
It's about as big as a Postit® Note (3M).
(3M) (generically sticky notes, a.k.a. repositionable notes, a.k.a. repositional notes)
A Postit® Note measures 8.40 square inches 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 as big as a Playing Card.
In other words, the size of a Playing Card is 1 times 8.40 square inches.
(ISO 216 B8 size)A single ISO 216 B8size playing card measures 8.70 square inches. Although this size is the most common playing card, many casinos use the smaller "bridge size" card — 4.10 square inches smaller.
It's about seven times as big as a Secure Digital (SD) card.
In other words, the size of a Secure Digital (SD) card is 0.140 times 8.40 square inches.
A Secure Digital (SD) card measures 3.2 cm by 2.4 cm for a total area of 1.20 square inches. SDXC Cards, the latest standard for the technology, will allow the cards to hold up to 2 terabytes of data.
It's about onetenth as big as an Apple iPad.
In other words, 8.40 square inches is 0.13540 times the size of an Apple iPad, and the size of an Apple iPad is 7.3860 times that amount.
(for 9.7 inch, Apple iPad Air MD785LL/B)An Apple iPad measures 23 cm (9.4 in) x 17 cm (6.6 in) for a total device area of 62.03 square inches. The base model iPad Air features 16 GB of storage capacity.
It's about ten times as big as a Postage Stamp.
In other words, the size of a Postage Stamp is 0.10 times 8.40 square inches.
(average; United States dimensions)A typical postage stamp measures an average of 0.60 square inches. 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 elevenandahalf times as big as a Quarter.
In other words, 8.40 square inches is 11.730 times the size of a Quarter, and the size of a Quarter is 0.08525 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 0.71640 square inches.
It's about fifteenandahalf times as big as a Nickel.
In other words, 8.40 square inches is 15.340 times the size of a Nickel, and the size of a Nickel is 0.06519 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 0.54760 square inches. 
