Sooner or later someone asks you to build a membership card preview, a gift card mockup or a "download your staff ID" feature. The first question is always the same: how big is a card, really? The answer is more precise than "about 86 by 54", and getting it slightly wrong is how you end up with artwork that gets cropped at the printer.

This is the reference I wish I'd had: the numbers, the pixel maths, and copy-paste snippets.

The numbers

A standard plastic card (bank card, loyalty card, ID badge) is the ID-1 format from ISO/IEC 7810. The printing industry calls it CR80 .

Millimetres Inches

Width 85.60 mm 3.370 in

Height 53.98 mm 2.125 in

Corner radius ~3.18 mm 0.125 in (1/8")

Thickness (typical) 0.76 mm 0.030 in (30 mil)

Aspect ratio: 85.60 / 53.98 ≈ 1.586 : 1 (or 0.6306 the other way round). That's close to the golden ratio (1.618) but not equal to it, so don't reach for 1.618 as a shortcut.

You'll see 3.375 in quoted for the width in some printer drivers and US templates.…