Market Sizing Calculator
Top-down sizing is three multiplications, and its weakness is that the errors multiply too. Seeing the final figure as a fraction of the starting population is usually the sanity check that lands.
The calculator
Enter your figures and press Calculate.
Every percentage is yours. No market size, penetration rate or conversion assumption is supplied here.
How it works
Every line of the result is derived from the numbers in the boxes above and nothing else. The working is printed step by step so you can check it, disagree with it, or redo it on paper.
What it does not do
It supplies no rates, no benchmarks and no view on what a good number looks like — those depend on your situation and belong to you. Nothing is sent anywhere or stored.