Short answer
Perfume concentration is the weight of fragrance concentrate divided by the weight of the finished perfume, times 100. To make a batch at a chosen strength, multiply the batch weight by the concentration to get the concentrate, and make up the rest with alcohol: a 41 g batch at 18% needs 7.38 g of concentrate and 33.62 g of alcohol. Eau de toilette, eau de parfum and extrait are commonly placed at roughly 5–15%, 15–20% and 20–30% or more, but those are industry conventions, not legal definitions.
The formula
concentration (%) = concentrate (g) ÷ finished perfume (g) × 100
If you dissolved 9 g of fragrance concentrate in 41 g of perfumer's alcohol, the finished perfume weighs 50 g and its concentration is 9 ÷ 50 × 100 = 18%. Note the denominator: it is the finished weight, concentrate included, not the weight of the alcohol alone. Dividing by the alcohol (9 ÷ 41 = 22%) is one of the most common mistakes in hobby perfumery, and it overstates the strength.
The calculation is done by weight. If any part of it was measured in milliliters, convert it first — see weighing vs measuring by volume for why, and how.
Working backwards: concentrate and alcohol for a batch
In practice you usually know the batch you want and the strength, and need the two weights:
concentrate (g) = batch weight (g) × concentration ÷ 100
alcohol (g) = batch weight (g) − concentrate (g)
| Bottle | Approx. weight | Concentration | Concentrate | Alcohol |
|---|---|---|---|---|
| 30 ml (1.0 fl oz) | 24.6 g | 15% | 3.69 g | 20.91 g |
| 50 ml (1.7 fl oz) | 41.0 g | 18% | 7.38 g | 33.62 g |
| 100 ml (3.4 fl oz) | 82.0 g | 20% | 16.40 g | 65.60 g |
The 0.82 g/ml figure is an assumption for illustration. A hydroalcoholic perfume's density depends on the alcohol (perfumer's alcohol is commonly around 95% ethanol), any water, and the concentrate itself. Weigh 10 ml of your own finished perfume once and use that number. Fluid-ounce conversions use 1 US fl oz = 29.57 ml and are rounded as bottles are usually labeled.
Making the batch — the order of addition, mixing, resting and filtering — is covered in how to dilute fragrance oil in alcohol.
Typical concentration ranges
The names on perfume bottles describe a strength band, but neither US nor EU law defines them by percentage, and brands use them differently. The ranges below are the commonly cited conventions; you will find sources that shift each band by a few points.
| Name | Typical concentrate | Notes |
|---|---|---|
| Eau de cologne | about 2–5% | Light, often citrus-led; "cologne" in US usage often means any men's fragrance regardless of strength. |
| Eau de toilette (EDT) | about 5–15% | The widest band in practice. |
| Eau de parfum (EDP) | about 15–20% | The most common strength for current launches. |
| Parfum / extrait | about 20–30%+ | Sometimes much higher, sometimes in oil rather than alcohol. |
Two perfumes at the same percentage can smell very different in strength. Concentration measures how much concentrate is present, not how much odor it produces: a concentrate built on powerful, diffusive materials at 10% can project more than a soft one at 20%. Choose a strength by evaluating trials, not from a table.
Which "concentrate" are you counting?
If your concentrate contains diluted ingredients, it also contains solvent. A 10 g concentrate in which 1.35 g is solvent from dilutions holds only 8.65 g of fragrance material. At "18%", the finished perfume then contains 18% concentrate but only 15.57% fragrance material (18 × 0.865).
Both numbers are legitimate. The important thing is to state which one your records mean, and to be consistent between batches. If you change how a material is diluted — from a 10% to a 1% solution, say — a formula specified by concentrate weight will deliver a different amount of that material, while one specified by pure active will not. Formula %, absolute % and relative % explains how to keep these apart.
Changing the strength of an existing perfume
To weaken a finished perfume, add alcohol. To find how much:
new total weight = concentrate (g) ÷ new concentration × 100
50 g at 20% contains 10 g of concentrate. To bring it to 15%: 10 ÷ 15 × 100 = 66.67 g total, so add 16.67 g of alcohol. To strengthen a finished perfume you must add concentrate, which also changes the alcohol fraction — recalculate from the total concentrate rather than adding by eye.
Doing it in software
In RUŌOD Lab a formula's production target takes the batch amount and the concentration you want, and gives the concentrate and alcohol weights, along with the factor by which the formula's rows must be scaled to produce exactly that much concentrate. It is the same arithmetic as above; the benefit is that it is derived from the formula's current total each time, so it cannot drift from the formula after an edit. The perfume dilution and calculations guide shows how these calculations connect.
Frequently asked questions
What concentration should my first perfume be?
Many people start trials around 15–20% for an alcohol-based spray and adjust after evaluating. Make two or three strengths of the same concentrate side by side; it is the fastest way to learn what strength does to a particular formula.
Is perfume oil the same as perfume concentrate?
Often, but not always. "Perfume oil" is sold both as an undiluted concentrate and as a concentrate diluted in a carrier oil. Ask the supplier what the product is, and at what strength, before calculating with it.
Does water count in the concentration?
If you add water to the alcohol, it is part of the finished perfume's weight and belongs in the denominator. It does not count as concentrate. How much water a perfume tolerates, and how to calculate it with the water already in your alcohol, is covered in adding water to perfume.
Written and reviewed by the RUŌOD Lab team. This article is general education about perfume formulation and record-keeping; it is not legal, regulatory or safety advice, and the examples are illustrations, not validated commercial formulas. How we write and check these guides.