How long will your collection last?

Worked example

Five bottles with 50, 100, 30, 75 and 50 ml left hold 305 ml. Wearing perfume 5 times a week at 3 sprays of 0.1 ml uses 5 x 3 x 0.1 = 1.5 ml a week, or 78.3 ml a year. 305 / 1.5 = 203 weeks, which is 3.9 years of wearing. With a 3-year keep time you would use 1.5 x 52.18 x 3 = 234.8 ml, leaving about 70 ml past it.

How it works

ml per week = wears per week x sprays x ml per spray. Weeks to finish = total ml / ml per week, years = weeks / 52.1775. ml used in your keep time = ml per week x 52.1775 x keep years, capped at the total. This treats the collection as one pool, which assumes you rotate evenly.

What this is not. People do not rotate evenly: a favourite empties while others sit. The result is a ceiling on how fast the collection can disappear, not a promise. The keep time is your own choice, not a published expiry date.

Sources and basis: pure arithmetic on the numbers you enter; no published figure is used, and any default marked as an assumption or rule of thumb is not a published standard.

FAQ

How long will it take to finish my perfume collection?

Total ml left divided by your ml a week. With 305 ml and 1.5 ml a week it is 203 weeks, about 3.9 years.

How much perfume does a person use in a year?

It depends entirely on habit. At 5 wears a week, 3 sprays and 0.1 ml a spray it is about 78 ml a year. Enter your own numbers above.

What is a good keep time for an open bottle?

There is no published standard. Three years is a common rule of thumb and the default here; change it to what you are comfortable with.

How do I measure ml per spray?

Weigh the bottle, spray a set number of times, weigh again and divide the loss by the spray count and the density. The sprays-per-bottle calculator does this for you.