Shampoo Bottle Lifespan Calculator

Shampoo Bottle Lifespan Calculator: Time Your Next Purchase

Shampoo usage varies a lot from person to person depending on hair length and thickness, which makes "how long will this bottle last" hard to guess. This calculator estimates it directly from bottle size and your actual usage per wash.

The Formula

Weeks Lasting = Bottle Volume / (Amount per Wash × Washes per Week)

Worked Example

A 400 ml bottle, using 10 ml per wash, washing 4 times a week.

Weeks Lasting = 400 / (10 × 4) = 10 weeks

How to Use This Calculator

1. Enter the shampoo bottle volume in ml.
2. Enter roughly how much you use per wash in ml.
3. Enter your washes per week.
4. Click Calculate to see how many weeks the bottle will last.

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Pair with the Soap Bar Lifespan Calculator for a complete shower supply schedule.