Saturday, March 10, 2012

Question: How do I figure out the volume of a recipe?

Let's say you want to make some conditioner, and you want 4 bottles of 8 ounces (about 240 ml) each. How do we figure it out from a recipe based on percentages or weight?

The short answer is that you make a 100 gram batch of the stuff, figure out the volume of it, then multiply that to get what you want. Or make a ton of it, bottle some for your friends, and keep the rest for yourself. (This is generally what I do!)

The long answer is almost the same in that it's hard to figure out what volume you'll see from a product based on a weighed recipe, and that's thanks to specific gravity. Pure water at 4 Celsius is our baseline for specific gravity and everything else is compared to it. Water weighs 1000 grams per litre - 1 kg per litre - or 1 gram per millilitre. So a teaspoon or 5 ml of water weighs 5 grams. A tablespoon or 15 ml of water weighs 15 grams. A cup of water at 250 ml weighs 250 grams.

If something is listed as being less than 1, it weighs less than water per gram. If something is more than 1, it weighs more than water per gram. If something has a specific gravity of 1.03, it means it weighs 1.03 grams for every 1 millilitre or 1030 grams per litre.

So if we see cetrimonium chloride listed as having a specific gravity of 0.93, we know this means it weighs 0.93 grams per 1 cc or 1 ml (or 930 grams per litre). Liquid Germall Plus has a specific gravity of 1.15 to 1.25. If you want 0.5% in a lotion and add it in volume at 0.5 ml to a 100 ml batch of lotion, you might have 0.575 to 0.625 ml preservative, which is above the 0.5% recommended!

A lot of oils have a specific gravity of 0.91 to about 0.95. So adding 1 cc or 1 ml safflower oil (specific gravity 0.90) would only add 0.9 grams of oil to your lotion. If you're making a 100 ml batch and you're wanting 10% oil in the product, using 10 ml of oil will leave you with 9 grams of oil, not 10. Take this even higher to a 1000 ml or 1 litre batch (multiplying your recipe by 10) and you'll have 90 grams of oil instead of 100! This can throw your emulsification out of whack and will deprive you of 10 grams of lovely oil!

How do we use this information to figure out the volume of our recipes? Figure that something that is loaded with water - this min-maxed toner, for instance - is going to be close to 100 ml for a 100 gram recipe thanks to the high level of water and other liquid ingredients that are close to water and very few powdered ingredients. If you take a look at this leave in conditioner - is going to be close to 100 ml for a 100 gram recipe because most of the ingredients are around the same specific gravity as water. If you take a look at this body butter, you can see there's about 60% stuff that is around the specific gravity of water, and about 40% stuff that isn't. As a rough estimate, when making this product I would guess that a 100 gram batch will get me 60 to 70 grams of product. If I wanted to make a 4 ounce/120 ml jar, I'd make 200 grams of product and accept that I'd have a little left over. (This is why I buy small jars, so there's no waste! They also make awesome stocking stuffers or random gifts!) When you get into trying to figure the volume of anhydrous products, it's really hard to figure out how to translate the weight to volume!

When all is said and done, it is really just simpler to make the product and measure the volume for future reference. Make more than you think you'll need if you're making a big batch for a special occasion and store the extra in your finished products box for future enjoyment.

If you don't have a storage area for all your finished products, get one! It's fantastic to go into the box and find extra shampoo bars, conditioner bars, and everything else that you can use or give to people as gifts or as examples of your awesomeness!

Related posts:
Weight vs. volume


Lise M Andersen said...

Love this post Susan-. It is a great refresher and reminds me again how wonderfully logical the metric system is..

Danuta Kildan said...

1 gram of Germall plus is 18 drops:)

Susan Barclay-Nichols said...

Hi Danuta! Drops from what kind of dropper? A small 1 ml pipette? A large eye dropper? Small eye dropper? 3 ml pipette? A lab pipette? There are just too many things that can drop a liquid and the drops aren't the same size. This is why we use weighted measurements! :-)

Anonymous said...

Hi there,

I currently use "g" on my label and want to have "ml" instead.

I can fit 150ml of a toner I have into the bottle, so that's fine.

I can't fit 150g of a cream cleanser I have, rather about 146g.

Would this mean that the cream cleanser has a specific gravity of less than 1? something like 0.97?

The MSDS says 2-3.00...if that was the case than would that mean that 1ml is = to 2.5g? which it isn't according to what I have done?

Slightly stuck and don't want to under fill etc!

Thanks in advance :o)


Susan Barclay-Nichols said...

Hi Steve. A specific gravity of 2 to 3 seems really high. Table salt is 2.17 and aluminum is 2.7 (Wikipedia)

For the benefit of all my wonderful readers, specific gravity is mass divided by volume or mass/volume. We use kg/l or g/ml to figure this out.

So having 146 grams to 150 ml, means you have about 0.97 specific gravity, which is what you calculated (This does mean it can't be 2 to 3. I'm not sure where they arrived at that number!)

Related posts:
How do I figure out the volume of a recipe? A post all about specific gravity.