Perfume is measured in weight, not volume

Essential oils are a completely different chemical composition from carrier oils. Without getting at all technical here, carrier oils are basically vegetable fats that are liquid at normal temperatures, and essential oils are way more complex, and happen to be stuck with the name "oil" while not being what we'd think of as oily. "Essential" is from the French, and means that they are the essence of the plant, not that you can't live without them. ( As in "OMG it's absolutely essential!")

So when a formula is submitted for approval, or for someone to manufacture, it needs to be weighed in grams, and usually rationalised to add up to 100 (as a percentage) or 1000 (by the kilogram).

Also, not all essential oils weigh the same. If you buy a litre of orange oil, it weighs less than a litre of sandalwood. Then drop sizes can be different. When it comes to putting in the alcohol to make your finished fragrance, one litre only weighs around 770g.

If you’ve ever tried to put a kilogram of alcohol into a litre jug, you'll soon find out that it won't fit. 50g of your finished fragrance won't go in a 50ml bottle.

One of our clients who launched a natural perfume wanted to know how to comply with cosmetics regulations. I thought we'd covered most of it, until she told me that she had measured her formula in drops. This needed some work before it could be sent to the cosmetics chemists to have its safety assessment done because the industry works by weight.

Recalculating our client's formula was not that difficult, but we needed to weigh each material, while counting the drops, and rewrite the formula in grams. She had been making 10ml at a time, and that was too small for drops to be a reliable measure. We made 100g.