Create a column using the Auto ID field type and name it “entrynumber”. This will automatically number your rows starting off at #1 and will incrementally count up from there.

Now, create a new field with a formula. The formula will check the entry number to see if it is within the 1-30 limit. The formula should look like this:

IF(entrynumber<30,“Valid”,“Invalid”)

If the entry is within 1-30, the field will say “Valid”, other wise if the entry number is over 30 it will say “Invalid.” Once you have that working, you can create a filter that will only display entries that are “Valid”

Hope that helps, let me know if you hit any snags.

I too was searching for a similar solution and found this - https://community.airtable.com/t/limit-the-number-of-workshop-registrations/35485/2 - which is a great way to limit registration. I wanted to share it with this thread too since this thread also helped.

Hey there,

Our miniExtensions form can do this without the need for a second table! We have a feature to only allow submission of a record under certain conditions. That feature, in combination with the formula field @Utility_Locator mentioned above can achieve exactly what you need! To make this work for new records you would need to turn on our form's Save & Continue feature as well, since formula fields are only defined once a record is created in Airtable. Save & Continue creates a temporary record in Airtable and therefore enables the use of formula fields on forms to create new records! Once the user actually submits the record, a checkbox can be checked to indicate that the submission has been completed. This way, temporary and submitted records can be distinguished easily!