Example Data Table
| Oil |
Weight |
NaOH SAP |
Water Method |
Superfat |
| Olive Oil |
500 g |
0.134 |
2:1 water to lye |
5% |
| Coconut Oil 76 Degree |
250 g |
0.183 |
2:1 water to lye |
5% |
| Shea Butter |
150 g |
0.128 |
2:1 water to lye |
5% |
| Castor Oil |
100 g |
0.128 |
2:1 water to lye |
5% |
Formula Used
Zero superfat alkali = sum of each oil weight multiplied by its SAP value.
Discounted alkali = zero superfat alkali × (1 − superfat ÷ 100).
Purity adjusted alkali = discounted alkali ÷ (lye purity ÷ 100).
KOH estimate = NaOH alkali × 1.403, before purity adjustment.
Water by ratio = required alkali × water to lye ratio.
Water by concentration = required alkali × ((100 − concentration) ÷ concentration).
Water by oil percent = total oil weight × water percent ÷ 100.
Total batch = oils + alkali + water + fragrance + additives.
How to Use This Calculator
Choose the weight unit first. Select NaOH for bar soap or KOH for liquid soap. Enter the superfat value and lye purity. Pick a water method. Add oil weights for the recipe. Use custom oil fields when your oil is not listed. Press Calculate to see the lye, water, percentage, and batch totals. Use CSV or PDF buttons to save the current batch record.
Understanding a Lye Recipe
A lye calculator helps soap makers balance oils, alkali, and water before a batch is mixed. Each oil needs a different amount of alkali. That need is called the SAP value. The calculator multiplies every oil weight by its SAP value. It then adds the results. The total gives the zero superfat alkali amount. Superfat reduces that amount, so a small portion of oil remains unsaponified. This gives a gentler bar and a useful safety margin.
Why Oil Percentages Matter
Oil percentages show the structure of a recipe. A high coconut oil share can raise cleansing and hardness. Too much may feel drying. Olive oil often adds mildness. Castor oil can support lather. But large amounts may make a sticky bar. The percentage table helps you see the full recipe at a glance. It also makes scaling easier. You can compare a small test batch with a larger mold batch.
Water Planning
Water is not only a filler. It changes mixing speed, trace, cure time, and unmolding. A water to lye ratio is easy to control. A lye concentration method is often preferred by experienced makers. Lower concentration means more water. Higher concentration means less water. The calculator provides both approaches. It also includes water as a percentage of oils for older recipe styles.
Purity and Batch Records
Lye purity affects the real alkali strength. If purity is below one hundred percent, the required weight increases. This tool adjusts for that value. It also records fragrance, additives, total batch weight, and estimated oil statistics. These notes help repeat a successful batch later.
Interpreting Results
Use the results as a planning guide. Confirm the lye type before weighing. Review warnings before mixing. Compare the suggested water amount with your fragrance behavior. Some scents accelerate trace. Slow recipes give more time for swirls, layers, embeds, and labels.
Safe Use
Always measure by weight. Use a digital scale. Wear gloves, sleeves, and eye protection. Add lye to water, never water to lye. Work in a ventilated area. Keep children and pets away. This calculator supports planning, but it cannot replace careful handling. Check every recipe twice. Test new formulas in small batches. Keep written records for every soap attempt.
FAQs
What does this lye calculator do?
It estimates alkali, water, fragrance, additive, and total batch weight from oil weights, SAP values, superfat, purity, and water settings.
Can I use it for NaOH and KOH?
Yes. Choose NaOH for solid bars. Choose KOH for liquid soap. The KOH option uses a common conversion factor.
What is superfat?
Superfat is the oil portion left beyond the alkali reaction. It adds a safety margin and can change the finished soap feel.
Why does lye purity matter?
Impure lye has less active alkali by weight. The calculator increases the required amount when purity is below one hundred percent.
Which water method should I choose?
Beginners often use a water to lye ratio. Experienced makers may prefer lye concentration for better control over trace and cure.
Can I add oils not listed?
Yes. Use the custom oil fields. Enter a name, weight, and reliable NaOH SAP value from your supplier or reference.
Is the PDF a batch record?
Yes. The PDF summarizes the main result and oil breakdown. The CSV provides spreadsheet-friendly details for recipe records.
Does this replace safety checks?
No. Always verify SAP values, measure carefully, wear protection, and check the recipe twice before mixing any lye solution.