ISBLANK vs ="": the two kinds of empty
A cell can LOOK empty two ways: truly empty (nothing in it) or holding a formula that returns "". ISBLANK only believes the first; A2="" accepts both. Half of all 'my IF is wrong on empty cells' bugs are this distinction.
The differences at a glance
| ISBLANK | COUNTBLANK | COUNTA | |
|---|---|---|---|
| Truly empty cell | TRUE | Counted | Not counted |
| Formula returning "" | FALSE — there IS content (a formula) | Counted (!) — COUNTBLANK accepts both kinds | Counted — it's content |
| A space character " " | FALSE | Not counted | Counted |
| Zero | FALSE | Not counted | Counted |
| Compatibility | Universal | Universal | Universal — all verified in every version we test |
Which should you use?
- ISBLANK — You specifically need 'was anything ever entered here' — data-entry completeness checks where an IFERROR("") placeholder should count as filled.
- A2="" (or LEN(A2)=0) — The everyday 'looks empty' test — treats true blanks and ""-returning formulas the same, which is usually what the logic wants. TRIM(A2)="" additionally catches stray spaces.
Compatibility (Excel for the web, Sheets & LibreOffice executed; desktop Excel per docs)
All three behave identically across every LibreOffice build and in the Google Sheets run we execute (desktop Excel per Microsoft's docs — we do not run desktop Excel) — including COUNTBLANK's quirk of counting BOTH kinds of empty while ISBLANK accepts only one. The trio COUNTA/COUNT/COUNTBLANK don't partition a range cleanly for exactly this reason. Excel for the web is a separate application with its own calculation engine, and that one we do execute: all 10 corpus cases for these functions matched the documented values there (recalculated on OneDrive, 2026-09-01); the per-case values are on the individual function pages.
Example formulas
| Looks-empty test (usual choice) | =IF(A2="","missing","ok") |
| Never-entered test | =ISBLANK(A2) |
| Empty-ish incl. whitespace | =LEN(TRIM(A2))=0 |
Full per-version details on each function page: ISBLANK · COUNTBLANK · COUNTA.