ATM and credit card size in cm, mm and inches, and how to use a card as a ruler
The short answer
A standard ATM, debit or credit card measures 85.6 mm by 53.98 mm, which is 8.56 cm by 5.398 cm or about 3.370 by 2.125 inches. The size is fixed by the ISO/IEC 7810 ID-1 standard, so every bank card, most ID cards and most driving licences are exactly the same. That makes a card a reliable ruler for small objects and the reference an online ruler uses to set its scale.
A bank card is one of the few objects that is exactly the same size in every wallet in the world. That makes it more than a way to pay. It is a ruler you always carry, and it is the reason an online ruler can be accurate.
The exact size
| Width | Height | |
|---|---|---|
| Millimetres | 85.6 mm | 53.98 mm |
| Centimetres | 8.56 cm | 5.398 cm |
| Inches | 3.370 in | 2.125 in |
| Rounded | 8.6 × 5.4 cm | 3 3/8 × 2 1/8 in |
The size comes from the international standard ISO/IEC 7810, which defines the ID-1 card format. The standard also sets the thickness at 0.76 mm and gives the corners a small rounded radius.
Which cards follow it
- Credit, debit and ATM cards, everywhere
- Most national ID cards and residence permits
- Most driving licences, including UK and EU photo cards and US licences
- Most hotel key cards, transport cards and gift cards
Loyalty cards and membership cards are usually ID-1 too, but some are not. For measuring, use a bank card: those are made to the standard.
Measuring with a card
With the width and height known, a card is a short ruler:
- Width, 8.56 cm. Good for anything up to about 8 cm.
- Height, 5.4 cm. A second fixed length.
- Thickness, 0.76 mm. Stack ten cards and you have 7.6 mm, which is handy for gaps.
- Diagonal, about 10.1 cm. Corner to corner, if you need a longer reach.
For longer things, walk the card along the object and count, marking each step lightly with a pencil. The guide to measuring without a ruler covers A4 paper, coins and other everyday references too.
Why online rulers need a card
A web page cannot find out how big your screen is. Browsers work in CSS pixels and assume 96 of them to an inch. Real screens range from about 90 to more than 450 physical pixels per inch, and the browser scales in between. An on-screen ruler that trusts the 96 figure can be out by 30% or more.
The fix is a reference object. The online ruler shows an outline of a card. You hold a real card against the glass and press + or − until the outline matches its edges. Now the page knows how many pixels make 85.6 mm on your screen, and every length it shows is true to size.
The calibration is kept on that device, in that browser, and every measuring tool on the site uses it. You are asked again only if you change the browser’s zoom, because zoom changes the size of everything on the page.
A card beats a coin
The ruler also accepts a coin: a ₹10 coin (27 mm), a US quarter (24.26 mm), a €1 (23.25 mm) or a €2 (25.75 mm). A card is more accurate, for one reason: length. A one-pixel slip when you match an 85.6 mm card is a small share of the whole. The same slip on a 25 mm coin is more than three times as large a share.
After calibration, the ruler states its own margin of error for your screen: roughly 0.2 mm on a phone and 0.3 mm on a laptop.
Tips for an accurate match
- Look straight on. Glass has thickness, so from an angle the card and the outline shift against each other.
- Match the long edge. Line up the left edge, then adjust until the right edge meets the outline exactly.
- Leave browser zoom alone. If you zoom, calibrate again.
The same calibration powers the ring sizer, which measures a ring’s inside diameter on your screen and converts it to Indian, US, UK, EU and Japanese sizes.
- Measuring
