Can I hide a field when the TOTAL of a certain answer reaches a limit?

I want to close registration for a class once its capacity has been reached.  So I want to base the condition on all responses received to date, by the form, not just the one user's responses.

If you wish to close the registration for a class once its capacity has been reached, then you can set the submission limit on the form so that the will be disabled automatically, once it reaches the limit.

Here is the guide: How-to-Limit-Submissions-in-a-Form

In case, if you have different classes on the form and which to set the capacity for each class, then you may try using the appointment slot widget.

If you wish to hide a field based on the value of another field, please follow this guide: How-to-Show-or-Hide-Fields-Base-on-User-s-Answer

if you need any further assistance, please provide more information along with the form URL so that we can check.

that's very helpful but the way our form is set up we have multiple classes available (a list of options as radio buttons), and only want to close the ones that are full, while still allowing registration in the other ones.  Any way to do that?

Instead of a radio button field, you can use the appointment slot widget to meet your requirements.

Please give it a try and let us know if that works for you.

that's great!!!!  thanks!