ISBLANK
=IF(ISBLANK(A1), "Empty", A1*2)
Test whether a cell is truly empty. Different from testing ="" — ISBLANK matches only genuinely blank cells, not empty strings from formulas.
Information Functions
Test values, catch errors early, and build bulletproof formulas. Information functions are how professional Excel users make their workbooks safe against messy data.
Information functions don't calculate anything — they answer questions. Is this cell blank? Is this a number or text? Did this formula produce an error? What kind of value is in this cell? Wrapping normal formulas in information tests turns fragile calculations into resilient ones that gracefully handle missing data, wrong types, and edge cases.
The essential four
ISERROR / ISERR / ISNA
=IF(ISERROR(A1/B1), 0, A1/B1)
Test for errors. ISERROR catches every error. ISERR catches all errors except #N/A. ISNA catches only #N/A. Pick the one that matches your fallback strategy.
ISERROR Family Guide →ISNUMBER
=IF(ISNUMBER(A1), A1+B1, "Not a number")
Test if a cell contains a number (not text-that-looks-like-a-number). Essential when importing CSV data where "123" might be text or a real number.
ISNUMBER Complete Guide →CELL
=CELL("format", A1)
Return metadata about a cell — its format, address, contents, filename, sheet name, or type. Useful for building dynamic references and debug tools.
CELL Complete Guide →All 20 information functions
- ISBLANKCell is truly empty
- ISNUMBERValue is a number
- ISTEXTValue is text
- ISNONTEXTValue is not text
- ISLOGICALValue is TRUE/FALSE
- ISERRORAny error type
- ISERRError, but not #N/A
- ISNAOnly #N/A error
- ISREFValue is a reference
- ISFORMULACell contains a formula
- ISEVENNumber is even
- ISODDNumber is odd
- ISOMITTEDLAMBDA arg is omitted
- NAReturn #N/A explicitly
- CELLCell metadata
- TYPEData type of value
- ERROR.TYPEWhich error occurred
- INFOEnvironment info
- SHEETSheet number
- SHEETSTotal sheets in workbook
Common defensive formula patterns
- Safe division:
=IF(B1=0, 0, A1/B1)— prevent #DIV/0! errors - Safe VLOOKUP:
=IFERROR(VLOOKUP(A1, table, 2, FALSE), "Not found")— see also our Logical functions hub - Blank check with fallback:
=IF(ISBLANK(A1), "N/A", A1) - Number-only calculation:
=IF(ISNUMBER(A1), A1*1.1, "Invalid input") - Sum only numbers in a range:
=SUMPRODUCT((ISNUMBER(A1:A100))*A1:A100)
Frequently asked questions
ISBLANK vs ="" — what's the difference?
ISBLANK returns TRUE only for genuinely empty cells. =A1="" returns TRUE for both empty cells AND cells containing empty strings from formulas (like =IF(condition, "value", "")). Use ISBLANK when only true blanks should match.
Should I use ISERROR or IFERROR?
IFERROR is shorter and cleaner for the common case: =IFERROR(formula, fallback). Use ISERROR when you need to test for errors in a condition without providing a value: =IF(ISERROR(A1), "check", A1*2).
Why does ISNUMBER return FALSE on my imported numbers?
Because they're text that looks like numbers. Common with CSV imports. Convert with =VALUE(A1) or select the range → Data → Text to Columns → Finish to bulk-convert.
What does the CELL function return that isn't obvious?
CELL can return the filename (=CELL("filename")), sheet name, cell address, format code, and column width — useful for building dynamic references and self-aware workbooks.
Is ISFORMULA useful in real work?
Yes — for auditing large workbooks. Combined with conditional formatting, ISFORMULA lets you highlight every cell containing a formula (usually shown in a different color) so you can visually distinguish inputs from calculations.
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