Toothpaste Usage & Cost Calculator

This calculator follows a step-by-step logic to help you estimate how long your toothpaste will last and how much it costs you over time. Here’s a full breakdown of the process:

1. Daily Usage (Base Consumption)

This is the starting point—how much toothpaste your household consumes per day.

Formula:

Daily Usage = Pea-size × Brushes per person × Number of people

A standard “pea-size” of toothpaste is about 0.25 ml

If each person brushes twice a day, they use 0.5 ml/day

Multiply that by the number of people using the toothpaste

Example:

Let’s say:

Pea-size = 0.25 ml

2 brushes per person

3 people in the household

Then:
0.25 × 2 × 3 = 1.5 ml of toothpaste used per day

2. Adjust for Wastage

Not all toothpaste gets used — some gets stuck in the tube, especially near the end. This step accounts for that loss.

Formula:

Adjusted Daily Usage = Daily Usage ÷ (1 – Wastage%)

If wastage is 5%, you’re only using 95% of the tube’s content. So, you need to divide your usage by 0.95 to know the real rate.

Example:

Daily usage = 1.5 ml
Wastage = 5% (or 0.05)
Adjusted = 1.5 ÷ (1 – 0.05) = 1.5 ÷ 0.95 ≈ 1.58 ml/day

This means you effectively “consume” 1.58 ml/day from the toothpaste due to unavoidable wastage.

3. Durability

Now that we know how much toothpaste is effectively used each day, we can calculate how many days the entire tube will last.

Formula:

Durability (in days) = Toothpaste Capacity ÷ Adjusted Daily Usage

Example:

Toothpaste Capacity = 100 ml
Adjusted Usage = 1.58 ml/day
Durability = 100 ÷ 1.58 ≈ 63.29 days

So, your toothpaste will last for about 63 days before you need a new one.

4. Total Cost Per Time Unit

This is where you translate the durability into real cost per chosen time unit (like per month, per week, etc.). You’re essentially calculating how much the toothpaste “costs” you per period.

Formula:

Cost per unit = Price ÷ (Durability ÷ Unit factor)

Where:

Price = how much you paid for the toothpaste

Durability = how long it lasts (in days)

Unit factor = number of days in your chosen time unit

For months: ~30.5 days

For weeks: 7 days

For years: 365 days

Example:

Toothpaste lasts = 63.29 days
Tube price = $3
Selected unit = month (30.5 days)

Cost per month = 3 ÷ (63.29 ÷ 30.5) = 3 ÷ 2.075 ≈ $1.45/month

So, this toothpaste costs your household about $1.45 per month.

Summary

• You calculate how much toothpaste is used daily, considering how many people brush and how often.
• You adjust that amount to include paste wasted in the tube.
• You check how many days your tube will last at that usage rate.
• You divide the cost of the tube by how many “time units” (months/weeks) it will last, to get the cost per unit.