Understanding the Toothpaste Calculator
This tool estimates how long a tube of toothpaste will last, how many brushings it provides, and what each brushing (and each day) costs — using the same supply-divided-by-consumption-rate logic you would use for any refillable container. Enter the tube's net weight, how much toothpaste you use per brushing, how often you brush, how many people share the tube, and the tube's price.
The formula
Given a tube weight W (grams), an amount used per brushing A (grams), a brushing frequency F (brushings per day per person), and P people sharing the tube, the calculator applies:
- Brushings per tube: W / A — the total number of times the tube can be used before it is empty.
- Daily consumption: A x F x P — the combined grams used by the household each day.
- Days the tube lasts: W / (A x F x P) — tube weight divided by daily consumption.
- Cost per brushing: tube price / brushings per tube.
- Cost per day: tube price / days the tube lasts (equivalently, daily consumption share of the tube price).
For example, a 100 gram tube used at 1 gram per brushing, twice a day, by one person, provides 100 brushings and lasts 100 / (1 x 2 x 1) = 50 days — about a month and a half.
Where the default amount comes from
Common dental hygiene guidance recommends a "pea-sized" dab of toothpaste per brushing for adults and children over about age 6, which is often estimated at roughly 1 gram (a strip about 2 cm long on a standard brush head). Children ages 3-6 typically need only a pea-sized amount as well, while children under 3 need just a rice-grain-sized smear — a fraction of that weight. Adjust the "toothpaste per brushing" input if you use noticeably more or less than the default.
Why grams instead of milliliters
Most toothpaste packaging states net contents by weight (grams or ounces) rather than volume, since toothpaste is a paste, not a free-flowing liquid. Because its density is close to that of water, using the printed gram weight directly as the tube size keeps the estimate simple and accurate without needing a separate volume-to-weight conversion.
Practical context
This is a planning estimate, not a guarantee — actual brushing habits vary, and a heavier or lighter hand on the tube will shift the real result. Use it to gauge when to reorder, to budget for a household's dental supplies, or to compare the value of different tube sizes and prices per gram.