How does one feel confident about solving guesstimates?

You have actually nicely pointed out some of the common segmentation parameters.
0) Population / Household - It is good also to prepare a table of population of various countries
1) Geography split - I don't remember exactly where this can be useful.
2) Age wise split - For this, it is good to prepare a table of life expectancy of various countries. This will also help you with the replacement concept.
3) Gender split - This is quite straightforward and often a 50:50 split is taken. But not really effective for market sizing unless it's a gender-specific product
4) Income split - This is useful and again would be great to prepare how the income distribution in developing country and in developed country would look like. Income equality is a default option, but not always true.
5) Replacement concept: This is a great tool to estimate market demand for any consumer product based on population size and lifetime of the product.
This is almost all that you can do.

Hi Anonymous,

market sizing usually doesn’t require much information to be memorized. The main data I would recommend to know are:

1. State populations, in particular for the area you live in. So for Europe, knowing the population of Spain, UK, France, Italy Germany, Russia and the main countries in Eastern Europe would help.
2. Formulas for volume/surface of solid figures - sphere, cylinder, pyramid, parallelepiped, cone.

Knowing the number of companies in your own country could also come handy if you end covering something related to that.

As mentioned, once you know the previous data, you should be able to estimate all the other numbers with an appropriate justification.

Best,

Francesco

I am Germany based and I found it useful to additionally to what you mentioned to know the revenue and number of employees for the main German companies (VW, Siemens, BASF, Daimler). Otherwise I would say it's not necessary to memorize anything, if you can make justified assumptions.