
It's about seventenths as big as a Bathtub.
In other words, 30 gallons is 0.710 times the size of a Bathtub, and the size of a Bathtub is 1.40 times that amount.
(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 42 gallons. 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 oneandahalf times as big as a Car Gas Tank.
In other words, the size of a Car Gas Tank is 0.6670 times 30 gallons.
(for 2009 Ford Taurus)A car gas tank (for example, that of a 2009 Ford Taurus) holds 20 gallons of gas. In contrast, the Curved Dash Oldsmobile — the first massproduced car — had a fuel capacity of just 5.280 gallons.
It's about oneandninetenths times as big as a Beer Keg.
In other words, 30 gallons is 1.930 times the size of a Beer Keg, and the size of a Beer Keg is 0.5180 times that amount.
(Half barrel; maximum capacity)The most common keg size sold by US beer sellers is a halfbarrel type with a volume of 15.50 gallons. This type of keg contains the equivalent of 165 0.0937 gallons cans of beer.
It's about onefifth as big as a Hot Tub.
In other words, 30 gallons is 0.1580 times the size of a Hot Tub, and the size of a Hot Tub is 6.330 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, fourperson hot tub holds 190 gallons of water. Modern hot tubs became popular outside of Japan starting in about 1940.
It's about ten times as big as a Basketball (packed).
In other words, 30 gallons is 10.2305305460 times the size of a Basketball (packed), and the size of a Basketball (packed) is 0.09774664134 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 1.87673551360 gallons. These balls have 4,118 pebbles each with a diameter of 2.5 mm
It's about fourteen times as big as a Bowling Ball (packed).
In other words, 30 gallons is 13.7929705570 times the size of a Bowling Ball (packed), and the size of a Bowling Ball (packed) is 0.072500698516 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 1.39201341150 gallons. 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.
It's about sixteen times as big as a Basketball.
In other words, 30 gallons is 15.9852039790 times the size of a Basketball, and the size of a Basketball is 0.062557850454 times that amount.
(NBA official ball standards, Size 7)A NBA official ball, manufactured by Spalding, is a Size 7 ball and measures about 1.87673551360 gallons. The surface of these balls have 4,118 pebbles with a diameter of 2.5 mm each. 
