It's about one-three-hundred-fifty-thousandth as tall as The Challenger Deep (Marianas Trench).
In other words, 3 centimeters is 0.00000275180 times the height of The Challenger Deep (Marianas Trench), and the height of The Challenger Deep (Marianas Trench) is 363,400 times that amount.(near Marianas Islands, a.k.a. Ladrones Islands, northwestern Pacific Ocean) (depth below sea level)
The Challenger Deep, at the southern end of the Marianas Trench, reaches a depth of 1,090,200 centimeters below sea level. There has been only one manned expedition to the bottom of Challenger Deep — a 1960 voyage that took 4 hours and 48 minutes to reach the bottom.
It's about one-three-hundred-fifty-thousandth as tall as Maxwell Montes.
In other words, the height of Maxwell Montes is 370,000 times 3 centimeters.(Ishtar Terra, Venus)
Maxwell Montes rises to a total height of 1,100,000 centimeters. Since Venus does not seem to have the kind of tectonic activity which gives rise to mountains on Earth, the origin of the Venusian mountain remains the subject of some dispute.
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.