Is there a way to tell if the bar spacing on a cage is too large before I house my rats in it and lose them?

It's 4' long 3' wide rabbit cage that I want to house my rats in now that they're full grown. I've added levels to it and it's very roomy, but I'm not sure if my two adult female rats can squeeze through the 1" bar spacing. I put them in it but they're too smart to try and escape with me watchig. Is there a way to tell if they can? Obviously I'll secure hardware cloth to it if it is, but I don't want to put more work into it if I don't have to.