How to set the units to inches or millimetres

Open Edit > Preferences, or press Ctrl+comma, and go to the Units section of PDF by Zaweba. Choose millimetres, centimetres, inches or points, then press OK. Nothing changes until you press OK, so you can look around the settings first without worry.

Units sound like a small thing until you are working with someone else's measurements. A designer in the UK thinks in millimetres, a print shop may quote in points, and a client in the United States sends specifications in inches. Setting the app to match the job saves a lot of converting in your head.

The four choices

Millimetres suit most work in the UK and Europe, including paper sizes in the A series and most architectural drawings.

Centimetres are the same scale with fewer digits, which some people find easier for page sizes and margins.

Inches are the standard for American paper sizes such as Letter and Legal, and for anyone working to American specifications.

Points are the unit of type and of the PDF format itself, at 72 to the inch. They're handy for precise work on text and layout, where a font size and a line spacing are already given in points.

Changing the unit

Choose Edit > Preferences. The window has a search box, so typing "units" takes you straight there. Select the unit you want. Press OK.

If you change your mind, come back and choose another, or reset the section to its default.

Which unit for which job

Match the unit to whoever you're working with. If a print shop asks for 3 mm bleed, work in millimetres. If an American client asks for one-inch margins, switch to inches for that job.

Know what stays the same. The rulers in View > Rulers and grid are marked in millimetres, whatever you set here. The grid spacing for those rulers is set separately, in Preferences > Page display.

Remember paper sizes in printing are their own thing. The Print window lets you pick standard sizes, Same size as the PDF page, or a custom size you can save, so printing on US Letter or A4 doesn't depend on this setting.

In a shared office

If everyone in a team should use the same unit, an administrator can set it once for all of them. A defaults.json file in the Zaweba PDF folder under ProgramData, or beside the program, gives default values, and can lock a setting so it always takes the administrator's value and is greyed out in Preferences. Units are a sensible thing to set as a default but leave unlocked, so individuals can still switch for a particular job.

The rest of Preferences

While you're there, it's worth a look at the other sections. Preferences has searchable sections for General, Page display, Documents, Commenting, Forms, Identity, Full screen, Search, Signatures, Security and trust, Spelling, Language, Reading, Accessibility, Colour management, Content editing, Convert and Measuring, as well as Units. Any section can be reset if you get it into a muddle.

Choosing your units is a one-minute job in PDF by Zaweba, and it makes every measurement you see afterwards make sense at a glance.