What the calculator is doing
Two numbers describe any printed page and people routinely confuse them. The trim size is the paper itself, the sheet that arrives in the box. The safe area is the smaller rectangle inside it where content is guaranteed to survive the press. The calculator draws both to scale, so the relationship between them is visible rather than something you have to hold in your head.
Working out the safe area sounds like subtracting the margin twice, and for most formats it is. There is a detail that catches people, though, and it is the reason this page does not simply take the trim size and take a margin off every edge. Newspaper Club asks for a margin at the top, bottom and outside edge of a tabloid page, but says nothing about the inside edge where the fold is. Its traditional broadsheet asks for one on the inside as well. So the printable width of a tabloid loses a single margin and the printable width of that broadsheet loses two. The dataset behind this page records which edges each format applies its margin to, and the arithmetic follows the printer rather than an assumption.
The page count rule is not a suggestion
Newspapers are printed on large sheets which are folded and nested inside one another. One folded sheet gives four pages, which is why almost every format here requires a page count that is a multiple of four. You cannot order six pages any more than you can buy one and a half sheets of paper.
Newspaper Club's traditional broadsheet is the exception, running in multiples of two, because a broadsheet sheet is folded once rather than twice. It also has a much lower ceiling than the tabloid formats, twenty pages against sixty-four, which is worth knowing before you plan a long publication around it.
The practical consequence is that you should plan your content to a legal count from the beginning. If your material fills fourteen pages you are ordering sixteen, so decide early what the spare two will be. A picture page, a back cover, a contributors list or advertising all work. Discovering the constraint at the point of upload, with a deadline in front of you, is how people end up padding with clip art.
Bleed is a per-format question, not a per-printer one
If you have prepared files for brochures or posters, bleed is muscle memory: extend the artwork a few millimetres past the trim, add crop marks, export. Most of the formats here reject that outright. MakeMyNewspaper states that it does not accept bleeds and asks for a half inch of white around all four edges of every page. Newspaper Club asks for single pages in reading order with no crop marks and no bleed on its tabloid and broadsheet products. PrintNewspaper's 10mm white margin leaves nowhere for bleed to go.
Where a format takes no bleed, the design consequence is absolute: nothing can run to the edge of the paper. No full bleed photograph, no coloured band across the top, no reversed-out masthead touching the trim. Every element lives inside the margin, and a layout built around edge-to-edge imagery has to be rethought rather than adjusted.
The exception is the one that proves why this panel reads the format rather than the printer. Newspaper Club's traditional mini does require bleed, 5mm on the top, bottom and outside edge, so its document size is 175 by 260mm against a 170 by 250mm page. Anyone who learned the no-bleed rule from Newspaper Club's tabloid and applied it to the mini would submit a file 5mm short on three edges. The diagram above draws the bleed area whenever there is one, and the panel gives you the document size to set rather than making you add it up.
Reading the specification panel
The panel beside the diagram carries the rest of what the printer publishes: the resolution range for images, the smallest body text they will vouch for, and the date these figures were read from their guidelines. That date matters more than it looks. Printers change presses and revise their artwork specifications, and a spec sheet copied from a forum post three years ago is how people end up with trimmed text.
Everything here links back to the source it came from. If you are about to spend money on a print run, open the printer's own page and confirm the numbers still match. This site is a fast way to compare and plan, not a substitute for the preflight check your printer runs on the file you actually send.