Formula Guide

The Excel ISNUMBER Function
explained simply

ISNUMBER checks whether a value is a genuine number, returning TRUE or FALSE — useful for validating data before calculating with it.

ExcelPro · 3 min read · Updated June 2026
Contents
  1. What does ISNUMBER do?
  2. Syntax
  3. 3 examples
  4. FAQ

What does ISNUMBER do?

ISNUMBER tests whether a value is a real number, returning TRUE if so and FALSE if it is text, blank, or an error.

It is most commonly used to validate imported or user-entered data before running calculations on it, since a "number" that was actually typed or imported as text will silently break math formulas.

Syntax

=ISNUMBER(value)
ArgumentDescription
value requiredThe value or cell to test.

Examples

Example 1
Check if a cell contains a real number
=ISNUMBER(A2)

Returns TRUE if A2 holds a genuine number, FALSE if it holds text or is empty.

Example 2
Catch numbers stored as text
=ISNUMBER(A2)

A common gotcha: numbers imported from some systems are stored as left-aligned text and will return FALSE here even though they look like numbers.

Example 3
Validate before calculating
=IF(ISNUMBER(A2),A2*2,"Invalid")

Only doubles A2 if it genuinely is a number, avoiding a #VALUE! error on bad data.

Common mistakes

⚠️ Assuming a number-looking cell passes ISNUMBER

If imported data is actually text, ISNUMBER correctly identifies it as not a real number, even if it visually looks numeric.

FAQ

How do I convert text that looks like a number into a real number?
Use the VALUE function, or multiply by 1, to convert text-stored numbers into real numeric values.

Practise ISNUMBER with real data

ExcelPro has hands-on ISNUMBER exercises built into real job scenarios — free to start.

Try ISNUMBER exercises →

Related formulas

ISTEXT ISBLANK VALUE