Shampoo Cost Per Wash
Calculator
Results
- Washes per bottle
- 40
- Cost per wash
- 0.3
- Weeks a bottle lasts
- 10
- Cost per year
- 62.4
Beauty and personal care results
| Washes per bottle | 40 |
| Cost per wash | 0.3 |
| Weeks a bottle lasts | 10 |
| Cost per year | 62.4 |
formula-map diagram
- Washes per bottle
- 40
- Cost per wash
- 0.3
- Weeks a bottle lasts
- 10
- Cost per year
- 62.4
Beauty and personal care relationship
Formula
cost per wash = price ÷ (bottle mL ÷ dose mL)= 40
Note
This is a simplified model: it applies the mixing ratio, dilution, application rate, growth rate or price you enter to plain arithmetic. Mixing figures use the ratio on your own product's label, because developer, powder and colour ratios differ from brand to brand. Dilutions use C1 x V1 = C2 x V2 and the standard conversion of 20 drops per millilitre; real droppers vary with the oil's viscosity and the dropper itself. Sunscreen amounts use the Du Bois body surface area formula with the application rate you enter, and the SPF figure uses the textbook approximation protection time = SPF x unprotected burn time, which is a simplification: sweat, water, towelling, UV index, altitude, reflection and your own skin all shorten it in practice. Hair, nail and hair-removal timings assume a constant linear growth rate, which varies by person, body area, age, season and health. Costs ignore taxes, sales and waste. Always patch test a new product on a small area first and follow the product label and any professional instructions. This is not dermatological, cosmetic or medical advice; see a dermatologist or a qualified professional for anything affecting your skin, scalp or health.
More in Beauty and personal care
See all →Frequently asked questions
How is the cost per wash calculated?+
Cost per wash = bottle price divided by the total number of washes the bottle provides, where the number of washes is estimated from the bottle's total volume divided by your typical amount used per wash.
What amount of shampoo should I assume per wash?+
A common estimate is one to two tablespoons (roughly 10-15 mL) for average-length hair, though this varies significantly with hair length and thickness; longer or thicker hair generally requires more per wash, which reduces the total number of washes a given bottle provides.
Why does a more expensive shampoo sometimes have a lower cost per wash?+
A higher-priced bottle can still be more economical per wash if it is more concentrated or requires less product per use, or simply comes in a larger size, so comparing sticker price alone can be misleading; cost per wash normalizes for these differences.
Does washing frequency affect the cost-per-wash figure itself?+
No, cost per wash is independent of how often you wash your hair, since it is calculated per individual wash; however, your washing frequency determines how quickly you will use up the bottle and therefore how often you incur that per-wash cost.
How can I use this to compare a large bulk bottle against a smaller one?+
Because cost per wash accounts for both price and how many washes each size provides, it lets you fairly compare a large economy bottle against a smaller one even when their total prices are very different, revealing which size actually offers better value over time.