The right batch size comes from what you're filling, worked backwards. For candles, weigh how much water a jar holds, multiply by about 0.86 for wax, and split that between wax and fragrance by your fragrance load. For soap, multiply the mold's length, width and fill height in inches by 0.40 to get the ounces of oils, then split them by your recipe's percentages. For lotion, multiply bottles by fluid ounces and convert to grams. Add a small allowance for what's left in the pitcher or pot, and you have a batch that fills exactly what you planned. Below is each worked through, how to handle loss, and a free calculator.
The short version
- Candles: fill per jar = water weight × 0.86; wax = fill ÷ (1 + fragrance load).
- Soap: oils in ounces = mold cubic inches × 0.40; then each oil by percentage.
- Lotion: grams = bottles × fluid ounces × 29.57 (taking lotion as about 1 g per ml).
- Add a loss allowance, often 2% to 5%, for what stays behind.
- Work in weight, not volume, for everything you measure.
- Keep lye and preservative amounts to your calculator and supplier.
- TaroStack scales recipes to the batch you make and takes the right amounts off stock. More below.
Candles: from the jar
Jar holds 10 oz of water
Fill per candle 10 × 0.86 = 8.6 oz of wax and fragrance
Fragrance load 8% of the wax
Wax per candle 8.6 ÷ 1.08 = 7.96 oz
Fragrance 8.6 − 7.96 = 0.64 oz
48 candles, 2% loss allowance
Wax 7.96 × 48 × 1.02 = 389.9 oz (24.4 lb)
Fragrance 0.64 × 48 × 1.02 = 31.2 oz
Wax weighs a little less than the same volume of water, which is where the 0.86 comes from; it's a common rule of thumb, so check it against your wax by weighing one filled jar. Fragrance load is a percentage of the wax weight, and the wax's maker usually says the most it can hold. How to price the finished candle is in how to price homemade candles.
Soap: from the mold
Mold 10 × 3.5 in, filled to 3 in = 105 cubic inches
Oils 105 × 0.40 = 42 oz
Olive 45% 18.9 oz
Coconut 30% 12.6 oz
Shea 20% 8.4 oz
Castor 5% 2.1 oz
The 0.40 ounces of oil per cubic inch is a common starting factor for cold process soap that fills a mold once the lye solution is added; adjust it after your first batch. Lye and water depend on your oils and superfat, so run the recipe through a lye calculator every time, and never scale lye by guesswork. Costing the same recipe per bar is in soap making cost calculator.
Lotion: from the bottles
60 bottles × 4 fl oz = 240 fl oz
240 × 29.57 = 7,097 g, plus 3% loss = 7,310 g
Water 70% 5,117 g
Sunflower oil 12% 877 g
Shea butter 6% 439 g
Emulsifying wax 5% 366 g
Glycerin 3% 219 g
Cetyl alcohol 2% 146 g
Fragrance 1% 73 g
Preservative 1% 73 g
Taking lotion as about 1 gram per milliliter is close enough for planning; weigh a filled bottle to check. Use your own tested formula and your preservative supplier's usage rate, and keep the percentages adding to 100.
Loss: what stays behind
Every batch leaves some behind: wax in the pitcher, soap batter on the spatula, lotion in the mixer and filling machine. Start with 2% for candles, 3% for lotion and soap, then measure: weigh what you made, weigh what you filled, for a few batches. A batch that fills 46 candles instead of 48 is telling you the allowance is too small; one with a jar's worth left over says it's too big. The same scaling logic for food recipes, by weight and by mixer size, is in scaling recipes for production.
Get the calculator
Download the batch size calculator. It has a sheet each for candles, soap and lotion: type the jar, mold or bottle size, how many you want and your percentages, and it works out what to weigh. Soap lye and water are left to your lye calculator, on purpose. It's an ordinary Excel file with no macros, and it works in Google Sheets, LibreOffice and Numbers.
Where this stops working
A calculator sizes one batch. It doesn't know you only have 20 lb of wax left, that the fragrance you need is on order, or that the last three batches filled 46 candles, not 48. And once the batch is made, the wax, fragrance, jars and wicks still have to come off your stock sheet, in the right amounts, by hand.
How TaroStack does it
TaroStack scales the recipe to the batch you make, takes exactly that off stock, and learns from what each batch really filled.
Recipes scale to the batch. A recipe holds its ingredients and its batch size, in the units you use: wax by the pound, fragrance by the ounce, jars and wicks by the each. Units convert for you, so a 50 lb case of wax and a 7.96 oz pour live in the same recipe. "What could I make right now" says how many candles the wax, fragrance, jars and wicks on your shelves can make.
Recording the batch takes it off stock. Record a batch of 48 and TaroStack takes the wax, fragrance, jars and wicks from the lots you used, notes them in the batch record, and puts 48 candles on with their own lot code. Batch record forms carry your own fields, like pour temperature and fragrance load.
And the loss becomes a number. Record what came out good, 46 or 48, and the batch is costed on the good output. Recipe truth, from your own batch history, shows whether a recipe yields what it claims, so a loss allowance that's too small shows up in numbers, not in a short last jar.
| The job | Calculator | In TaroStack |
|---|---|---|
| Size a batch | Type the jar and count | The recipe, scaled to the batch |
| Enough on the shelf? | Go and check | What could I make right now |
| Take it off stock | By hand, later | Recorded with the batch, by lot |
| Is the loss allowance right? | Weigh and guess | Recipe truth from real batches |
Stock, lots and counts are on every plan, from $49 a month; recipes, batches and recipe truth are on Standard at $99. The first 30 days are free, with no credit card. If you'd like a hand setting up, ask, and we'll do it with you.