ISNUMBER

Determines if a text value is a number and returns TRUE if it is. Otherwise, returns FALSE.

Use

ISNUMBER(text) and replace text with the merge field name for the text field.

This function returns FALSE for blank values.
The ISNUMBER function is not aware of your locale. For example, ISNUMBER("123,12") and ISNUMBER("1 000") return FALSE even if the user's locale is “French.”
Chinese, Japanese, Korean, and special characters including a space return FALSE.
The ISNUMBER function returns TRUE for scientific formatting, such as “2E2” or “123.123.”

Validation Rule Example

OR(LEN(Bank_Account_Number__c) <> 10, NOT(ISNUMBER(Bank_Account_Number__c)))

This validation rule ensures a custom text field called Bank Account Number is a number of 10 digits and is not blank.

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