Short answer
Parts per thousand (ppt, or ‰) expresses each material as a share of 1000 parts instead of 100. To convert, divide by 10 for a percentage (25 ppt = 2.5%) and use grams = parts ÷ 1000 × batch size. Perfumers use it because small materials become whole numbers and a full formula sums to a memorable 1000, which makes a missing or duplicated row obvious at a glance.
What a 1000-part formula looks like
An illustrative structure, written the way many perfumers record formulas:
| Material | Parts | Percentage | Grams in 20 g |
|---|---|---|---|
| Hedione | 300 | 30.0% | 6.00 |
| Iso E Super | 220 | 22.0% | 4.40 |
| Bergamot oil | 180 | 18.0% | 3.60 |
| Linalool | 120 | 12.0% | 2.40 |
| Galaxolide 50% | 100 | 10.0% | 2.00 |
| Ambroxan 10% | 50 | 5.0% | 1.00 |
| Vanillin 10% | 25 | 2.5% | 0.50 |
| Aldehyde C-12 MNA 1% | 5 | 0.5% | 0.10 |
| Total | 1000 | 100.0% | 20.00 |
As with any formula, the diluted rows are listed as their solutions. 50 parts of Ambroxan 10% is 5 parts of Ambroxan itself. The perfume dilution and calculations guide explains why that distinction must always be kept.
The conversions
percentage = parts ÷ 10
parts = percentage × 10
grams = parts ÷ 1000 × batch size (g)
At a 1000 g batch, parts are grams. At 100 g, parts divided by 10 are grams. For other sizes, multiply — the full method, with rounding rules, is in how to convert a perfume formula from percentages to grams.
Why perfumers like 1000 parts
- Small materials stay readable. A trace of a powerful material is "3 parts", not "0.3%". Fewer decimals means fewer misplaced decimal points.
- The total is a check. A formula that sums to 1000 is complete; one that sums to 995 has a missing 5 parts somewhere.
- It suits trial-and-error. Adding 10 parts of one material and removing 10 of another keeps the total at 1000, which makes deliberate adjustments easy to read.
Keeping a 1000-part formula exact
When you adjust a formula, the total drifts away from 1000. There are two ways to bring it back:
- Compensate. Every addition is matched by a removal elsewhere. This preserves the total and makes each trial's change explicit, which is the most useful approach while iterating.
- Renormalize. Let the trial total what it totals, then rescale every row by 1000 ÷ new total. A trial totalling 1040 parts is multiplied by 0.9615; each row's share is preserved, and the formula reads in thousandths again.
Here is renormalizing in practice. A trial added 40 parts of linalool to the formula above, making the total 1040:
| Material | Trial parts | × 0.9615 | Rounded to 0.1 |
|---|---|---|---|
| Hedione | 300 | 288.46 | 288.5 |
| Iso E Super | 220 | 211.54 | 211.5 |
| Bergamot oil | 180 | 173.08 | 173.1 |
| Linalool | 160 | 153.85 | 153.8 |
| Galaxolide 50% | 100 | 96.15 | 96.2 |
| Ambroxan 10% | 50 | 48.08 | 48.1 |
| Vanillin 10% | 25 | 24.04 | 24.0 |
| Aldehyde C-12 MNA 1% | 5 | 4.81 | 4.8 |
| Total | 1040 | 1000.01 | 1000.0 |
The linalool went from 12.0% to 15.4% of the formula, and every other material fell by the same proportion — about 3.8% of itself. That second effect is easy to forget: adding one material always dilutes all the others. Compensating instead would have kept the others where they were and taken the 40 parts from one named material.
Renormalizing produces decimals. Round to whole parts only if the formula can tolerate it — rounding a 3-part row to 3 when it should be 2.88 is a 4% change to that material. Many perfumers keep one decimal place for small rows.
Parts per thousand for scaling
Because the total is fixed, scaling a parts formula to any batch is a single multiplication of every row by batch size ÷ 1000. A 250 g batch of the formula above is 0.25 g per part: Hedione 75.00 g, Ambroxan 10% 12.50 g, the aldehyde dilution 1.25 g. For scaling a weighed formula with an arbitrary total, see how to scale a perfume formula.
Don't confuse ppt with ppm
Parts per thousand (‰) is 10⁻³. Parts per million (ppm) is 10⁻⁶ and is used for trace levels — impurities, or regulatory thresholds. The EU labelling threshold for fragrance allergens in leave-on cosmetics, 0.001%, is 10 ppm. Mixing the two up is an error of a factor of a thousand.
Recording a parts formula
Whether you write parts or percentages, the formula record needs the same things: each material with its dilution, the unit, the total, and the batch you actually made. A perfume formula template shows a layout that works for either.
Frequently asked questions
Is ppt the same as per mille?
Yes. Per mille (‰) and parts per thousand are the same unit. In perfumery "ppt" almost always means parts per thousand, not parts per trillion.
Can I mix parts and percentages in one formula?
Don't. Choose one unit per formula and convert everything to it, or every later calculation has to remember which rows are which.
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.