In Excel: use =ISNUMBER(value) — it returns TRUE for real numbers and FALSE for numbers stored as text, which is how you find a broken import.
On this page8
Syntax
Arguments
| Argument | required / optional | Description |
|---|---|---|
value | required | The value to test. TRUE only for real numbers, including dates and times. |
Related functions
Add a helper column beside the suspect data and type =ISNUMBER(.
Click the first cell, close the bracket and fill down.
Filter the helper column to FALSE to see every value that is not really a number.
For a contains test, wrap a SEARCH inside it: =ISNUMBER(SEARCH("text", A2)).
What this does
ISNUMBER tests whether a value is genuinely numeric. Its everyday importance is diagnostic: numbers imported from a web page or a CSV frequently arrive as text, where they look perfectly normal but are ignored by SUM, AVERAGE and every lookup that matches on a number. ISNUMBER down the column finds them instantly. It has a second, less obvious use — combined with SEARCH it becomes a contains-text test, because SEARCH returns a position when it finds something and #VALUE! when it does not. Keep the inputs visible and clearly labelled and the whole thing stays auditable — anyone who opens the file later, including you, can see at a glance exactly what feeds the result and change one assumption without hunting through the formula. For “isnumber function excel”, the reliable version is a short checking loop, not just the first command that appears to work. Run it on a deliberately small range first, watch how the affected formula change, and only then apply the same setup to the full sheet. When a formula is involved, keep the inputs labelled beside it, reference cells instead of typing values, and apply number formatting only after the result checks out. That is what makes a calculation you can defend to a CFO or an auditor useful in real work: repeatable, auditable, and not dependent on memory or luck.
A worked example
Auditing an imported column: =ISNUMBER(B2) filled down returns FALSE on every text-formatted number, and =COUNTIF(C2:C500, FALSE) counts them. As a contains test: =IF(ISNUMBER(SEARCH("urgent", A2)), "Flag", "") marks every row whose text mentions the word. ISNUMBER is the fastest diagnosis of the single most common data problem in spreadsheets: numbers that are not numbers. Check the referenced cells, argument order and result type in your workbook. Start with the worked example before changing an input, then compare the changed result with the calculation you expected. An error value or a result of a different type is a reason to inspect the inputs and arguments.
In Google Sheets
Google Sheets support for this task has not been verified. Check the function, arguments and workflow in the target product before transferring the example. Matching formula notation does not establish identical behaviour. The aim was to get you unstuck fast and leave you a little more capable than a copy-paste would. The answer is at the top and the detail above shows why it holds — so the next time a colleague asks, you can answer without reaching for search. For “isnumber function excel”, keep the input cells and the result visible while you check the formula in Excel. Follow the worked example and change one input at a time. The steps explain the workbook calculation; this page does not run a live calculator for that task.
Common mistakes
- Trusting appearance over the test — a right-aligned-looking number can still be text, and only
ISNUMBERsettles it. - Forgetting that dates and times are numbers, so
ISNUMBERreturns TRUE for them. - Using FIND instead of SEARCH in the contains idiom, which makes the test case-sensitive.
Frequently asked questions
How do I find numbers stored as text?
=ISNUMBER(A2) filled down returns FALSE for every one. Convert them with VALUE or Text to Columns.
How do I check if a cell contains specific text?
=ISNUMBER(SEARCH("word", A2)) returns TRUE when the word appears, because SEARCH returns a position on success.
Does ISNUMBER return TRUE for dates?
Yes — dates and times are stored as serial numbers.