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When it comes to size distribution it can differ a bit from country to country. You can take a look at this chart from 2016 when it comes to t-shirt purchased worldwide:
The distribution often resembles a Gaussian distribution curve (google it if you are not familiar).
In your case when you have 4 sizes, our recommendation would be to start with a ratio of 1:2:2:1 (where you produce most of M & L for men and most S and M for women).When it is time to produce more garments you can look at your own sales data to make adjustments to the distribution ratio, that is more tailored to your brand’s situation.