You might find this useful - Fermi problems: https://en.m.wikipedia.org/wiki/Fermi_problem https://en.m.wikipedia.org/wiki/Fermi_problem You could make a rough

You might find this useful - Fermi problems: https://en.m.wikipedia.org/wiki/Fermi_problem https://en.m.wikipedia.org/wiki/Fermi_problem You could make a rough model based on educated guesses and perhaps not even be that far off the actual number.