Fragrance oil to alcohol ratio: the chart, and the part the chart leaves out
The standard 20:80 oil to alcohol ratio, what it gives you at every bottle size, and the question almost every ratio chart skips: whether those parts are measured by volume or by weight.
Search for a fragrance oil to alcohol ratio and you get the same answer everywhere: 20 parts oil to 80 parts alcohol. It is a reasonable starting point. What almost none of those charts tell you is whether a "part" is a milliliter or a gram, and that single omission is why two people following the same 20:80 ratio end up with two different perfumes.
The standard ratios
Ratios are just concentrations written the other way round. A 20:80 ratio is a 20% concentration; 1:4 is the same thing again. The conventional bands:
| Type | Oil | Ratio (oil : base) | In practice |
|---|---|---|---|
| Eau de cologne | 2-5% | 1 : 49 to 1 : 19 | Splashy, gone in an hour or two. |
| Eau de toilette | 5-15% | 1 : 19 to 1 : 5.7 | Light daily wear. |
| Eau de parfum | 15-20% | 1 : 5.7 to 1 : 4 | The usual target for a home blend. |
| Extrait de parfum | 20-30% | 1 : 4 to 1 : 2.3 | Dense; needs a good composition to carry it. |
| Above 30% | 30%+ | under 1 : 2.3 | Rarely better. Often just harsher. |
What 20:80 actually puts in the bottle
Ratios are abstract until you pour them. For a 100 ml batch, at the densities perfume materials actually have:
| Concentration | Oil (ml) | Oil (g) | Base (ml) | Base (g) |
|---|---|---|---|---|
| 10% | 10 | 9.5 | 90 | 71.1 |
| 15% | 15 | 14.25 | 85 | 67.15 |
| 20% | 20 | 19 | 80 | 63.2 |
| 25% | 25 | 23.75 | 75 | 59.25 |
| 30% | 30 | 28.5 | 70 | 55.3 |
Look at the 20% row. Measured in milliliters the split is 20 to 80, exactly as the ratio promises. Measured on a scale it is not: the oil is heavier than the base, so the same bottle is around 23% oil by weight. Same liquid, two different numbers.
By volume or by weight?
Both methods are legitimate and both are used. They simply are not interchangeable:
- By volume (v/v). You measure with syringes and graduated cylinders. Fast, and what most hobby charts silently assume.
- By weight (w/w). You put the bottle on a scale and tare between components. This is what commercial perfumery and every professional formula sheet means. It is more repeatable, because volume changes with temperature and weight does not.
A formula written as 20% means one thing on a scale and another in a syringe, and the gap widens as concentration rises. If you have ever followed someone's ratio exactly and got a noticeably stronger or weaker result, this is usually why. The mechanics are worked through in volume or weight: why the same 25% gives you two different bottles.
Converting a ratio you were given
Supplier pages quote oil by weight, syringes read in volume, and forum posts mix the two freely. Fragrance oil is taken at 0.95 g/ml and perfumer's alcohol at about 0.79 g/ml, which gives you:
ml = grams / density · grams = ml × density
Alcohol is where this bites hardest: it is roughly a fifth lighter than water, so 100 grams of it is about 127 ml. Weighing out grams when the formula meant milliliters leaves you with far more base than you intended. The full set of conversions is in fragrance oil grams to ml.
Where to start
- 1Blend a 10 ml test at 20%, not a full bottle. Oil is the expensive part and the first attempt is rarely the last.
- 2Let it rest. A fresh blend smells sharp and alcoholic for a few days; maceration is not optional.
- 3Judge it, then move in steps of 2-3 percentage points rather than jumping from 20% to 30%.
- 4Record the ratio, the method (volume or weight), the oil, the batch date and what you thought of it. Without those five, the next batch is a new experiment.
One limit sits above all of this: the IFRA limit for the oil you are using, which is specific to that oil and can be well below 20%. Your supplier's documentation has it. What an IFRA limit is covers how to read it.
Enter a bottle size and a ratio and see the oil and base you need in both grams and milliliters, by volume or by weight.
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