It's about three-fifths as big as a Hot Tub.
In other words, 421 liters is 0.5860 times the size of a Hot Tub, and the size of a Hot Tub is 1.710 times that amount.(for Lifesmart Rock Solid Simplicity Plug and Play 4 Person Spa With 12 Jets) (a.k.a. Spa, a.k.a. Jacuzzi, a.k.a. Whirlpool) (Advertised Capacity)
An average, four-person hot tub holds 719 liters of water. Modern hot tubs became popular outside of Japan starting in about 1940.
It's about two-and-a-half times as big as a Bathtub.
In other words, the size of a Bathtub is 0.380 times 421 liters.(a.k.a. bath, a.k.a. tub) (for Bootz Industries Aloha 5 ft. Left Hand Drain Soaking Tub)
The capacity of a typical bathtub is 160 L. Historically, bathtubs have been made of various materials including marble, terracotta, silver, gold, and iron but the size and shape of the tubs has changed little in their 7,000 year history.
It's about five-and-a-half times as big as a Car Gas Tank.
In other words, 421 liters is 5.560 times the size of a Car Gas Tank, and the size of a Car Gas Tank is 0.180 times that amount.(for 2009 Ford Taurus)
A car gas tank (for example, that of a 2009 Ford Taurus) holds 75.7 L of gas. In contrast, the Curved Dash Oldsmobile — the first mass-produced car — had a fuel capacity of just 20 L.
It's about seven times as big as a Beer Keg.
In other words, 421 liters is 7.170 times the size of a Beer Keg, and the size of a Beer Keg is 0.1390 times that amount.(Half barrel; maximum capacity)
The most common keg size sold by US beer sellers is a half-barrel type with a volume of 58.7 L. This type of keg contains the equivalent of 165 0.35488 L cans of beer.
It's about one-twenty-fifth as big as a Concrete Mixer Truck.
In other words, the size of a Concrete Mixer Truck is 26 times 421 liters.(a.k.a. cement mixer, a.k.a. cement mixer truck, a.k.a. cement transport truck, a.k.a. concrete mixer, a.k.a. concrete transport truck, a.k.a. in-transit mixer)(standard size; drum capacity)
A concrete mixer truck has a drum volume of up to 11,000 liters. Concrete mixer trucks can be in transit for about 90 minutes before the concrete dries — if the concrete dries while in the drum, jackhammers or even dynamite must be used to remove it.
It's about forty times as big as a Basketball (packed).
In other words, 421 liters is 37.9267708570 times the size of a Basketball (packed), and the size of a Basketball (packed) is 0.026366600093 times that amount.(64% packing density) (NBA official ball standards, Size 7)
A NBA official ball, manufactured by Spalding, is a Size 7 ball measures about 7.10421672870 liters. These balls have 4,118 pebbles each with a diameter of 2.5 mm
It's about 50 times as big as a Bowling Ball (packed).
In other words, 421 liters is 51.1335000060 times the size of a Bowling Ball (packed), and the size of a Bowling Ball (packed) is 0.019556650726 times that amount.(64% packing density) (USBC specifications; tenpin)
According to United States Bowling Congress specifications, a tenpin bowling ball should measure at least 10.795 cm (4.25 in) in radius for a total volume of about 5.26934397150 liters. Because regulation balls measure the same diameter irrespective of their weight, ball density varies by size and balls weighing less than about 5 kg (11 lbs) will float in water.