I have a field for "Length" regarding some data collected in the field. Unfortunately the "ft" after the number for the length had spaces or no spaces or a weird format, but basically I want Length to look like this: "9 ft" - "7 ft" - "8 ft" ...etc. At the moment it just says, "9, 7, 8." Anybody know how to fix this in the field calculator in ArcGIS Pro?
If the Length field is numerical (e.g. integer or floating point) then you cannot include text in that column. The benefit of having the field be numeric is that you can use it in queries, classification, and calculations if you decide down the road to do any analysis on your data.
If you would like to indicate in the table that the length measurement is recorded in feet then you can change the heading to something like "Length_ft". This will only change the heading and the column data will not change and will still be numeric.
If you would like for the labels on your map to indicate that it the measurement is in feet then you can edit the labels to include "ft" or you can just indicate that the measurement is in feet in your legend heading.
If you are absolutely sure that you will never want to do any symbology classification or analysis then you can convert the field to string and add "ft" in the field (as outlined in the chosen answer.) Once you do this, you lose the functionality of a numeric field.