Water discount calculator
Lye concentration, water-to-lye ratio and water as a percentage of oils — the three ways soapers quote the same thing, converted between each other. Type into any one and the rest restate your batch.
INPUTS
Your lye weight
g
%
OilShare
%
%
%
%
That blend needs 142.9g of sodium hydroxide at 5% superfat. Change the recipe on the lye calculator if you need to add or drop an oil.
The same water, four ways
g
%
: 1
%
Type into any one of the four and the other three restate the same batch. Concentration is the one worth thinking in: it describes the lye solution itself, so it means the same thing whatever size you scale to. "38% of oils" is the old full-water rule and lands on a different concentration for every recipe.
A steeper discount means a hotter, more concentrated solution — above about 40% the lye struggles to dissolve and the jug gets fiercely hot. Always lye into water, never water into lye, and never chase a discount so far that you are adding crystals to a solution that will not take them.
RESULTS
Water to weigh out
290.1 g
33.0% solution 2.03:1 29% of oils
Lye solution, total
432.9 g
Discounted off full water
24%
What the same lye takes at each setting
| Setting | Solution | Water |
|---|---|---|
| Full water | 25% | 428.6 g |
| Light discount | 28% | 367.4 g |
| Standard | 33% | 290.1 g |
| Firm discount | 35% | 265.3 g |
| Heavy discount | 40% | 214.3 g |
The working default. Unmoulds in a day or two and still gives time to swirl.
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How this is worked out
Lye and water are two independent decisions, and only one of them is chemistry. The lye weight comes from your oils; the water is yours to choose, and it changes how the batch handles rather than what it becomes. The trouble is that the craft describes that choice three ways at once. Lye concentration is the share of the solution that is lye. The water-to-lye ratio is the same thing as a proportion. Water as a percentage of oils ignores the solution entirely and measures against the recipe instead — which is why the same "38%" gives a different solution strength for every recipe you apply it to. Here, water weight is the value actually stored, and the other three fields are views of it, so they cannot fall out of step.
lye concentration = lye ÷ (lye + water) × 100
water : lye = water ÷ lye
water % of oils = water ÷ oils × 100
water = lye × (1 − concentration) ÷ concentration
Questions makers ask
What is a water discount?
Using less water than the old "full water" rule of 38% of the oil weight. On a 1 kg batch that rule gives 380 g of water, which works out to a 27% lye solution. Most soapers now work at 33% instead — 290 g of water on the same batch, or about a 24% discount. Less water means a firmer bar sooner and a shorter cure.
Why do recipes quote water three different ways?
History, mostly. "Percentage of oils" is the oldest and the least useful, because it lands on a different lye concentration for every recipe. "Water to lye ratio" came next and at least describes the solution. "Lye concentration" is the one worth thinking in: it says what the solution actually is, so it means the same thing at any batch size. This calculator holds all three in step so a recipe stops being ambiguous.
What lye concentration should I use?
33% is the working default and suits almost everything. Go lower — nearer 25% — when you want a slow trace for an intricate swirl and do not mind waiting to unmould. Go higher, up to about 40%, when you want a firm bar out quickly and are working with a plain recipe. The available settings here are 25% full water, 28% light discount, 33% standard, 35% firm discount, 40% heavy discount.
Does the water change how much lye I need?
No, and this is the thing worth holding onto. Lye is decided entirely by your oils and your superfat. Water only decides how the batch behaves — how fast it traces, how soon it unmoulds, how long it cures. You can change the water discount on a recipe freely without touching the lye weight.
How steep a discount is too steep?
Above about 40% the lye starts struggling to dissolve, the jug gets fiercely hot, and the batter can seize before you have poured it — especially with a fragrance that accelerates. On the example batch, 40% means only 214 g of water. There is little to gain past that point and a real risk of losing a batch to it.
Can I discount water in hot process too?
You want the opposite. Hot process cooks water off, and a batch calculated dry will not spoon into the mould. Most hot process recipes run wetter than cold process ones for exactly that reason — the hot process calculator opens at the wetter default.
Is a 2:1 water to lye ratio the same as a 33% solution?
Nearly, and the small gap is why the two conventions cause arguments. A 2:1 ratio is two parts water to one part lye, so lye is one third of the solution — 33.3%. The standard batch above runs at 2.03:1, which is 33%, or 29% of the oil weight. Three numbers, one batch.
Read before your next batch
- How to use a soap calculator What every field means, where the number comes from, and how to tell when a result is wrong before you have mixed anything.
- What is superfat in soap making? The oil left deliberately unsaponified in a bar — what it is for, what each setting changes, and why the number matters more as a safety margin than as a skin treatment.
- Cold process vs hot process soap Same oils, same lye, two very different afternoons — and one difference that decides it for most people.
- Water discounts explained Lye concentration, water-to-lye ratio and per cent of oils are three names for one decision — and the decision has nothing to do with how much lye you need.