In short
Pure active is the weight of real fragrance material in a formula, leaving out the solvent its diluted lines carry. To find it, multiply each line's weight by its strength and add them up. It matters because a concentrate is often far from 100% active, so a perfume finished by concentrate weight alone can be noticeably weaker than you think.
What you will learn
- Calculate the active share of a concentrate with diluted lines
- Finish a perfume to a stated active strength
- Explain the difference it makes when solvent is ignored
Before this lesson: Stock Solutions in Practice
A worked formula
| Line | Weight (g) | Strength | Pure active (g) | Solvent (g) |
|---|---|---|---|---|
| A | 6.00 | Neat | 6.00 | 0.00 |
| B | 2.00 | 10% | 0.20 | 1.80 |
| C | 2.00 | 1% | 0.02 | 1.98 |
| Total | 10.00 | 6.22 | 3.78 |
This concentrate weighs 10 g and contains 6.22 g of fragrance material, so its active share is 62.2%. Note what the weight column hides: B and C look equal at 2 g each, yet B has ten times the active.
Finishing to a stated strength
Suppose you want 50 g of perfume with 15% active.
- Active needed: 50 × 0.15 = 7.5 g.
- Concentrate needed: 7.5 ÷ 0.622 = 12.06 g.
- Alcohol to add: 50 − 12.06 = 37.94 g.
Now compare with the naive method, which treats the concentrate as if it were all active. That would weigh 7.5 g of concentrate and 42.5 g of alcohol. It contains 7.5 × 0.622 = 4.67 g of active in 50 g, which is 9.3%, about two-thirds of the strength intended.
Both methods are legitimate conventions if you say which you are using. Some people state a perfume's strength as concentrate weight. The important thing is that your record states which, so that your 15% today means the same as your 15% next year. The guide to calculating concentration deals with bottle sizes and densities.
What about a concentrate that also has solvent as a line?
Some formulas include a solvent such as dipropylene glycol as its own line. It adds weight and no fragrance, so it counts as 0% active. Treat it the same way as carried solvent. That is also why two formulas with the same percentages on paper can be very different in strength.
Three useful percentages
You now have what you need for the distinction the app and many perfumers use:
- Formula share: line weight ÷ total weight. A is 60%, B is 20%, C is 20%.
- Absolute share: line's pure active ÷ total weight. A is 60%, B is 2%, C is 0.2%.
- Relative share: line's pure active ÷ total pure active. A is 96.5%, B is 3.2%, C is 0.3%.
These three answer different questions, and the next study guide practices them. In short, formula share is what you weigh, while the relative share describes the composition of the smell itself.
Practical exercise: Calculate and finish one concentrate
Use an accord of yours with at least one diluted line, or this one: X 3.00 g neat, Y 4.00 g at 10%, Z 3.00 g at 1%. Answer check: total 10.00 g; pure 3.43 g; active share 34.3%.
- Calculate pure active for each line, and the active share.
- Calculate how much concentrate and alcohol you need for 30 g at 15% active.
- Calculate the true strength you would have made with the naive method.
- If you have the materials, make both at small scale, and compare on strips.
- Decide which convention you will use from now on, and write it at the top of your notebook.
You have done this well if your figures tie out (pure + solvent = total), and your notebook now states your convention. For the worked set: 13.12 g of concentrate plus 16.88 g of alcohol.
Common mistakes
- Reading the weight column as the composition. Check the pure column instead.
- Assuming supplier materials are neat. Many musks and strong materials are sold diluted.
- Stating a percentage with no convention. "15%" of what?
Key terms
- Pure active
- The weight of actual fragrance material in a line or formula, leaving out the solvent carried by its dilutions.
- Active share
- The pure active in a concentrate divided by its total weight.
Knowledge check
Written and reviewed by the RUŌOD Lab team. This is general education, not legal, regulatory, medical or safety advice. Example dilutions and exercises are for learning, are not validated products, and have not been safety-assessed. Completing a lesson confers no qualification. How we check these lessons.