
It's about half as big as a Postit® Note (3M).
In other words, 2,640 square millimeters is 0.49 times the size of a Postit® Note (3M), and the size of a Postit® Note (3M) is 2 times that amount.
(3M) (generically sticky notes, a.k.a. repositionable notes, a.k.a. repositional notes)A Postit® Note measures 5,400 square millimeters in total area. In September, 1989, Hurricane Hugo swept through Charleston, South Carolina with winds up to 230 kph (140 mph), uprooting eight oak trees in Mr. Bruce Brakefield's yard, but leaving in place a Postit® note attached to his front door.
It's about half as big as a Playing Card.
In other words, 2,640 square millimeters is 0.47 times the size of a Playing Card, and the size of a Playing Card is 2.1 times that amount.
(ISO 216 B8 size)A single ISO 216 B8size playing card measures 5,600 square millimeters. Although this size is the most common playing card, many casinos use the smaller "bridge size" card — 2,604 sq. mm smaller.
It's about threeandahalf times as big as a Secure Digital (SD) card.
In other words, the size of a Secure Digital (SD) card is 0.29 times 2,640 square millimeters.
A Secure Digital (SD) card measures 3.2 cm by 2.4 cm for a total area of 770 square millimeters. SDXC Cards, the latest standard for the technology, will allow the cards to hold up to 2 terabytes of data.
It's about fiveandahalf times as big as a Quarter.
In other words, 2,640 square millimeters is 5.712 times the size of a Quarter, and the size of a Quarter is 0.1751 times that amount.
(United States quarterdollar coin) (a.k.a. Quarter dollar, a.k.a. Washington quarter, a.k.a. two bits)The George Washington quarter, in circulation in various forms since 1932, has a diameter of 24.26 mm (0.955 in) and an area of 462.2 sq. mm.
It's about seven times as big as a Postage Stamp.
In other words, the size of a Postage Stamp is 0.1 times 2,640 square millimeters.
(average; United States dimensions)A typical postage stamp measures an average of 400 sq. mm. One of the most prized stamps among collectors is the USissued "Inverted Jenny" stamp printed in 1918, which features an upsidedown image of Curtiss JN4 ("Jenny") airplane; a single stamp sold for $977,500 at a 2007 auction.
It's about sevenandahalf times as big as a Nickel.
In other words, 2,640 square millimeters is 7.472 times the size of a Nickel, and the size of a Nickel is 0.1338 times that amount.
(United States fivecent coin) (a.k.a. Jefferson nickel)The nickel, in its current design since 1938, has a diameter of 21.21 mm (0.835 in) and an area of 353.3 sq. mm.
It's about nineandahalf times as big as a Penny.
In other words, 2,640 square millimeters is 9.26 times the size of a Penny, and the size of a Penny is 0.108 times that amount.
(United States onecent coin) (a.k.a. Lincoln penny, a.k.a. Cent, a.k.a. One cent piece)The Lincoln penny, in its current design since 1909, has a diameter of 19.05 mm (0.75 in) and an area of 285.0 sq. mm. 
