Limit number of characters in a cell

I want to limit the number of characters that can be put into a cell to be 20.

Is it possible when character count exceeds 20, disable input into the cell and trigger a pop-up message that shows how many characters I'm attempting to input into a cell?

If that is not possible, how can I conditional format to change to a color when character count limit is exceeded?

thanks!

Using Data Validation for the cell, i.e A1:
Data/Data Validation:
In Setting tab:

Allow: Text length
Data: less than or equal to
Maximum:20

In other tabs: for warning messages

The paste operation is a drawback of validation.

You could use an event macro if you can get someone to write the code (I'm not much of a programmer).

Here's how to use conditional formatting to highlight cells with more than 20 characters.

Let's assume you want to apply this to the range A2:A10.

Select the *entire* range A2:A10 starting from cell A2.
Cell A2 will be the active cell. The active cell is the
one cell in the selected range that is not shaded. The
formula will be relative to the active cell.

Goto the Home tab>Styles>Conditional Formatting>
Manage rules>New rule>Use a formula to determine
which cells to format

Enter this formula in the box below:

=LEN(A2)>20

Click the Format button
Select the desired style(s)
OK out

You're welcome!

the validation answer is the way to go.
Link here to disable paste
http://www.mrexcel.com/forum/excel-q...ste-excel.html

You'll also have to disable drag and drop. That's another drawback of validation!