MM Ruler: measure in millimetres, precisely
Any standard bank, credit, debit, or ID card works: the ISO/IEC 7810 ID-1 format is exactly 85.60 mm wide everywhere in the world. Hold the card flat against the screen, match the width, then apply.
A millimetre ruler for the measurements that punish errors
Beads, gemstones, watch straps, screws, seals, and SIM trays live in millimetres, where being off by two ticks ruins the order. This page loads the metric ruler with every millimetre marked, and the marker readout reports spans under a centimetre directly in millimetres to one decimal place. Calibration matters double here: it takes 30 seconds against a bank card, and on a typical 20 mm measurement even a 1 percent calibration error is only 0.2 mm, which is the precision realistic for measuring against glass. The measure box handles small objects held to the screen in both dimensions at once.
Standardized sizes in millimetres
| Object | Size | Source |
|---|---|---|
| Bank card | 85.60 × 53.98 mm, 0.76 mm thick | ISO/IEC 7810 ID-1 |
| Nano-SIM card | 12.3 × 8.8 mm | ETSI 4FF specification |
| US quarter | 24.26 mm diameter | US Mint coin specification |
| CD / DVD | 120 mm diameter, 15 mm centre hole | Disc format standards |
| Common watch strap widths | 18, 20, or 22 mm at the lug | Industry-standard lug widths |
Millimetre precision on glass: what helps
The error budget starts here
A half-millimetre mismatch when matching the 85.60 mm card is roughly a 0.6 percent scale error everywhere. Take ten extra seconds at the card's edges and the whole ruler inherits the care.
Kill the parallax
An object held against the screen sits a millimetre or two in front of the pixels, so viewing at an angle shifts the reading. Look perpendicular to the glass, close one eye for fine work, and centre the object in your view.
Read the chip, not the ticks
Squinting at millimetre ticks invites rounding; the draggable markers do the subtraction for you and report to a tenth of a millimetre. Place, read, done.