to weigh ÷ (commercial lye + water). Solid lye only; do not enter the purity of a premade solution.
03
Additives and ingredients
Amounts in grams, outside the oil formula. Water content and lye consumption are declared in the ingredient's details.
No additives in this recipe.
04
Fragrance with references
No default usage rate
0 = no fragrance. 1% = 10 g per kg of oils.
Blank = unknown. Zero = do not use.
Of the finished product, fragrance included.
Product category9 · rinse-off products
Does not apply to household cleaning soap or leave-on products.
Enter the certificate and usage guidance for the complete blend. Do not add up the limits of separate fragrances.
Water lost during cure raises the fragrance percentage. The check uses the estimated final weight below and assumes the fragrance is fully retained. A result within the limit you entered does not certify that the product is safe.
05
Batch size and molds
1.05 is an example. Calibrate it with your own fresh soap.
Estimated usable capacity—
Fitting uses the whole fresh soap batch and leaves out the later dilution of liquid soap. Review labor and fixed costs after changing the batch.
06
Yield and costs
100% is a conservative assumption, not a cure forecast.
Added after cure/cook.
Uniform loss; ingredient costs still count.
0 = estimate from final weight. Whole numbers.
Include the percentages that apply to your business.
Price = unit cost ÷ [1 − (margin + fees)/100]. A margin on the selling price is not the same as a markup on cost. Example prices are fictitious.
07
Formula notes
Notes and recipes stay in this browser only. Export them regularly.
My recipe notebook
Local library · versions, comparison and JSON backups.
0 recipes
Your next recipe starts here. Save a formula to start your library.
How to use the SoapDraft lye calculator
Plan the formula, estimate the batch and check the cost before you make soap. The amount of lye depends on the oils you choose, their SAP values, the lye purity and the superfat you enter.
From formula to cost
A workbench for thinking through your recipe.
Start with an example, check your raw materials and fine-tune every detail.
1
Build the oil blend
Add oils by weight or percentage. In percentage mode, bring the total to 100%. Open an oil's details to check its SAP source, or add your own oil using your supplier's certificate of analysis.
Choose NaOH, KOH or dual lye. Enter the purity of the solid lye, the lye discount and the water. Additives that contain water or consume lye need specific data.
Size the batch to your mold, record the fragrance limits and fill in the costs. Save versions, compare recipes and print a sheet listing the assumptions used.
With a SAP value of 190 mg KOH/g, a 5% lye discount, 99% NaOH and a 33% lye concentration, the result is 129.98 g of commercial NaOH and 263.89 g of water. This is a math example with an estimated SAP value, not soap-making instructions.
Frequently asked questions
Saponification, molds and pricing
How do I calculate how much lye I need to make soap?
Multiply the weight of each oil by its SAP value for that lye, add up the results, apply the lye discount and divide by the purity as a decimal. SoapDraft does these steps for you and handles any lye consumption declared for additives separately. Check your ingredient's certificate before weighing.
Do NaOH and KOH use the same amount?
No. Their molar masses differ, and so does the SAP value for each lye. NaOH is used for bar soap; KOH for liquid soap paste. In a dual-lye recipe, the split refers to the chemical equivalents assigned to each lye, not to a division of the weights in grams.
Does a 5% superfat mean 5% oil in the finished bar?
Not necessarily. In this calculator, 5% means reducing the theoretical lye requirement for the oils by 5%. The actual amount of free oil depends on your ingredients and process, and the tool does not measure it.
How much fragrance oil can I put in soap?
There is no universal usage rate. Use the document for the exact fragrance or blend, the rinse-off application and your supplier's guidance. An IFRA limit applies to the finished product. Water lost during cure raises the fragrance percentage, so the fresh soap weight is not enough for this check.
How do I know how much soap fits in my mold?
Measure the inside dimensions or enter the volume in milliliters. Choose a fill level and a measured or estimated density for your fresh soap. The tool calculates the usable capacity and resizes the ingredients proportionally. Density is not the same for every soap.
How do I calculate the price of a bar of soap?
Add up ingredients, packaging, labor and other batch expenses, then divide by the number of sellable units. To include a margin and fees on the selling price, divide that cost by 1 minus the sum of those percentages as a decimal. A $10 cost with a 40% margin and 10% fees gives $20.
Are my recipes public?
No. Your draft, recipes, custom ingredients and history stay in this browser's local storage, with no sign-up and nothing sent to a server. Clearing your browser data can erase them. Export the library as JSON to keep a backup and import it on another device.
Can I make liquid soap with the result?
The KOH calculation gives you the paste ingredients. Water for later dilution is recorded separately and counts toward the final weight and cost. Viscosity, stability, preservation, process and safety assessment must be worked out outside the calculator.
