I'm talking about the US (because US statistics are so readily available online), but it probably also applies to other Western countries. Globally, the proletariat has now become the largest class.
IRS statistics confirm that you have to go even smaller than the top 1% of American "earners" to find a group most of whose income comes in the form of *capital* income. To this, add the top executives, top bureaucrats, top military officials, judges, hedge fund managers, etc., and the figure still probably doesn't come close to 5%.
Then I estimated the number of petite bourgeois, based on the official US census. As a percentage of the workforce or of the working-age population, 15% seems reasonable, maybe 20, maybe less than 15. As you'll see, that's a liberal estimate. There are around 6 million small business employers in the US. To these, add middle management (less than 5 million), and the professionals: 7 and a half million legal and business professionals (lawyers, financiers, including accounts, and marketing experts, including sales & PR), as well as almost 6 million STEM, medical and academic professionals, closer to 9 million now if you account for the rapid growth of the software engineering occupation (professors, scientists; engineers, architects; physicians, dentists, opticians, audiologists, podiatrists, and pharmacists). You could also add journalists, authors, psychologists and such, if you want, but that's less than a million.
Now consider the lumpenproletariat. The unemployed, unemployable, unsteadily employed, etc. The employment-to-population ratio (0.674 in the US) is not an impeccable measure because it doesn't account for the fact that a large proportion of the 15-to-64-aged population is still in school, but neither does it account for those who are insecurely employed. I have seen at least one other source, not in my possession now, suggesting a "declassed" population of 30%. This is without counting financial dependents who are stay-at-home spouses.
Finally, that leaves us with a 50% of steady-proletarian population.
The majority of the Medieval population was made up of peasants, so it's not surprising if the majority of the Modern one is proletarians.