Most people meet perfumery through the finished bottle. The bench is a different discipline entirely, and it is mostly arithmetic — weights, ratios and the patience to write down what you did. What follows is the small body of maths a formula sheet exists to handle, whether you keep it here or on paper.

Why perfumers weigh rather than count drops

A drop is not a unit. Its size depends on the viscosity of the material, the bore of the pipette and how hard you squeeze — a drop of ethanol and a drop of a thick resinoid can differ several-fold in weight. A formula recorded in drops cannot be reproduced, not even by the person who wrote it.

So everything is weighed, in grams, and a bench scale reading to three decimals is the ordinary tool. Three decimals matters because the most powerful materials in perfumery do their work at fractions of a percent: a few thousandths of a gram of something like a strong aldehyde will change the character of a ten-gram trial completely.

Percentages follow from the weights rather than the other way round. Each material’s weight, divided by the total, times one hundred. The column adds to 100%, and if it does not, something has been mistyped.

What dilution actually means

A material listed at 10% is one part aroma material to nine parts solvent — perfumer’s alcohol usually, or dipropylene glycol where alcohol will not do. Perfumers dilute for two separate reasons, and it is worth keeping them apart.

• To smell it honestly. A great many materials are simply unreadable neat. Undiluted, they arrive as a wall — loud, flat and impossible to judge. At 10% or 1% the same material opens up and shows what it is actually contributing.
• To be able to weigh it. A trace that would weigh 0.002 g neat is below what most bench scales can be trusted to read. At 10% that same trace becomes 0.02 g, which a three-decimal scale handles without complaint.

The consequence is that a sheet has to carry the dilution alongside the weight. Two grams of a material at 10% is two grams of liquid but only 0.2 g of perfume — and if the sheet does not know the difference, the percentage column is describing solvent.

The arithmetic of scaling

A formula is a set of ratios, not a set of weights. To take a trial to a batch, multiply every line by the same factor: the batch weight you want, divided by the total you have. A 10 g trial going to 1,000 g multiplies every weight by one hundred.

The trap is rounding. Round each line independently to a tidy number and the errors accumulate — a fifty-line formula can drift several grams off the batch weight you asked for, and the ratios shift with it. Round the percentages if you want a readable sheet, but let the weights carry their decimals, and reconcile against the total rather than line by line.

Composing bottom-up: the Jean Carles method

Jean Carles taught at Roure and is the reason most formal perfumery training still looks the way it does. His sequence was deliberate, and it inverts what most beginners do instinctively.

• Study one material at a time. On a blotter, followed all the way down over hours and days. You cannot compose with something you do not know, and nearly everything interesting about a material happens long after the first sniff.
• Build a two-material accord. Take two materials across a ladder of proportions — nine to one, eight to two, and so on — and smell them side by side to find the ratio where they stop being two things and become one.
• Treat that accord as a single material and ladder it against a third. This is where a two-note idea starts becoming a composition.
• Build from the bottom up. Base first, then heart, then top. Volatility leaves no choice: what evaporates last has to be settled before anything is laid over it, because the base will still be there long after the top has gone.

If the language of top, heart and base is unfamiliar, we have written it out properly in reading the fragrance pyramid.

Where IFRA fits, and where it does not

The International Fragrance Association publishes usage limits for aroma materials, and the single most misunderstood thing about them is what they apply to. IFRA limits govern the finished product a person wears, not the concentrate on your bench.

The distinction is a multiplication. If your concentrate is dosed at 20% in the finished extrait, a material sitting at 1% of your formula is 0.2% on skin. Reading your bench percentages straight against an IFRA table will tell you that a perfectly compliant formula is five times over the limit.

Concentration is doing real work here in a way that is easy to underestimate — the same concentrate behaves differently at extrait, EDP and EDT strength, which we have covered in what perfume strength actually means.

A calculator is a bench aid, not a certificate. It can flag what it recognises and do the arithmetic; it cannot confirm compliance. Anything you intend to sell needs verification against the IFRA Standards Library and a conformity assessment from your supplier or a qualified safety assessor.

Who this is for

Working perfumers, people partway through a formal course, and the self-taught — which in this craft is most people. The Composer is free, it runs in the browser, and it exists because our own perfumers were keeping formulas in spreadsheets that quietly lost their dilution columns.

If you compose, or want to, the ledger is open. If you would rather start at the other end — smelling before weighing — the sixty-second scent quiz is a better first door.