Credit Card Size in Inches, cm and mm

The exact dimensions

A standard credit card measures 85.60 × 53.98 mm. In other units:

The conversion uses the exact definition 1 in = 25.4 mm, while the table rounds to three decimal places: 85.60 / 25.4 ≈ 3.370 in and 53.98 / 25.4 ≈ 2.125 in. The short edge rounds to the familiar fraction 2 1/8 in, but exactly 2 1/8 in is 53.975 mm, so the specified edge is 0.005 mm longer. A few derived numbers are useful too. The aspect ratio is 85.60 / 53.98 ≈ 1.586. The area is about 46.2 cm² (7.16 in²). The diagonal is sqrt(85.60² + 53.98²) ≈ 101.2 mm, or 3.98 in.

Where the size comes from

ISO/IEC 7810 defines several identification-card formats; payment cards are normally made to its ID-1 format. ID-1 defines the 85.60 × 53.98 mm outline and related geometry. Companion standards cover features such as magnetic stripes and contact chips.

The fixed format lets compliant cards work with ATMs, payment terminals and readers built to matching dimensions. It does not mean that every identity, membership, loyalty or handmade card is ID-1. Before using a card as a measurement reference, confirm that it follows ID-1 rather than assuming from its purpose or appearance.

Other things that are the same size

Because ID-1 is a general identification-card format, not a banking format, many other cards are produced on the same blanks:

• Debit, credit, prepaid, and most gift cards
• Driver's licenses in many countries, including the United States, Canada, the United Kingdom, and the European Union
• National identity cards and residence permits in many countries
• Loyalty, membership, and transit cards
• Hotel key cards and office access badges
• The original full-size SIM card carrier (the plastic frame a mini-SIM is punched out of)

Cards that are not ID-1 do exist. Some business cards, library cards, and older laminated paper cards use their own sizes. If a card has square corners, feels thin, or has no stripe or chip, do not assume it is 85.60 mm without checking.

Why it is the ideal screen-calibration reference

A browser cannot read the physical size of a display; it only knows the screen in CSS pixels and assumes 96 of them per inch. To draw a true-to-life ruler, the page needs a real-world object of known size to compare against. A payment card fits that role well:

• It is standardized to a fraction of a millimeter and widely available.
• It is rigid and flat, so it can be pressed against a screen without bending.
• Its long edge, 85.60 mm, is long enough that a small alignment slip has a small relative effect: 0.5 mm off is about 0.6 percent.
• It has straight edges and rounded corners, so the edge itself is easy to align with an on-screen outline.

The calibration itself is simple arithmetic. If the on-screen outline is w CSS pixels wide when it matches the card, then the display shows w × 25.4 / 85.60 CSS pixels per inch, and the screen ruler uses that value to place every tick. The methodology page walks through the same calculation in more detail.

Using a card to check a ruler

On-screen ruler. Open the millimeter ruler, set browser zoom to 100 percent (Ctrl/Cmd+0), and hold a card flat against the glass with its left edge at zero. The right edge should sit at 85.6 mm. On the inch view, it should fall just under the 3 3/8 mark (3.375 in), since 3.370 in is 0.005 in shorter. If it does not line up, recalibrate; the accuracy page explains how the remaining error is estimated after calibration.

Physical ruler or tape. Lay the card along the scale. A properly graduated metric ruler reads 85.5 to 86 mm across the card. A reading far from that usually means the zero mark has worn away or the ruler is a cheap print with inconsistent spacing.

Printed document scale. When a drawing, pattern, or template is supposed to be printed at 100 percent, place a card on the paper next to any dimension you know, such as a 10 cm scale bar or a labeled 3-inch part. If the printed 10 cm bar is longer than the card by roughly 14.4 mm (100 − 85.6), the print is at scale. If the bar is shorter than the card, the printer shrank the page, most often because "fit to page" was left on.

Photographs. A card placed in the same plane as the object you want to measure gives a photo a known scale. Marking its long edge as 85.6 mm in the image measurement tool sets pixels per millimeter for everything else lying flat beside it.

Converting card dimensions

Any card measurement can be moved between units with the unit converter, but the core figures are worth memorizing: 85.60 mm is approximately 3.370 in, and 53.98 mm is approximately 2.125 in. Ten cards stacked are 7.6 mm tall. Twelve cards laid end to end along their long edges span 1027.2 mm, a little over one meter, which makes a card a serviceable improvised measuring stick when nothing else is at hand.