It's about as big as a Hot Tub
(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 6.220 barrels of water. Modern hot tubs became popular outside of Japan starting in about 1940.
It's about four-and-a-half times as big as a Bathtub
In other words, the size of a Bathtub is 0.220 times 6.220 barrels.(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 1.40 barrels. 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 nine-and-a-half times as big as a Car Gas Tank
It's about twelve-and-a-half times as big as a Beer Keg
It's about one-fifteenth as big as a Concrete Mixer Truck
In other words, the size of a Concrete Mixer Truck is 15 times 6.220 barrels.(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 95 barrels. 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 65 times as big as a Basketball (packed)
In other words, 6.220 barrels is 64.7914825910 times the size of a Basketball (packed), and the size of a Basketball (packed) is 0.01543412745 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 0.061440174551 barrels. These balls have 4,118 pebbles each with a diameter of 2.5 mm
It's about 85 times as big as a Bowling Ball (packed)
In other words, 6.220 barrels is 87.3529488690 times the size of a Bowling Ball (packed), and the size of a Bowling Ball (packed) is 0.01144781044 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 0.045571443798 barrels. 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.