Which series is longer? Naruto or Bleach?

Naruto, I think.

Bleach technically since it has a larger volume catalogue.

More chapters = longer story.

If a comic series has 300 issues collected in 43 Volumes (7 issues per volume), Its a longer comic series than one with 250 issues collected in 50 volumes (5 issues per volume). Each volume just has more issues in it in the first series.

The real way to do it is to compare total page numbers

Well then it's definitely Bleach considering Volumes tend to be 170-200 pages long, and Bleach has two more of that than Naruto.

Naruto I think.

Naruto seemed longer to me, although I could be wrong about that.