How to Dilute Fragrance Oil in Alcohol: Ratios and Method

Before you start: what you are diluting

"Fragrance oil" covers several different products, and the arithmetic depends on which you have:

• Your own concentrate — the formula you weighed. You know exactly what is in it, including any solvent that came with diluted ingredients.
• A purchased fragrance oil — usually an undiluted compound, but some are pre-diluted in a carrier such as dipropylene glycol (DPG). The supplier's documents should say. Check the supplier's IFRA certificate for the maximum level allowed in your product category before deciding a strength (see IFRA certificates of conformity).
• An oil-based perfume diluted in a carrier oil rather than alcohol. It cannot simply be mixed into alcohol; many carrier oils are not soluble in ethanol.

Step 1: calculate the weights

Work by weight. The full method and typical strengths are in how to calculate perfume concentration; the short version:

concentrate (g) = batch (g) × concentration ÷ 100
alcohol (g) = batch (g) − concentrate (g)

If you are filling bottles sold by volume, convert milliliters to grams using your finished perfume's density, which you can measure by weighing a known volume. Weighing vs measuring by volume explains why this matters and how much difference it makes.

Make a little more than you need. Some liquid stays on the walls of the vessel and in the filter, and a bottle that is short by a milliliter looks underfilled.

Step 2: choose the alcohol

Most alcohol-based perfumes use ethanol of high strength, often sold to perfumers as "perfumer's alcohol". In the US, ethanol for cosmetic use is usually denatured — made undrinkable with an approved additive — under rules administered by the Alcohol and Tobacco Tax and Trade Bureau (TTB). Different denaturants have different odors and suit different products, so ask your supplier which formula you are buying and whether it is intended for fragrance. Do not use rubbing alcohol (isopropyl alcohol): its own odor is strong and it changes how the perfume smells and evaporates.

Some perfumers add a small amount of distilled water to the alcohol to soften the opening; others add none. If you use water, add it last and in small steps, because too much will cloud the perfume as less-soluble materials come out of solution.

Grades, denaturants and what to ask a supplier are covered in what perfumer's alcohol is. For a perfume in a carrier oil instead of alcohol, see oil-based perfume concentration.

Step 3: weigh and mix

1. Tare a clean, dry glass beaker or bottle on the balance.
2. Weigh in the concentrate. Write down the actual weight, not the target.
3. Add the alcohol, still on the balance, until you reach the batch total. Pour slowly near the end.
4. Close and mix gently by swirling or inverting. The solution should be clear.
5. Label the vessel immediately: formula name and version, concentration, date, batch code.

Adding concentrate first, then alcohol, makes the concentrate weight exact and lets you correct the total with the cheaper component. If the target is a round concentrate weight instead, reverse the order.

Step 4: rest, chill and filter

Freshly mixed perfume often smells rough and may change over the following days and weeks as the components interact. Many perfumers let it rest (macerate) before judging it; how long, and what is actually happening, is covered in perfume maceration and aging. Some materials are only partly soluble in alcohol and appear as a haze later. Chilling the perfume for a day or two and then filtering through laboratory filter paper removes much of what would otherwise drop out in the bottle.

Step 5: record the batch

A finished batch is only repeatable if you can see later exactly what went into it. The minimum record:

• formula name, code and version of the concentrate;
• target and actual weights of concentrate and alcohol;
• concentration, and whether it counts dilution solvent as concentrate;
• the alcohol: supplier, grade or denaturant, lot;
• date mixed, rest period, filtering done;
• observations: color, clarity, smell at mixing and after resting.

The perfume batch record article has a full layout for production batches. The arithmetic behind all of this — including what happens when the concentrate contains diluted materials — is collected in the perfume dilution and calculations guide.

Common problems

The perfume turned cloudy

Usually a solubility problem: too much water, a material that dissolves poorly in ethanol, a carrier oil in the concentrate, or simply cold. Warm a sample to room temperature first; if it clears, chill and filter the batch. If it does not, check the concentrate's components and any water you added.

It smells weaker than the concentrate suggested

Check the arithmetic first — dividing by the alcohol instead of the finished weight, or measuring alcohol by volume, both produce a weaker perfume than intended. Then allow time to rest; a perfume judged on the day it is mixed is not finished.

It smells of alcohol

Some ethanol odor at the first spray is normal. A persistent sharp or chemical odor suggests the denaturant or the alcohol grade; compare a blotter of your alcohol alone with another supplier's.

Frequently asked questions

What ratio of fragrance oil to alcohol should I use?

Ratios hide the denominator, so we suggest thinking in concentration instead. "1 part oil to 4 parts alcohol" is 20% concentrate, not 25%. A common starting range for a spray perfume is 15–20% by weight, adjusted after evaluating trials.

Can I use vodka?

Drinking spirits are typically around 40% alcohol, far too much water for most fragrance concentrates, and the result will cloud and separate. Use alcohol sold for perfumery.