Open the spreadsheet document you'd like to apply the text restriction to.
a) Click the "Data" tab, then click "Data Validation."
b) Click "Settings."
c) Select "Text Length" in the "Allow" field.
d) Select "Less than or equal to" as the rule type.
e) Enter the maximum number of characters you'd like to allow in the text field.
f) Select "Ignore blank" to not count spaces and other blank characters toward the text limit. If spaces should count toward the limit, leave this unchecked.
g) Type an optional message that will be displayed to the user if he/she attempts to enter too much information in the "Input Message" field.
h) Select "Show error alert after invalid data is entered" to make sure the user receives a notification that his text was not entered. Select the ‘stop’ option which will give them an option to retry (if you select a warning, it will still allow the user to exceed text)
Click "Save" to save your document.
i) When you click on the restricted cell, a message will appear
j) If you exceed the maximum capacity, a message will appear
See attachment