Credit card size, and the other objects you can measure with

How big is a credit card?

85.60 mm long by 53.98 mm high, with rounded corners. Debit and credit cards, most national ID cards and driving licenses, hotel key cards and the majority of gift and loyalty cards are the same rectangle: the ID-1 format of ISO/IEC 7810, the international standard for identification cards. The dimensions are given to hundredths of a millimeter because cash machines, card readers and passport gates all have to accept a card cut on another continent a decade earlier.

The standard is metric. In other units:

• Millimeters: 85.60 × 53.98 mm
• Centimeters: 8.560 × 5.398 cm, or 8.6 × 5.4 cm for anything you would do with a tape measure
• Inches: 3.370 × 2.125 in
• In fractions: 2 ¹⁄₈ in is 2.125 in, so the short edge lands on a tape-measure mark to within two ten-thousandths of an inch. The long edge falls between marks: 3 ³⁄₈ in is 3.375 in, five thousandths of an inch longer than the card.

An inch is defined as exactly 25.4 mm, so the conversions are exact, and the table rounds them to three decimal places. The physical card can vary a little, and the next section gives the limits.

How much a card may vary

85.60 mm is the nominal size. The standard also publishes the limits a card has to stay inside. For a card in a wallet, the row that applies is the one for personalized and returned cards in Figure 1 of ISO/IEC 7810:2019. The standard's own definition of an unused card excludes anything that has been through a personalization step, and every bank card, ID card and license has been printed, embossed or encoded. That row is 85.37 to 85.90 mm across and 53.82 to 54.18 mm high.

The limits sit unevenly around the nominal size, so the band uses the larger of the two excursions: 0.30 mm over 85.60 mm is 0.351% on the long edge, and 0.20 mm over 53.98 mm is 0.371% on the short one. Lining two edges up by eye is the bigger term in a screen calibration. The site takes it as 0.7 mm across the pair, which is 0.818% of the long edge, a little over twice the card's own contribution. The card's share is smaller but still counts, and the two add up, which is why the ruler prints ±1.2% beside a long-edge match and ±1.7% beside a short-edge one.

Two effects fall outside those percentages, and no band covers them. A card that has spent two years bowing in a back pocket presents a shortened width, and nothing on a screen can see that it is bent. And the standard's limits are defined at 23 °C ± 3 °C and 40–60% relative humidity, so a card measured on a car dashboard in August is outside the conditions those limits assume.

Every object this site carries, in millimeters, centimeters and inches

The table lists sixteen objects, and this site offers two of them as references. An object can have a perfectly good published size and still be a bad thing to hand a beginner, and the reason for each one not offered is printed in full, as it is recorded in the site's data.

The euro notes get one row per denomination because their sizes differ: a €5 is 120 × 62 mm and a €50 is 140 × 77, so a single "euro note" row would be a wrong number for five of the six. US Letter has no tolerance in the table because the standards that define its size do not give one. ASME Y14.1 fixes the 8.5 × 11 inch sheet and says nothing about how far a real sheet may stray, and the cut-size office paper specification that once did was withdrawn in 2014 without replacement. For a paper check the site uses A4, whose 297 mm long edge makes it the better choice.

Measuring without a ruler, and what each object is good for

Pick the longest rigid object you have, even over a shorter, more precise one. Your hand-and-eye error when you line an edge up is roughly fixed at a fraction of a millimeter, so the longer the object, the smaller the share of it that error takes. The same 0.7 mm of slop is 0.236% of an A4 sheet's long edge, 0.449% of a dollar bill's, 0.818% of a card's long edge and 2.9% of a US quarter's diameter.

For inches, the neatest object in the table is the US penny. At 19.05 mm it is 0.750 in, three quarters of an inch with no rounding at all, and four of them in a row make three inches. A quarter is 24.26 mm, which is 0.955 in, so it is 4.5% short of an inch and is the wrong object to guess with. The card's short edge at 2.125 in is the closest thing to a ruled length most people carry: two of them, butted end to end, are 4.250 in.

For centimeters, a card is 8.560 cm by 5.398 cm, which makes it a decent stand-in for an 8.5 cm line and a poor one for a 5 cm line. A US banknote is 15.596 cm long whatever the denomination. For millimeters, a dime is 17.91 mm and a nickel 21.21 mm. The two coins are close in size, so check which one you are holding before you trust either number.

The coin and banknote figures are nominal dimensions. This site has not read a mint or central-bank tolerance from a source it can cite for any of them, so it publishes each size and does not calibrate from the object, and the table says so on every row.

References to avoid

Do not calibrate from body parts. "My thumb is about an inch" and "this knuckle is two centimeters" are fine for guessing whether a shelf will fit. Body dimensions vary between people and your memory of them drifts, so for calibrating an instrument the error is unknown and unbounded, and you would never find out it was there.

Do not hold a tape measure to the glass either. Cloth tapes stretch, steel ones bow away from a vertical screen, and the hook on the end is built to catch a board edge and does not sit flush on a flat pane.

Avoid any object you might mix up with another, because that error has no band. An older-style national ID card is 105 × 74 mm and its own tolerance is better than a bank card's: it would print ±1.0% where a bank card prints ±1.2%. The site still refuses it, because a bank card and an older ID card are both "a card from my wallet". Pick the wrong one and the calibration is 105/85.6 = 22.7% wrong with every signal on the page identical: a green state, a tight band, a plausible pixel density. A tolerance error is bounded by the number printed next to it. A mix-up is bounded by nothing, and a tight band printed over a 23% error is worse than no row at all. The mini-SIM row is withheld for the same reason: the object most people are holding is a nano-SIM, which the standard does not define at all, and that mix-up is 103% wrong.

What to do with a reference once you have one

On a screen, a known length converts pixels into millimeters. Use a clean, flat, undamaged, smooth-edged card and hold it just above the display without touching it; do not press or slide it on the glass. Drag the ruler's outline until the edges agree, and the page divides the matched width by 85.60 to learn how many pixels your display puts in a millimeter. No browser can know that number on its own, which is why an uncalibrated on-screen ruler is typically 25 to 40 percent short. The screen calibration guide explains where that error comes from.

Three habits close most of the remaining gap. Match the card's physical edges and ignore its printed artwork, because the standard fixes the size of the blank card and says nothing about the printing. Look square-on and keep the gap as small as practical without contact; any gap or tilt is outside the printed error band. Use the longest edge that fits: on a phone in portrait an 85.60 mm edge will not go across a 64 mm display, so hold the card upright just above it and keep the long edge, whose band is narrower than the short edge's. For hard, sharp or abrasive objects, skip the screen and use the printable ruler or another physical ruler.

The figures on this page were read from the site's reference data on 2026-08-09. Each row says whether its tolerance has been verified, and the two offered rows give the verification date.