A worked example you can check
The maker’s own store sells OLAPLEX No.4 Bond Maintenance Strengthening Shampoo at $34.00 for 250 mL (checked October 13, 2026). OLAPLEX bases its count of uses on an average of 2.5 mL each time. So 250 mL ÷ 2.5 mL = 100 uses, and $34.00 ÷ 100 = $0.34 a use. At two washes a week, one bottle lasts about 50 weeks: $0.34 × 2 × 52 ÷ 12 = $2.95 a month.
2.5 mL is the maker’s own average, not an amount we measured, and two washes a week is only an example. Most makers don’t say how much to use, so for other bottles you enter your own amount.
Measure once, compare more fairly
Use the amount you actually apply. If you shampoo twice, add both applications when you want the cost of a complete wash. For a mask used every other wash, enter the number of times you use that mask each week.
A pump or spray is not a fixed unit. Measure your usual set of pumps in mL, or weigh the amount in grams, before entering it here. Choose the matching bottle unit.
Keep weight and volume separate
US fluid ounces and mL measure volume. Net-weight ounces and grams measure weight. This calculator converts within the same measurement type, but never turns an 8 oz jar into 8 fl oz. That would require knowing the product’s density.
Formula: cost per use = price × amount per use ÷ bottle amount. Full uses are rounded down; a partial amount left in the bottle doesn’t count as another use.