It's about one-and-three-tenths times as long as an Aspirin.
In other words, the length of an Aspirin is 0.77 times 17.91 milimeters.(for up & up aspirin, 325mg, regular strength tablets) (a.k.a. acetylsalicylic acid, a.k.a. ASA)
It's about one-third as tall as a Golf Tee.
In other words, the height of a Golf Tee is 3 times 17.91 milimeters.The most common golf tee size and the length preferred for iron and most wood clubs is 54 milimeters tall. The tee did not come into common use until it was promoted by professional golfers Walter Hagen and Joe Kirkwood, as part of a marketing effort by the patent-holder of the well-known, "Reddy Tee."
It's about eleven times as long as a Strand of Spaghetti (thickness).
In other words, the length of a Strand of Spaghetti (thickness) is 0.091 times 17.91 milimeters.(average; restaurant and supermarket applications) (based on FMA Omcan Italian Made TR50 Counter Top Pasta Machine Extruder 13317)
It's about fourteen-and-a-half times as long as a Grain of Sand.
In other words, the length of a Grain of Sand is 0.0699 times 17.91 milimeters.(medium grain)
Composed mainly of quartz, mica, feldspar, or magnetite, a grain of sand measures an average of 1.25 mm. In 2007, a team of seven in Myrtle Beach created the world's tallest sandcastle, which measured 15,100 milimeters in height.
It's about one-twentieth as tall as a Bowling Pin.
In other words, the height of a Bowling Pin is 21.3 times 17.91 milimeters.(USBC specifications; tenpin)
It's about one-thirty-fifth as long as a Woman's Footstep.
In other words, the length of a Woman's Footstep is 37 times 17.91 milimeters.(for healthy, middle-aged woman of average height; single step length)
It's about one-forty-fifth as long as a Man's Footstep.
In other words, the length of a Man's Footstep is 43 times 17.91 milimeters.(for healthy, middle-aged man of average height; single step length)