You can change the data type of a dimension by right clicking the field -> Change Data Type -> Number
Then you can drag your field into the measures area to perform aggregations, etc.
If you had a problem converting your field with a calculation, you may have some characters in the field that causing the conversion to not work as expected.
Let's say your field is named [Percent] and it is a string data type
You should be able to create a numerical field by doing a simple FLOAT([Percent])
If the calculation or changing the data type didn't work, you probably have extra characters in your data.
If you still need help, post a sample of your data in a packaged workbook so we can take a look. Thanks!
I see what you are saying Corey. I think I have too many characters in my data which is breaking the chart. Is there a formula I can use to reduce the number of characters within the percentage? Or is this not fully the issue?
There are several String functions at your disposal: TRIM, LEFT, FIND, REPLACE, etc.
For example, if you wanted to keep only the first four characters, you'd use: LEFT([PercentStringField), 4)
See: String Functions
However, in order to truly diagnose your issue, we'd need to see some sample data that represents what you are seeing. Feel free to randomize a few rows of data and upload a Packaged Workbook (.twbx) file here.