How this calculator works
A tube holds a fixed volume. Subtracting a wastage allowance leaves the amount that actually reaches a brush, and dividing by the amount used per brushing gives the number of brushings in the tube. Dividing by the number of people and their daily brushing routine gives how many days the tube lasts, and dividing the price by those days gives a cost per day. A pea-sized amount is roughly a quarter of a millilitre, the usual guidance for an adult, though children need less and a full brush-length strip is closer to two peas.
Formula
Usable toothpaste = tube volume x (1 - wastage). Toothpaste per brushing = pea-sized amounts x millilitres per pea. Brushings per tube = usable / per brushing. Days = brushings / (brushings per person per day x people). Cost per day = price / days. Annual cost = cost per day x 365.
Worked example
A 75 mL tube with 10 percent wastage leaves 67.5 mL. One pea of 0.25 mL per brushing gives 270 brushings. One person brushing twice a day uses the tube over 135 days, so a 4 tube costs about 0.03 a day and about 10.81 a year.
Advertisement
Frequently asked questions
How much toothpaste should an adult use?
A pea-sized amount is the usual guidance for adults, and the same for children aged three to six, while younger children need only a smear. Using more does not improve cleaning and makes the tube run out faster. Check NHS or dental association guidance for your situation.
Why include a wastage figure?
Real tubes are not used perfectly. Some paste stays in the tube, some is rinsed away, and children often use more than they need. A ten percent allowance is a reasonable starting point; set it to zero for a theoretical maximum or higher for a wasteful household.
Does sharing a tube change the cost?
It spreads the same tube across more brushings, so the tube lasts fewer days but the cost per brushing stays the same. The cost per day rises with the number of people because more toothpaste is used. The annual cost reflects the whole household, not one person.
Is fluoride toothpaste different?
The volume arithmetic is the same. What differs is the concentration and how much is recommended for children of different ages, which is clinical guidance rather than a cost calculation. Follow your dentist or public health guidance for the amount and type of toothpaste.