Soap Batch Size Calculator
Turn a bar count and bar weight, or a mould volume, into the oil, water, fragrance and lye weights a soap batch is built from.
At a glance
- What you enter
- Plan from, Bars you want, Weight of one bar, Mould length, Mould width, Mould depth, Superfat, Water as a percentage of oils, Fragrance or essential oil load, Lye solution, as a percentage of the oil weight, Water lost during cure
- What you get
- Total batch weight, Total oil weight, Water weight, Fragrance or essential oil, Total batch weight in grams, Bars this batch fills, Batter weight per bar
- Formula shown
- Yes, every step, right below your results.
- Cost and privacy
- Free, no account needed, and nothing you type is stored.
See worked examples ↓ Read the FAQ ↓ Share this calculator ↓
Results are estimates for general information only, always verify with a professional or official source before acting on them.
How to use the Soap Batch Size Calculator
- 1 Enter Plan from
- 2 Enter Bars you want (bars), Used when planning from a bar count.
- 3 Enter Weight of one bar (oz), A standard bar of cold process soap is about 4 to 4.5 ounces of batter, which cures lighter.
- 4 Enter Mould length (in), Used when planning from a mould. Measure the inside of the mould.
- 5 Enter Mould width (in)
- 6 Enter Mould depth (in), The depth you fill to, not necessarily the full height of the mould.
- 7 Enter Superfat (%), Cold process soap is normally made at 5 to 8 percent. Superfat is the share of oils left unsaponified, so it is set in your lye calculator, not added to the oil weight here.
- 8 Enter Water as a percentage of oils (%), Cold process recipes usually sit between 33 and 38 percent. Check the figure your own recipe and lye calculator call for.
- 9 Enter Fragrance or essential oil load (%), A percentage of the oil weight. The supplier's published usage rate for the specific oil you are using governs, not this figure.
- 10 Enter Lye solution, as a percentage of the oil weight (% of oil weight), The total weight of your lye together with its water, expressed as a percentage of the oil weight. A cold process recipe commonly runs 35 to 40 percent. This is a planning weight only: the real alkali figure comes from a lye calculator, never from this page.
- 11 Enter Water lost during cure (%), Cold process soap cures for four to six weeks and loses water weight. Ten percent is a common planning figure.
- 12 Press Calculate. You get Total batch weight, Total oil weight, Water weight, Fragrance or essential oil, Total batch weight in grams, Bars this batch fills, Batter weight per bar, and every intermediate step stays visible under "How is this calculated?"
- 13 Change one number at a time to see what moves the result, that is usually the most useful thing a calculator can tell you.
Worked examples
Real numbers run through this calculator. Open any example to load it into the form above and change it.
Eight bars at four and a half ounces
A small loaf batch of eight standard bars, worked from the bar count with water at 35 percent.
You enter
- Plan from
- 1
- Bars you want
- 8
- Weight of one bar
- 4.50 oz
- Mould length
- 10 in
- Mould width
- 3.50 in
- Mould depth
- 2.50 in
- Superfat
- 6%
- Water as a percentage of oils
- 35%
- Fragrance or essential oil load
- 6%
- Lye solution, as a percentage of the oil weight
- 38%
- Water lost during cure
- 9%
You get
- Total batch weight
- 36.00 oz
- Total oil weight
- 20.11 oz
- Water weight
- 7.04 oz
- Fragrance or essential oil
- 1.21 oz
- Total batch weight in grams
- 1,020.58 g
- Bars this batch fills
- 8
- Batter weight per bar
- 4.50 oz
Thirty six ounces of batter needs a little over 25 ounces of oils. Buy oil by the pound and allow a little spare.
A ten inch loaf mould
A 10 by 3.5 by 2.5 inch loaf mould, filled to the top, with a lower water figure and a 5 percent superfat.
You enter
- Plan from
- 2
- Bars you want
- 8
- Weight of one bar
- 4.50 oz
- Mould length
- 10 in
- Mould width
- 3.50 in
- Mould depth
- 2.50 in
- Superfat
- 5%
- Water as a percentage of oils
- 33%
- Fragrance or essential oil load
- 3%
- Lye solution, as a percentage of the oil weight
- 38%
- Water lost during cure
- 9%
You get
- Total batch weight
- 35.00 oz
- Total oil weight
- 20.11 oz
- Water weight
- 6.64 oz
- Fragrance or essential oil
- 0.60 oz
- Total batch weight in grams
- 992.23 g
- Bars this batch fills
- 7
- Batter weight per bar
- 5.00 oz
Eighty seven and a half cubic inches, so 35 ounces of batter. At a 4.5 ounce bar that is seven full bars, and the eighth only happens if you cut them a little lighter.
A big market batch
Forty bars at 4.4 ounces, planned as one batch for a market stall.
You enter
- Plan from
- 1
- Bars you want
- 40
- Weight of one bar
- 4.40 oz
- Mould length
- 10 in
- Mould width
- 3.50 in
- Mould depth
- 2.50 in
- Superfat
- 6%
- Water as a percentage of oils
- 35%
- Fragrance or essential oil load
- 6%
- Lye solution, as a percentage of the oil weight
- 38%
- Water lost during cure
- 9%
You get
- Total batch weight
- 176.00 oz
- Total oil weight
- 98.32 oz
- Water weight
- 34.41 oz
- Fragrance or essential oil
- 5.90 oz
- Total batch weight in grams
- 4,989.52 g
- Bars this batch fills
- 40
- Batter weight per bar
- 4.40 oz
A hundred and seventy six ounces of batter. Check the pot, the moulds and the curing space before committing to a batch this size.
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Frequently asked questions
How much oil do I need for a batch of soap?
Why is the oil weight not just the batch weight minus the water?
Does this calculator work out my lye?
Why does my finished bar weigh less than the calculator says?
Which mould dimensions do I enter?
Terms used here
Short, plain-language definitions of the words this calculator uses.