01
A, B and C paper sizes: what the numbers actually mean
How ISO 216 paper sizes are derived, how A4 relates to A3 and A5, where B and C series fit, and how to set up a print file without guessing.
Read the guide →Guides
Where the numbers come from, and why conversions go wrong
Independent guides to paper standards, land area conversion and ID photo specifications, with formulas, common mistakes and checklists.
02
Mu, hectare and square kilometre: converting land area correctly
The exact definition of mu, how mu relates to hectares and square kilometres, and why land documents need more precision than a one-decimal converter.
Read the guide →03
ID and passport photo sizes: millimetres, pixels and head height
How to read an ID photo requirement, convert millimetres to pixels at the right DPI, and avoid the crop and background mistakes that cause rejections.
Read the guide →Every formula in these guides is also available as a calculator on the matching category page. Report a correction with the page URL and a source.