How to Check for Numbers with ISNUMBER in Excel

Catch numbers stored as text and other bad imports with ISNUMBER before they break your totals.

You will learn to

• Test whether a value is a real number
• Only calculate when the input is numeric
• Tell numbers, numbers-stored-as-text and junk apart

How it works

ISNUMBER(value) returns TRUE only for real numbers — including dates and formula results — and FALSE for text, even when the text looks like a number. That makes it the quickest way to find imported values such as "45" that SUM silently ignores.

To tell a number stored as text from genuine junk, try converting it: ISNUMBER(--B4) is TRUE for "45" (the double minus turns it into 45) but FALSE for "12 kg", which cannot convert. Wrap the test in IF to calculate only with clean values.

=IF(ISNUMBER(B3),B3*C3,"Check weight")