It's hard to validate the average number of words per page or the total number of pages in an eBook beforehand but there is a method to find how many pages we will end up with, in our eBook. Just use the Kindle Previewer tool. Alternatively, you can also use the Online Previewer tool within Amazon KDP. I'd recommend the desktop version (Kindle Previewer) as it offers more options, comparatively.
Remember: even if you find out that your eBook comes to a specific number of pages while previewing, it will vary in the real-world, for your readers. That's because every person's ereader device (or mobile phone) and their Kindle settings will be different. Different font face, font size will all make it almost impossible to exactly predict the number of pages our eBooks will have.
All we can do is deduce at a range of page numbers that we may end up with, using different font options within the previewer tool.