Hi there,

Happy to help/clarify!

Is it very rarely that the market sizing question would be focused at a global level, rather more at a country level? Say if the question is revised to estimate the jewellery market for China? What would be your feedback on the below approach?

Not rare at all! There are plenty of global questions like "Estimate the number of internet users online right now" or "How many fish are eaten globally per day". The same questions can be asked locally. There's no rule here!

1/ China Population

2/ Share of Rural / Urban population (rural population may have less access and would spend much less per year, can we safely assume they are negligible even after considering online channels?)

Hmmm I wouldn't say rural is negligible. I would take x% of whatever you calculate for Urban, and apply it here. I would probably take about 10% but I don't know China as well as you!

3/ Urban population by income (like you mentioned, is it better to segment them into high, middle, low income segments rather than into exact income range? also can I safely neglect low income segment)

Yes, do high middle and low. I think you can neglect low income if we're talking luxury jewelry. If we're talking all jewelry you cannot neglect low income as they might make a cheap purchase or two.

4/ Divide urban high income and middle income population by male / female, find average of spend by income group, assume high income male would purchase the same amount as high income female if not more (through gifting to their partners and family members) and assume middle income male would shop less then middle income female (occassional gifting)

This is overkill. You are adding more detail/complexity without getting any more accurate. Anything you say here is guessing.

5/ Multiply average spending with the segment population by income level and sum them up = total market size Would you say there is another approach to estimate the market to serve as validation?

When I teach market sizing to my students I always emphasize the importance of memorizing certain key characteristics of a country. One of these is the market size of the key industries (financial, healthcare, retail, etc.). You'll want to compare your jewelry size to the retail market size that you already know. If it's >1% and <10% you're probably safe!