Scale a perfume formula

Take a formula written in drops, parts or millilitres and restate every material in grams at the bottle you actually want — and see how far it really is from the split it claims.

INPUTS
How most published hobby formulae are written, and the least repeatable.
The formula, exactly as it is written
MaterialDrops
drops
drops
drops
100.0 drops in total
Remake it as
ml
Measured in
Written in drops this formula reads as 30/50/20, but by weight it is actually 28/49/23 — a gap of 3 points. The weight figure is the real one, and it is what a professional formula would state.
Drop counts are an estimate, not a measurement — 20 drops to the millilitre is an average, and a thin citrus oil genuinely gives more drops per millilitre than a resinoid does. The weights below are the best conversion available from what the recipe states; weighing your own next batch is what makes it repeatable.
A formula is only as repeatable as the way it was written down. Record yours as percentages of the compound by weight and it will scale to any bottle forever — recorded as "twelve drops of this" it is locked to one afternoon and one pipette.
RESULTS
This formula, by weight
27.7/49.1/23.2
as written: 30.0/50.0/20.0 3.2 points out
Weigh out
MaterialShareAmount
Bergamot27.7%1.247 g
Ylang ylang49.1%2.206 g
Vanilla absolute23.2%1.044 g
Perfumers alcohol (SDA 40B)82.0%20.484 g
Compound
4.5 g
Finished volume
30.0 ml
Every row is converted to a weight using its own density, then restated as a share of the compound — which is why a formula written in drops can come out several points from the split it claims. The share column is the formula you should write down: it fits any bottle, and it is what a professional formula would state.

How this is worked out

A formula printed as drops is locked to the pipette it was written with, and one printed in millilitres is locked to nothing useful at all — because the materials in it have different densities. Both convert to shares of the compound BY WEIGHT, which is the only form that scales: each row's amount becomes a weight using that material's own specific gravity, and the weight becomes a share of the total. Everything derived from the formula — the alcohol, the strength, the note split — is then recalculated from the new bottle rather than scaled alongside it, so editing one row cannot leave a stale figure somewhere else. The reason this is a tool rather than a footnote is the drift: bergamot is 0.876 g/ml and vanilla absolute is 1.1, about 26% apart, so the worked example above claims 30.0/50.0/20.0 and is really 27.7/49.1/23.2. A formula written in parts or grams drifts by exactly zero.

weight = amount × density ml → g, or drops ÷ 20 → ml → g
share = weight ÷ Σ weights
new = share × new compound weight
compound and alcohol are then recomputed from the target bottle and strength

Questions makers ask

How do I scale a perfume formula to a different bottle size?
Convert every row to a share of the compound by weight, then multiply those shares by the new compound weight. The awkward part is the conversion: if the formula is in drops or millilitres, each row needs its own material density, because a millilitre of vanilla absolute weighs about 26% more than a millilitre of bergamot.
Why does my formula show a different note split than it says?
Because it was written in a volume unit. The example above states 30.0/50.0/20.0 in drops and is actually 27.7/49.1/23.2 by weight — 3.2 points out. The weight figure is the real one, and it is what every professional formula states. A formula written in parts or grams shows no drift at all, which is the argument for writing them that way.
How many drops are in a millilitre?
About 20, and treat that as an average rather than a measurement. Drop size follows surface tension and viscosity, so a thin citrus oil gives noticeably more drops per millilitre than a resinoid does. Drops are fine for finding a blend you like and poor for repeating it — which is what this tool is for.
Can I scale a formula written in parts?
Yes, and it is the easiest case. Parts and percentages are already proportional to weight, which is what the author meant, so nothing has to be converted and the note split comes out exactly as written. If you are recording your own formulae, record them this way.
Does the strength change when I scale a formula?
It does not have to, and here it does not. The compound is scaled to the new bottle and the alcohol is recalculated from the strength you pick, so you can take a formula you liked as an eau de toilette and remake it as an eau de parfum without touching a single row.
How should I write my own formulae down?
As percentages of the compound, by weight, adding to 100. A formula recorded that way scales to any bottle forever and can be handed to someone else. The same formula recorded as "twelve drops of this" is locked to one afternoon and one pipette.

Read before your next batch

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