This Excel keyboard shortcut is powerful, but it has a few quirks you need to be aware of. Its quick to use because the A and Ctrl keys are so close together.
The shortcut works slightly differently depending on where the active cell/range is, and what is around the active cell/range. The way I think of it is that the A stands for ALL.
Surrounded by blank cells
If the selected cell/range is surrounded by blank/empty cells then the shortcut will select the whole sheet.
In a Table Structure
If the selected cell/range has adjacent cells then the shortcut works like the Current Region option and it will select all the cells including the adjacent cells up until it hits blank rows and columns. This is great for selecting table layouts. See note below about Formatted Tables.
Shortcut Pressed Twice
This is where Ctrl + A is a bit different. If you press it once and it selects a table, you can press it again to select the whole sheet.
In A Formatted Table
The shortcut works a little differently in a formatted table (a table defined by using the Format as Table option in the Home ribbon). If you have a cell selected in the formatted table when you first press Ctrl + A it selects the data only in the table – not the headings. This is handy if you only want to copy the data. Pressed again it will include the headings and the data and pressed once more it will select the whole sheet. That’s right you can press the shortcut three times.
Current Region Alternative Shortcut
I use the Ctrl + * shortcut to select the current region (I use the * on the numeric keypad). Otherwise it is Ctrl + Shift + 8. If you have a cell/range surrounded by blanks then the selection doesn’t change. If you have a cell in any table it selects the data as well as the headings. It also stops the selection at blank rows and columns. You only ever press it once.
You can use this shortcut in dialogs that list entries. Press it to select all the entries – the Find dialog is an example. It selects all the “found” cells.
It works in the other Office apps as well as Windows.
To select all the text in a Word document press Ctrl +A.
To select all the files in a folder use Ctrl + A.
If in doubt give it a try, you will be surprised in how many situations it works.