The same word means different things at different printers
Tabloid and broadsheet are descriptions of a rough shape, not standardised measurements. Newspaper Club's traditional broadsheet is 380 by 578mm. Its digital broadsheet, sold alongside it, is 350 by 500mm, which is noticeably smaller in both directions. MakeMyNewspaper's broadsheet is 11 by 22 inches, a much narrower and taller shape than either. All three are correctly called broadsheets and none of them will accept the other's artwork.
This is the practical reason the table above exists. Choose the printer first and the format second, then take the numbers from that row and nowhere else. A dimension remembered from a previous job, or copied from a general article about newspaper sizes, is the most common way a layout ends up the wrong shape.
Reading the printable column
The printable figures are not simply the trim less twice the margin, and the difference is worth understanding. Newspaper Club applies its tabloid margin to the top, bottom and outside edge but not the inside edge at the fold, so the printable width loses one margin rather than two. Its traditional broadsheet applies the margin on the inside as well, so that one loses two. MakeMyNewspaper applies a half inch to all four edges of everything.
Each row here follows its own printer's rule. If you want to see the difference drawn rather than tabulated, the margin calculator renders any of these formats to scale with the trim edge and safe area marked.
Page counts, and why the last column matters
The final column is the multiple your page count has to fall on. Almost everything runs in fours because a folded sheet makes four pages. Newspaper Club's traditional broadsheet runs in twos, and it also has the lowest ceiling of any format here at twenty pages, which rules it out for anything long.
Plan to a legal count from the start. It is a much smaller problem at the outline stage than the night before a deadline, when the only remaining option is padding.