How to calculate how big the shell opening needs to be for a crab?

[Reet]

I have 3 purple pinchers, have owned them for 3 years, two medium and one large now, and am in need of help figuring out what size of shells they need now that they are getting larger. The ones i had ended up getting banged up and are now unsuitable for them. I am buying natural grown turbos/conches currently off of amazon (unless there's a better place?) and need help figuring out how large the openings need to be for my crabs. The size won't help if they can't fit.



This one is my biggest, and although this shell seems ok for him now I want to make sure I have others he can fit in on hand, him taking this one was a lucky strike.



The other two are about this size, and I need shells for them to grow into but don't want them to be too large nor too small, and the ones they are wearing have been chipping a bit and that's a struggle I've had a lot with their shells. If you guys know why their shells are cracking and chipping that would be nice, they seem to naturally degrade.

Don't worry about their tank size, I'm upgrading it to a tank like 2 times the size of this one, and might get a fourth buddy (though I'm unsure where to get one because they say to avoid stores and online but I'm in Wisconsin and there's not a lot of crab places here?)

[I<3mycrabbies]

Hi!
To measure the shell opening you take a ruler and you go from where the opening connects to the rest of the shell and you measure to go to where the farest point is. Make sure when you order them you look for shell opening for size and not just size.
I hope this helps!

[curlysister]

Naples Sea Shells has a page that shows how to measure:

https://naplesseashellcompany.com/sizematters.html

As for where to get another hermit crab, be sure to check out adoptions pages. And you can also watch local buy and sell pages, or even put a 'wanted' ad on them. I got all of my crabs from people who no longer wanted or were unable to continue to care for them - and I live in the middle of the Canadian prairies!