Perfume oil to alcohol ratio, by concentration

A perfume is a concentrate of aromatic materials diluted in alcohol, and the ratio between them is the concentration: an eau de toilette sits around 5 to 15 percent concentrate, an eau de parfum around 15 to 20 percent, an extrait above that. The percentage is one number with one definition, aromatic mass over total mass, and every ratio on this page is that number rearranged.

What percentage of perfume oil goes in each concentration?

The names are conventions, not regulated grades, and every house draws its lines a little differently. The ranges most perfumers work to, by mass:

• Eau de cologne: 2 to 5 percent concentrate, 95 to 98 percent alcohol.
• Eau de toilette: 5 to 15 percent concentrate.
• Eau de parfum: 15 to 20 percent concentrate.
• Extrait de parfum: 20 to 40 percent concentrate.

Two perfumes at the same percentage can still differ hugely in how loud they are, because the concentrate itself can be made of strong or quiet materials. The percentage describes the dilution, not the volume of the smell. Pick the concentration for the character you want: an extrait is closer to the skin and lasts longer, a cologne throws further at first and is gone sooner.

Should the ratio be measured by weight or by volume?

By weight. A bench works on a scale, materials have different densities, and a drop of a thick absolute is not a drop of alcohol. Every percentage in perfumery arithmetic is by mass unless someone says otherwise, and a formula written in millilitres cannot be reproduced. Alcohol is lighter than water, roughly 0.8 grams per millilitre, so a 30 ml bottle holds about 24 grams of finished perfume, not 30. That one conversion is where most bottle arithmetic goes wrong.

How do I calculate the oil and alcohol for a 30 ml bottle?

Decide the concentration, work out the finished mass, and multiply.

1. A 30 ml bottle at 0.8 g/ml holds about 24 g. Make 25 g so there is a little to spare.
2. For an eau de parfum at 18 percent: 25 g multiplied by 0.18 is 4.5 g of concentrate.
3. Alcohol is the remainder: 25 minus 4.5 is 20.5 g of perfumer's ethanol.

The same concentrate at eau de toilette strength, say 10 percent, is 2.5 g of concentrate in 22.5 g of alcohol. Moving between concentrations changes only the alcohol; the concentrate's internal ratios do not move.

The catch is what is already inside the concentrate. If one of its lines was weighed from a dilution, that line brought its own solvent with it, and the concentrate is weaker than the sum of its written lines. Suppose the 4.5 g of concentrate above is made of 2 g of bergamot essential oil, 1.5 g of hedione and 1 g of ethyl maltol weighed from a 10 percent solution. The aromatic mass is 2 plus 1.5 plus 0.1, which is 3.6 g, not 4.5. In the 25 g bottle that is 14.4 percent, an eau de toilette that thought it was an eau de parfum.

Why does the concentration have only one definition?

Because two definitions give two numbers, and the second one is always the wrong one somewhere. The concentration of a finished perfume is total aromatic mass divided by total batch mass, where the numerator is every line corrected for the strength of the bottle it was weighed from, and the denominator is everything on the scale: the neat materials, the solvent that arrived inside the diluted ones, and the alcohol added to finish. Nothing is rounded before the sum. A formula that computes its percentage from written lines instead of corrected ones, or from the concentrate instead of the whole batch, prints a figure the strip will contradict.

This matters beyond the label. Safety limits are stated against the finished product, so a concentration that is 4 points too high on paper can pass a line that should have failed. The dilution arithmetic behind all of this is on the dilution calculator page.

Does the perfume need to rest after mixing?

Yes. Concentrate and alcohol take days to weeks to settle into each other, and the first day's smell is not the finished one. Weigh, cap, date the bottle, and judge it after at least a week; many perfumers wait four. Chill and filter before bottling if the concentrate carries waxes or resins that come out of solution in the cold.

PerfuMate's finishing sheet does this arithmetic on your own formula: give it the target weight and the concentration and it derives the alcohol, corrects every line for the dilution it was weighed from, and prints one concentration figure that the editor, the list and the batch record all agree on. The same arithmetic runs on its own at the batch calculator, free, in the browser.