Velvet Petalia

Makeup expiry tracker & beauty shelf tools

Value, use by use

Cost-per-use calculator for beauty products

Price, pack size and how much you use give the cost of every swipe, pump or drop. Compare up to eight products, and see whether a big bottle will pass its PAO before you finish it.

Your products

Cost per use

Best value: Serum, 100 ml value size at 0.383 per use, even with about 9% left over when its 6-month PAO runs out. That is 0.150 less per use than Serum, 30 ml bottle (28% cheaper).

Cost per use, best value first
ProductUses per packCost per useOne pack lastsSpend per monthPer use, counting PAO waste
Serum, 100 ml value size Best value2000.350about 7 months10.650.3839% past its PAO
Serum, 50 ml bottle1000.460about 3 months14.000.460used within PAO
Serum, 30 ml bottle600.533about 9 weeks16.230.533used within PAO

Cost per use you actually get, best value first

  • Serum, 100 ml value size0.383
  • Serum, 50 ml bottle0.460
  • Serum, 30 ml bottle0.533

Cost per useExtra from the part left when the PAO runs out

Your entries are kept in this browser so they are here next time.

How to work out cost per use

Enter what you paid in any currency; the symbol is only for display, and a decimal comma such as 24,50 works too. Then choose how to count the uses:

  • Pack size and amount per use. Measure one use, for example a pump onto a kitchen scale or into a 5 ml teaspoon. You can mix ml with US fl oz, or g with oz, but not volume with weight, because creams differ in density.
  • Uses per pack, when the pack tells you: 30 sheet masks are 30 uses.
  • How long a pack lasts, the easiest for everyday products: note the day you open one and the day it runs out.

"How often" turns uses into time: how long a pack lasts and what it costs you a month. Add the PAO from the pack and the calculator checks whether you will finish it in time. If not, the leftover is waste, and the last column divides the price by the uses you can actually make before the PAO date.

Worked example: a 30 ml serum costs 32 and you use 0.5 ml each night. That is 60 uses at 0.533 each, lasting about two months. A 100 ml bottle at 70 gives 200 uses at 0.35, but at one a night it would last 200 days, longer than its 6-month PAO of about 183 days. Counting only the 183 uses you get, each costs 0.383: still the cheapest, but less of a bargain than the label suggests.

A month here is 30.44 days (365.25 ÷ 12).

Reading the results

Products are listed best value first, by the cost of each use you actually get. The bar chart shows the same order; a lighter end on a bar is the extra cost of the part you would throw away at the PAO date.

Cost per use is one way to judge value. A product that suits your skin and that you enjoy using is often worth more than a cheaper one that sits in a drawer, and the cheapest pack is no saving if it irritates.

Questions

How do I find out how much I use each time?

Weigh the product on a kitchen scale that reads to 0.1 g, use it as normal for a week, weigh it again and divide the difference by the number of uses. Or count pumps until a pack is empty. If neither is practical, note the day you open a pack and the day it runs out, and use "How long one pack lasts me".

Can I compare a pack in ml with one in grams?

Not directly. A millilitre of cream does not weigh exactly a gram, and the difference depends on the formula. Measure your use in the same kind of unit as the pack, or switch that product to uses per pack or how long it lasts, which work whatever the unit.

Which fluid ounce does the calculator use?

The US fluid ounce, 29.57 ml, which is the one on US labels. The old imperial fluid ounce is 28.41 ml, about 4% smaller. Weight ounces are 28.35 g.

Is the bigger size always better value?

Only if you finish it while it is still good. A larger pack usually costs less per millilitre, but once its period after opening runs out, what is left goes in the bin. Add the PAO and how often you use it, and the last column shows the cost of each use you actually get.

Is anything I type sent anywhere?

No. The sums run in your browser, and your entries are saved only in this browser's local storage so they are still here next time. "Start again" clears them.