The one thing you aren’t thinking about when shopping for skin care will save you big $$$

There are a lot of factors that go into the skin-care product selection process. First and foremost and by far the most important: the ingredients. Then, maybe, the brand, the price, and the packaging. But one thing you’re probably not thinking about when you’re perusing the shelves for the latest addition to your regimen (at least I know I wasn’t)? The cost per ounce,  AKA how much bang you’re actually getting for your buck.

We had a collective “Aha!” moment in the Well+Good offices this week when Glossier announced that they would be re-launching their Super Serums in new sizes—up to 30 ml from the original 15 ml—without changing the price. So while consumers will still be spending $28 on the product, that $28 will go much farther than it did before because you’ll be able to get more use out of it, and ultimately, replace it less often.

This got us thinking about which products on the market are offering up the best value for your beauty bucks: As in, are all of those $150 serums actually secret steals because of how much you’ll end up getting out of them? To figure it out, start out by dividing the total cost of the product by the number of ounces in the bottle, then take into consideration how much of the product you need to use (peep our guide to that here) and how often you’ll use it (i.e. only in the morning or in the morning and at night). According to cosmetic chemist Ginger King, one pump will push out between .1 and .5 grams of product depending on the packaging, which means you’ll get somewhere between 58 and 283 pumps per ounce.  And my head officially hurts.

To make it a little clearer, here’s an example that completely blew my mind: Biologique Recherche’s cult-fave P50 Lotion has a $116 price tag that would make literally anyone balk. But when you realize that that $116 will get you 8.4 ounces of product, it breaks down to only $13 an ounce. Inexpensive? Not exactly. But when you realize that many of the other brands on the market sell one ounce bottles of their products for well over $100, it suddenly doesn’t seem so bad. I’m not saying we should all run out and drop double hundred dollar bills on a skin-care product (even if it is a really, really good skin-care product), but it definitely does make you think about what, exactly, your money is getting you. Just be sure to bring your calculator the next time you hit the skin-care aisle.

For some seriously affordable products that actually work, here are 10 drugstore diamonds derms don’t go a day without recommending. Plus, why the pros really want you to stop scrubbing your face with walnuts.