Here are two methods to restrict data entry to only numbers in Excel:

Method 1: Using Data Validation

1. Select the cells: Choose the cell(s) where you want to allow only numeric input.
2. Data Validation: Navigate to the "Data" tab on the Excel ribbon. In the "Data Tools" group, click "Data Validation."
3. Set Allow to "Custom": In the "Settings" tab of the Data Validation window, under "Allow," choose "Custom" from the dropdown menu.
4. Formula for Numbers: In the "Formula" box, enter the formula `=ISNUMBER(A1)`. Replace "A1" with the actual cell address you selected in step 1. This formula checks if the entered value is a number and returns TRUE if it is, allowing the entry.
5. Error Message (Optional): You can customize the error message displayed when someone tries to enter non-numeric data. Click the "Error Alert" tab and set the desired style, title, and error message.
6. Click OK: Click "OK" to close the Data Validation window and activate the restriction.

Method 2: Using Cell Formatting (Limited to Whole Numbers)

1. Select the cells: Choose the cell(s) where you want to allow only numeric input.
2. Number Format: Right-click on the selected cells and choose "Format Cells" from the context menu.
3. Number Tab: In the "Format Cells" window, click on the "Number" tab.
4. Choose a Number Format: Select a number format category (e.g., Number, Currency, Accounting). These formats typically restrict entries to numeric values.
5. Decimals (Optional): You can specify the number of decimal places allowed if you want to restrict to whole numbers, choose "0" decimals.
6. Click OK: Click "OK" to close the "Format Cells" window and apply the format.

Note: While cell formatting restricts most non-numeric entries, it allows pasting text as values. Data Validation offers a more robust approach for all scenarios.