Beauty Calculators
Shampoo cost per wash.
Find out how many washes you get from a bottle, how many weeks it lasts and what each wash costs, for shampoo and conditioner together. Measure your real dose for an honest answer. Runs in your browser.
Your products
What it costs
Fill the form and press Calculate.
Worked example
A 250 ml shampoo at $10, using 10 ml a wash and washing 3 times a week. 250 / 10 = 25 washes, so the bottle lasts 25 / 3 = 8.3 weeks and each wash costs $10 / 25 = $0.40. A year of 156 washes is $62.40. Add a 250 ml conditioner at $12 using 15 ml a wash: 16.7 washes, $0.72 a wash, and together $1.12 per wash or $174.72 a year.
How it works
washes per bottle = bottle ml / dose ml. cost per wash = price / washes per bottle. weeks a bottle lasts = washes per bottle / washes per week. per month = cost per wash x washes per week x 52 / 12; per year = cost per wash x washes per week x 52. Price per 100 ml lets you compare bottles of different sizes.
The dose is the unknown that matters most: a bottle gives twice as many washes at 5 ml as at 10 ml. Squeeze what you normally use into a measuring spoon once to see it. Washing less often lowers the yearly cost without changing the bottle price, so try different washes-per-week values.
Sources and basis (checked 2026-10-05): arithmetic on the figures you enter; no dose is assumed. Spoon sizes are standard approximations: 1 teaspoon about 5 ml, 1 tablespoon about 15 ml.
FAQ
How long does a bottle of shampoo last?
Bottle ml divided by the ml per wash gives the washes, and washes divided by washes per week gives the weeks. A 250 ml bottle at 10 ml per wash and 3 washes a week lasts about 8 weeks.
How much shampoo should I use per wash?
Many people use about a teaspoon to a tablespoon (5 to 15 ml), depending on hair length and thickness. Measure yours once to get a real dose.
How do I compare shampoo bottles of different sizes?
Use price per 100 ml, shown for each product, or better, cost per wash, since a stronger product might need a smaller dose.
How much does shampoo cost per year?
Cost per wash x washes per week x 52. At $0.40 a wash and 3 washes a week that is $62.40 a year.
Does the calculator include conditioner?
Yes, if you fill in the conditioner bottle. It adds the conditioner cost per wash to the shampoo cost per wash.