COUNTBLANK walks through every cell in the range and counts the cell if it is empty or if it contains a formula that evaluates to an empty string. Truly empty cells — cells that have never been touched or have been cleared with the Delete key — are counted. Cells containing a formula like =IF(A1>10,"High","") that evaluates to "" are also counted because from a display perspective they look empty even though technically they contain a formula. This matches what most people mean when they say "blank". The function accepts any range, including multi-column ranges like A2:D100 — it simply totals all the empty cells in that rectangular area. There is no criteria argument; COUNTBLANK is hard-wired to count blanks specifically. An equivalent alternative is =COUNTIF(range,"") which returns the same count in almost every scenario. The
COUNTBLANK function is cleaner and more self-documenting, so I use it by default. For the inverse count — cells that do have a value — use the
count non-blank cells formula with COUNTA instead.