Soap Making Calculator

Last updated: March 26, 2026

Use oil weights in this soap making calculator to plan a bar-soap or liquid-soap recipe, then review the NaOH or KOH amount, water as a percent of oils, superfat-adjusted lye, and batch weight before you mix.

Recipe Inputs

Recipe Summary

NaOH to weigh

143 g

Bar soap | Superfat 5% | Water 33% of oils

Pure NaOH: 150.5 g
Water amount: 330 g
Total oils: 1,000 g
Estimated batch weight: 1,473 g

Formula Breakdown & Oil NotesShow details

Input substitution

Current inputs inserted into the formulas

1.Total oils: 3 oil(s) add up to 1,000 g.

2.NaOH before superfat: sum(oil weight x SAP) = 150.5 g.

3.NaOH after 5% superfat: 150.5 g x 0.95 = 143 g.

4.No purity correction is applied for NaOH bar soap mode, so the amount to weigh remains 143 g.

5.Water amount: 1,000 g x 33% = 330 g.

6.Estimated batch weight: oils + lye + water = 1,473 g.

Oil breakdown

Oil shares and recipe notes

Oil	Weight	Share	Pure NaOH
Coconut Oil Bubbles, cleansing, bar hardness	250 g	25%	47.5 g
Olive Oil Mildness, conditioning, stable bar	500 g	50%	67.5 g
Palm Oil Hardness and creamy lather	250 g	25%	35.5 g

Related Calculators

Use Scenarios

Workflow use

Run a soap lye calculator before mixing

When you already know the oil weights, this soap making calculator doubles as a soap lye calculator for NaOH or KOH, water, superfat, and batch weight before starting a batch.

Mode switch

Switch between bar soap and liquid soap

Use the same soap recipe calculator as a cold process soap calculator for bar soap and as a liquid soap calculator for KOH recipes so you can compare how alkali type and purity change the weigh-out.

Recipe planning

Test oil swaps before scaling a recipe

Use the soap recipe calculator to compare a balanced beginner blend against an olive-heavy bar, a more cleansing mix, or a liquid soap paste plan before scaling a mold or cooking a paste.

Formula Explanation

Step 1

Add the oil weights

Total oils = sum of all oil weights

Every later step depends on the total oil mass and on each oil's share of that total, so the calculation starts by summing the recipe weights you entered.

Step 2

Build the pure lye need from SAP values

Pure lye = sum(oil weight x SAP value)

Each oil has its own SAP value, so this soap lye calculator multiplies every oil by its NaOH or KOH coefficient and then sums those contributions into one total.

Step 3

Apply superfat and liquid-soap purity correction

Discounted lye = pure lye x (1 - superfat); liquid KOH to weigh = discounted lye / purity

A soap recipe calculator still has to lower the alkali target for superfat, and liquid soap may need an extra purity correction when your KOH is not fully pure.

Step 4

Add the water amount

Water = total oils x water percentage

In many beginner soap making calculator workflows, water is entered as a percent of oils; this page then adds that value to the lye and oils to estimate the total fresh batch weight.

How to Read the Result

Primary output

Lye to weigh

In this soap making calculator, this is the practical NaOH or KOH amount to weigh for the selected soap mode after the page applies the current recipe assumptions.

Planning output

Water and batch weight

A soap recipe calculator output is most useful when you read water amount as a planning number based on the selected percent of oils, while total batch weight helps with mold size, container choice, or scaling.

Detail review

Oil breakdown and notes

The oil table shows each oil's percentage and pure lye contribution, while the planning notes flag recipe choices that often deserve a second look before you mix.

Example Cases

Worked example

Case 1: Balanced cold-process bar

Inputs

Soap mode: Bar soap
Oils: 250 g coconut, 500 g olive, 250 g palm
Superfat: 5%
Water: 33% of oils
KOH purity: 90%

Computed Results

NaOH to weigh: 143 g
Water amount: 330 g
Total oils: 1,000 g
Estimated batch weight: 1,473 g
Largest oil share: Olive Oil at 50%

Interpretation

This cold process soap calculator baseline uses a straightforward mixed-oil bar recipe with a moderate superfat and a standard water setting. It is useful for seeing a stable reference before experimenting with softer or more cleansing blends.

Decision Hint

Use a baseline like this to compare later oil swaps or superfat changes so you can see exactly what changed in the lye and water amounts.

Worked example

Case 2: Olive-forward conditioning bar

Inputs

Soap mode: Bar soap
Oils: 600 g olive, 200 g coconut, 150 g shea, 50 g castor
Superfat: 7%
Water: 35% of oils
KOH purity: 90%

Computed Results

NaOH to weigh: 134.5 g
Water amount: 350 g
Total oils: 1,000 g
Estimated batch weight: 1,484.5 g
Largest oil share: Olive Oil at 60%

Interpretation

This soap recipe calculator comparison leans more conditioning than the beginner bar, and the slightly higher superfat plus higher water setting usually points toward a milder bar that also deserves more patience during cure.

