We don't know exactly how many Conservative Party members there are because - unlike the UK's other parties - the Conservatives don't regularly release the figures.
The last time they did so was back in March 2018, when they put the figure at 124,000.
That's larger than some of the more pessimistic guesstimates, but way down on the peak of nearly three million that the party boasted in the early 1950s.
https://www.bbc.co.uk/news/uk-politics-48395211
Brexiteer entryists may have pushed that number up, natural wastage has surely pushed it down.