Why Conditional Fields Validating the Hidden Fields? I have preset sizes like small, medium and large and an option to provide custom size. If some one selects custom option from a select list the measurements fields appears through conditional fields and if some one select small medium or large the measurements fields hides.

The problem is when I am submitting a form by selecting Small, Medium or Large option from select list it gives error that measurements fields are required.

I have tried to add additional condition to make the fields optional if the select list has the values small, medium or large but still getting the same error.
Check that your measurements field isn't set as required in the field settings in content types. You could also provide a default of 0 I guess.