Unless otherwise agreed with Jisc in writing, there is a cap on the number of responses for any single survey of 20,000. If you expect that your survey will collect more than 20,000 responses, you should contact help@jisc.ac.uk.
Online surveys allows you to set expected responses and maximum responses numbers in your survey’s 
Distribution settings. You do not have to provide numbers in these fields. The survey responses options are there to assist you in the administration of your survey but you do not have to use them if they are not relevant to your survey.
Expected and maximum responses numbers are explained in more detail below.
Expected responses
The Expected responses number is the number of responses you think your survey will gather. This is set to 100 by default but this is not a limit and can be changed or removed at any time, even after your survey has been launched.
If you have not set up a list of respondents, the expected responses number is used to calculate the response rate that is displayed on the survey launchpad. For example, if your expected responses number is 100 and you have received 10 responses, the response rate displayed on the survey launchpad will be 10%.
Maximum responses
The Maximum responses field allows you to set your survey to automatically close when a particular number of responses has been received. If you set a maximum responses number your survey will close when that number of responses has been submitted. The maximum responses number can also be changed at any time.
Maximum responses is blank by default. Please only provide a number in the maximum responses field if you want your survey to automatically close when that number of responses has been submitted. The maximum responses number does not affect any other aspect of your survey and should be left blank if you do not wish to limit the number of responses your survey can receive.