The Size My Sheet add-on allows you to see how close you are to hitting Google Sheets’ 10 million cell limit.
Install the add-on at https://workspace.google.com/marketplace/app/size_my_sheet/391759237464
After install you can launch the add-on via the Extensions menu to view a gauge in the sidebar.
The Size My Sheet add-on also allows you to insert a function within your sheet to retrieve the number of cells used or the percent used of the cell maximum that Google has set. It’s useful if you’d like to see these numbers in cells on the sheet rather than using the gauge in the sidebar.
To use this feature simply type one of the functions below into an empty cell of a Google Sheet with the Size My Sheet add-on installed.
Retrieve the number of cells used:
Retrieve the percentage used: