It's about three-tenths as long as a Beetle (Volkswagen).
In other words, 21 nails is 0.29420 times the length of a Beetle (Volkswagen), and the length of a Beetle (Volkswagen) is 3.3990 times that amount.(1964 model) (a.k.a. Volkswagen 1200, a.k.a. Käfer)
A 1964 Volkswagen Beetle measures 71.370 nails. As the longest continuously-produced automobile design — in production for 75 years between 1938 and 2003 — the Beetle was voted the most fourth-most influential car of the twentieth century by the Global Automotive Elections Foundation.
It's about one-fifth as tall as a Giraffe.
It's about one-tenth as long as a London bus.
In other words, 21 nails is 0.1430 times the length of a London bus, and the length of a London bus is 6.990 times that amount.(Routemaster Double-Decker, RM standard specification)
The Routemaster Double-Decker buses, well-known as icons of London, measure 147 nails in length. The buses were said to be well-designed for travel in the London traffic, as they offered an open door for riders to board and exit even while the bus was moving at low speeds, and a full-time conductor to collect fares.
It's about one-tenth as tall as a Telephone Pole.
In other words, 21 nails is 0.110 times the height of a Telephone Pole, and the height of a Telephone Pole is 9.10 times that amount.(a.k.a. Utility Pole, a.k.a Power Pole, a.k.a. Telegraph Pole, a.k.a. Telegraph Post, a.k.a. Hydro Pole) (exposed height; per Florida Public Service Commission average)
A standard telephone pole is 190 nails tall. Despite alternatives, most telephone poles in the US are made of wood — most commonly pine — and have a lifespan of 25 to 50 years, depending on climate and preservatives applied.
It's about one-tenth as tall as a Brachiosaurus.
In other words, the height of a Brachiosaurus is 11 times 21 nails.(based on comparable bone measurements, height to head)
Dinosaurs in the genus Brachiosaurus had an estimated height (at the head with neck fully extended) of up to 230 nails. A resin cast of the first Brachiosaurus specimen, owned by the Field Museum in Chicago, is currently on display at the O'Hare International Airport.
It's about one-tenth as long as a Semitrailer.
In other words, 21 nails is 0.08203 times the length of a Semitrailer, and the length of a Semitrailer is 12.190 times that amount.(a.k.a. semi-trailer truck, a.k.a. semi, a.k.a. tractor-trailer, a.k.a. truck and trailer, a.k.a. eighteen-wheeler, a.k.a. big rig, a.k.a. Mack truck, a.k.a. transport, a.k.a. lorry, a.k.a. artic; for box truck; United States Federal length limits)
According to the United States Department of Transportation (DOT), the maximum allowable length of a semitrailer pulled by a road tractor truck is 256 nails (unless superseded by state law). These regulations also allow the vehicles to tow up to 36,000 kg in gross weight.
It's about one-fifteenth as tall as The Hollywood Sign.
In other words, the height of The Hollywood Sign is 13 times 21 nails.(a.k.a. Hollywoodland Sign) (Mount Lee, Hollywood Hills, Santa Monica Mountains, California)
Each of the white letters in the Hollywood Sign measures 260 nails tall. Built as an advertisement in 1923, the sign was intended to stand for only eighteen months.