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Lotion Calculator
Use this free lotion calculator to build a DIY lotion recipe that actually adds up. Set your batch size and the percentage of water, oils, butter, emulsifier, preservative, and fragrance, and it gives you the grams and ounces of each ingredient, warns you if the percentages do not total 100, and works out the cost per ounce.
500 grams makes about 17.6 ounces — roughly two 8-ounce jars with a little to spare.
Leave the cost at 0 if you do not want a cost per ounce. Add up what you paid for the ingredients in this batch.
| Ingredient | Grams | Ounces |
|---|---|---|
| Water / hydrosol (68%) | 340 g | 11.99 oz |
| Liquid oil (20%) | 100 g | 3.53 oz |
| Butter (5%) | 25 g | 0.88 oz |
| Emulsifier (5%) | 25 g | 0.88 oz |
| Preservative (1%) | 5 g | 0.18 oz |
| Fragrance (1%) | 5 g | 0.18 oz |
| Total | 500 g | 17.64 oz |
How it works
A lotion recipe is a set of percentages that must add up to exactly 100. If they add to 97, you have 3 percent of the batch unaccounted for; if they add to 104, you have more lotion than your jar holds. This calculator keeps the maths straight: you set the batch size and each percentage, and it gives you the weight of every ingredient in grams and ounces.
The water phase is the biggest part of most lotions, usually 60 to 75 percent. It can be plain distilled water, a hydrosol such as rose water, or a mix of the two. The oil phase is next: liquid oils such as sweet almond, jojoba, or sunflower at about 15 to 25 percent, plus a butter such as shea or cocoa at about 3 to 8 percent for a richer feel. Together the oils and butter decide whether the lotion feels light or heavy on the skin.
Ounces = grams ÷ 28.35
Percentages must total 100%
Cost per ounce = batch cost ÷ total ounces
The emulsifier is what holds the water and oil together — without it, the lotion splits into two layers within a day. Common emulsifiers are used at about 4 to 6 percent. The preservative, usually 0.5 to 1 percent, is what keeps a water-based lotion safe from mould and bacteria; a lotion without a preservative must be used within days and kept in the fridge. Fragrance or essential oil is used at 0.5 to 1 percent — more can irritate skin.
Weighing in grams is far more accurate than measuring in cups or spoons, because oils and butters have different densities. A kitchen scale that reads to 0.1 grams is the single most useful tool for lotion making. The calculator shows ounces too, so you can work with either unit, but grams are the safer choice for small batches.
The cost per ounce is optional. Add up what the ingredients for this batch cost you — the oil, butter, emulsifier, preservative, and fragrance — and the calculator divides it by the total ounces. A 500-gram batch costing $12 works out to about $0.68 per ounce, which you can compare with the price of a shop-bought lotion to see what you are saving.
Worked example
You want to make a 500-gram batch of lotion with 68% water, 20% liquid oil, 5% shea butter, 5% emulsifier, 1% preservative, and 1% fragrance, and the ingredients cost $12.
Step 1: Check the percentages — 68 + 20 + 5 + 5 + 1 + 1 = 100%.
Step 2: Work out the grams — water 500 × 68% = 340 g, oil 500 × 20% = 100 g, butter 500 × 5% = 25 g, emulsifier 500 × 5% = 25 g, preservative 500 × 1% = 5 g, fragrance 500 × 1% = 5 g.
Step 3: Convert to ounces — 340 g ÷ 28.35 = 11.99 oz, 100 g = 3.53 oz, 25 g = 0.88 oz, 5 g = 0.18 oz, for a total of 17.64 oz.
Step 4: Cost per ounce — $12 ÷ 17.64 = $0.68 per ounce.
The result is a 500 g batch totalling 100%, with 340 g of water, 100 g of oil, 25 g each of butter and emulsifier, and 5 g each of preservative and fragrance, at $0.68 per ounce. That is exactly what the calculator shows for these inputs.
FAQ
Why must lotion percentages add up to 100%?
Because the percentages describe the whole batch. Each percentage is a share of the total weight, so all the shares together must equal the whole jar. If your percentages add to 97, then 3 percent of the batch is missing; if they add to 104, you have planned more lotion than the batch size. This calculator warns you whenever the total is not 100.
How much water should be in a lotion?
Most lotions are 60 to 75 percent water. More water makes a light, fast-absorbing lotion; less water and more oil makes a richer cream. The default recipe here uses 68 percent water, which suits a light everyday lotion. Use distilled water or a hydrosol, not tap water, to keep the lotion fresh.
Do I need a preservative in homemade lotion?
Yes, for any lotion that contains water. Water-based lotions can grow mould and bacteria within days without a preservative, and you cannot always see or smell the contamination. Use a broad-spectrum preservative at the maker's recommended rate, usually 0.5 to 1 percent, and follow its instructions exactly.
Should I measure lotion ingredients in grams or cups?
Grams. Oils and butters have different densities, so a cup of oil and a cup of butter do not weigh the same, and small amounts such as 1 percent of preservative cannot be measured accurately in spoons. A kitchen scale that reads to 0.1 grams gives repeatable results, so the same recipe works every time.
How much does homemade lotion cost per ounce?
It depends on your ingredients, but a simple 500-gram batch often costs $10 to $15 in materials, which works out to roughly $0.60 to $0.85 per ounce. Enter your own batch cost in the calculator to get your exact figure, and compare it with shop-bought lotions of the same size to see your saving.