Here's how to limit text length using data validation in Excel:

1. Select the cell(s): Choose the cell(s) where you want to restrict the text length.
2. Data Validation: Go to the "Data" tab on the ribbon. In the "Data Tools" group, click "Data Validation."
3. Settings Tab: In the Data Validation window, ensure you're on the "Settings" tab.
4. Allow: Under "Allow," choose "Text Length" from the dropdown menu.
5. Data: This section defines the restriction type for text length:
- Between: If you want a minimum and maximum number of characters, select "Between" and enter the desired values in the "Minimum" and "Maximum" boxes. (e.g., Minimum: 5, Maximum: 20)
- Less than or equal to: If you only want a maximum length, select "Less than or equal to" and enter the maximum number of characters allowed. (e.g., Less than or equal to: 15)
- Greater than or equal to: For a minimum length requirement, choose "Greater than or equal to" and enter the minimum number of characters. (This is less common)
6. Click OK: Once you've defined your text length restriction, click "OK" to close the Data Validation window.

Now, when you try to enter text in the selected cell(s), Excel will only allow characters within the specified limits. If you attempt to enter more text than allowed, you'll receive an error message.