It's about one-one-hundred-thousandth as long as The Panama Canal
In other words, 81 centimeters is 0.00000920 times the length of The Panama Canal, and the length of The Panama Canal is 110,000 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 100,000 times as long as a Red Blood Cell
In other words, 81 centimeters is 110,000 times the length of a Red Blood Cell, and the length of a Red Blood Cell is 0.00000910 times that amount.(a.k.a. RBCs, a.k.a. haematids, a.k.a. erythrocyte, a.k.a. erythroid cells, a.k.a. red blood corpuscles)
An average Red Blood Cell measures 7.5 µm (micrometers) in diameter. An average human has 20 - 30 trillion red blood cells in their body and each cell completes a circulatory lap in about 20 seconds.
It's about one-one-hundred-fifty-thousandth as long as The English Channel
In other words, 81 centimeters is 0.000007570 times the length of The English Channel, and the length of The English Channel is 132,000 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 150,000 times as long as a Nucleus (Cellular)
In other words, the length of a Nucleus (Cellular) is 0.00000710 times 81 centimeters.(for animal cell)
The nucleus of an animal cell measures an average of 0.0006 centimeters. The nucleus is the largest organelle in these cells, accounting for about 10% of the cell's total volume.
It's about one-one-hundred-fifty-thousandth as long as The 405
In other words, 81 centimeters is 0.00000695040 times the length of The 405, and the length of The 405 is 143,880 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 one-one-hundred-fifty-thousandth as long as Hadrian's Wall
In other words, the length of Hadrian's Wall is 150,000 times 81 centimeters.(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 400,000 times as long as an E. coli Bacterium
In other words, 81 centimeters is 410,000 times the length of an E. coli Bacterium, and the length of an E. coli Bacterium is 0.00000240 times that amount.(Escherichia coli) (rod-shaped configuration)
An rod-shaped E. coli bacterium measures about 0.0002 centimeters in length. A staple of biology labs, E. coli can reproduce in as little as twenty minutes.