It's about one-nine-hundred-thousandth as tall as Olympus Mons
In other words, 3 centimeters is 0.00000110 times the height of Olympus Mons, and the height of Olympus Mons is 910,000 times that amount.(a.k.a. Mount Olympus) (Mars)
The tallest mountain in the solar system, Olympus Mons rises to approximately 2,700,000 centimeters. The mountain has been known to astronomers since the nineteenth century because it is tall enough to rise above Mars' frequent dust storms.
It's about 0.0000004 times as long as The Panama Canal
In other words, 3 centimeters is 0.000000340 times the length of The Panama Canal, and the length of The Panama Canal is 2,900,000 times that amount.(Canal de Panamá) (Panama)
Connecting the Atlantic and Pacific Oceans across the Isthmus of Panama, the Canal measures 8,800,000 centimeters in length. Ships passing through the Canal are raised (and then lowered) 2,600 centimeters above sea level through the lock-and-dam system.
It's about 0.0000003 times as long as The English Channel
In other words, 3 centimeters is 0.000000280 times the length of The English Channel, and the length of The English Channel is 3,570,000 times that amount.(average width between Isle of Ushant and The Walde Lighthouse) (La Manche, Ärmelkanal, Mor Breizh, Mor Bretannek) (a.k.a. The Channel)
The English Channel measures between 10,700,000 centimeters, narrowing as it flows northeast. The world speed record for a Channel crossing by swimmer was set by Australian Trent Grimsey in 2012, with a time of 6 hours, 55 minutes.
It's about 0.0000003 times as long as The 405
In other words, 3 centimeters is 0.000000257420 times the length of The 405, and the length of The 405 is 3,884,700 times that amount.(a.k.a. I-405, Interstate 405, San DIego Freeway) (Southern California)
Running from Irvine to San Fernando, The 405 runs a total of 11,654,000 centimeters. The 405 is the most heavily-trafficed freeway in the United States, with an average speed as low as 8 kph during rush hours.
It's about 0.0000003 times as long as Hadrian's Wall
In other words, 3 centimeters is 0.000000250 times the length of Hadrian's Wall, and the length of Hadrian's Wall is 4,000,000 times that amount.(a.k.a. Roman Wall, a.k.a. The Wall, a.k.a. Vallo di Adriano, a.k.a. Vallum Aelium, a.k.a. Severus' Wall) (from North Tyneside, Tyne and Wear, England, United Kingdom to Cumbria, North West England, United Kingdom)
Hadrian's Wall, which crossed England form the North Sea to the Irish Sea during the time of Roman rule, measures 12,000,000 centimeters (about 79 Roman miles). Roman soldiers — at one time up to 10,000 of them — only occupied Great Britain for about 246 years after the wall was built, after which time the local Brits began to take residence the wall's garrisons.
It's about 0.00000007 times as long as The Grand Canyon
In other words, 3 centimeters is 0.00000006730 times the length of The Grand Canyon, and the length of The Grand Canyon is 14,900,000 times that amount.(a.k.a. Gran Cañón) (Arizona) (Colorado River miles measure)
The Grand Canyon has a total length of 44,600,000 centimeters along the course of the Colorado River at its bottom. Having opened in early 2007, the Grand Canyon Skywalk allows tourists to stand on a horseshoe-shaped glass walkway 110,000 centimeters above the floor of Granite Gorge.
It's about 20,000,000 times as long as a Glucose Molecule
In other words, the length of a Glucose Molecule is 0.0000000500 times 3 centimeters.(C6H12O6, a.k.a. grape sugar) (open chain form)
Am individual glucose molecule measures 0.000000150 centimeters in its open-chain form. Glucose is the most common fuel source of energy in human biology, with 3.75 kilocalories of energy per gram.