Decision Hint

When a recipe gets softer on paper, use the calculator result as the starting point and then plan extra cure time instead of trying to force hardness with a lye shortcut.

Worked example

Case 3: Liquid soap KOH paste plan

Inputs

Soap mode: Liquid soap
Oils: 700 g olive, 200 g coconut, 100 g castor
Superfat: 3%
Water: 30% of oils
KOH purity: 90%

Computed Results

KOH to weigh: 219.2 g
Water amount: 300 g
Total oils: 1,000 g
Estimated batch weight: 1,519.2 g
Largest oil share: Olive Oil at 70%

Interpretation

This liquid soap calculator scenario changes the lye line materially because the calculator uses KOH values and then corrects the weigh-out for the selected purity. That makes it meaningfully different from a bar-soap baseline.

Decision Hint

If you are comparing a bar recipe with a liquid soap version, check the purity assumption first so you are not under-ordering or under-weighing your KOH.

Boundary Conditions

This soap making calculator assumes up to five oil lines entered by weight and is meant to verify lye, water, and batch math, not to auto-balance hardness, cleansing, or conditioning targets for you.

Liquid soap mode assumes the KOH purity you enter. Many commercial KOH products are not 100% pure, so leaving the wrong purity in place can materially change the amount you should weigh.

Water here is modeled from total oil weight, so the displayed batch weight is a fresh-mix estimate before cure, evaporation, cook loss, or post-cook dilution.

Advanced formulations that are controlled by lye concentration, masterbatched lye solution, or a separate water-to-lye ratio should be checked with that specific method rather than only this water-percent workflow.

SAP values can vary slightly by reference table and by how a supplier characterizes an oil or butter. If your supplier provides a product-specific SAP value or purity note, use the more specific source.

Always measure by weight, not by volume, and handle lye with proper PPE and ventilation. A correct number on the page does not replace safe handling practice.

Sources & References

Handcrafted Soap & Cosmetic Guild - Lye CalculatorUsed as the main soap-specific reference for lye-calculation workflow, including NaOH vs KOH planning, SAP-range awareness, and the choice between entering oils by amount or by percentage.
Handcrafted Soap & Cosmetic Guild - Lye Safety GuideUsed for soap-making-specific safety framing, including PPE, safe handling, and the practical reminder to add lye to water rather than water to lye.
SoapCalc - Oil List and SAP ValuesUsed for common oil naming and soap-specific SAP-value conventions when mapping oils to NaOH and KOH requirements in the calculator.
SimpleSoapCalcKept as a supplementary explanatory reference after SERP review because it reflects common web-calculator conventions such as superfat, water planning, NaOH vs KOH mode, and liquid-soap purity correction.

Frequently Asked Questions

How do you calculate lye for soap making?

To calculate lye for soap making, list each oil in the recipe, multiply each oil weight by the correct NaOH or KOH SAP value, add those values together, and then reduce the total for your chosen superfat. If you are trying to understand how to calculate lye in soap making without doing the math by hand, a soap lye calculator automates the SAP and superfat steps for the full recipe.

How do you calculate lye and water for soap making?

Start with the lye requirement from the oils and SAP values, then set the water amount using the method your recipe uses. On this page, the soap making calculator calculates water as a percent of total oils, so the workflow is total oils, then lye amount, then superfat adjustment, then water amount, then total batch weight. That gives you both the alkali to weigh and the water to mix for the current soap recipe.

How do you calculate the amount of lye in soap making after changing one oil?

You need to recalculate the whole formula every time you swap an oil, butter, or fat. Even when the total oil weight stays the same, the amount of lye in soap making changes because each oil has its own SAP value. That is why experienced makers run every recipe revision back through a lye calculator before mixing a batch.

How do you calculate water discount in soap making?

Water discount in soap making means using less water than your normal starting formula, not changing the lye needed for saponification. Because this page uses water as a percent of oils, you create a water discount by lowering that water percentage and recalculating the recipe. The lye amount still comes from the oil SAP values and superfat setting; only the water side of the mix changes.

How do you use a lye calculator for soap making?

Choose bar soap or liquid soap, enter the oils and their weights, pick the measurement unit, then set superfat and water. If you are making liquid soap, also enter KOH purity. After you calculate, use the main result to weigh the lye and water, then review the oil breakdown and formula notes to confirm the recipe still matches your plan.

Why does a liquid soap calculator show more KOH than a bar-soap NaOH calculator?

Potassium hydroxide and sodium hydroxide do not use the same SAP numbers, and liquid-soap recipes often also correct for less-than-100% KOH purity. That is why a liquid soap calculator can show a noticeably larger alkali weight than a bar-soap NaOH calculator built from a similar oil blend.

Can I use this soap making calculator for melt-and-pour or rebatch soap?

No. This calculator is for from-scratch lye soap where you are combining oils with NaOH or KOH. Melt-and-pour bases and rebatch soap already went through saponification, so they do not use this lye calculation workflow.