It's about one-and-three-fifths times as big as a Hot Tub
In other words, 33 firkins is 1.56 times the size of a Hot Tub, and the size of a Hot Tub is 0.641 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 21.10 firkins of water. Modern hot tubs became popular outside of Japan starting in about 1940.
It's about seven times as big as a Bathtub
In other words, 33 firkins is 7 times the size of a Bathtub, and the size of a Bathtub is 0.14 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 4.70 firkins. 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 one-tenth as big as a Concrete Mixer Truck
In other words, 33 firkins is 0.1 times the size of a Concrete Mixer Truck, and the size of a Concrete Mixer Truck is 10 times that amount.(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 320 firkins. 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 fifteen times as big as a Car Gas Tank
In other words, 33 firkins is 14.9 times the size of a Car Gas Tank, and the size of a Car Gas Tank is 0.067 times that amount.(for 2009 Ford Taurus)
A car gas tank (for example, that of a 2009 Ford Taurus) holds 2.220 firkins of gas. In contrast, the Curved Dash Oldsmobile — the first mass-produced car — had a fuel capacity of just 0.5870 firkins.
It's about nineteen times as big as a Beer Keg
In other words, 33 firkins is 19.2 times the size of a Beer Keg, and the size of a Beer Keg is 0.052 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 1.720 firkins. This type of keg contains the equivalent of 165 0.0104 firkins cans of beer.
It's about 100 times as big as a Basketball (packed)
In other words, 33 firkins is 101.28225241 times the size of a Basketball (packed), and the size of a Basketball (packed) is 0.009873398115 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 0.208526168180 firkins. These balls have 4,118 pebbles each with a diameter of 2.5 mm
It's about 150 times as big as a Bowling Ball (packed)
In other words, 33 firkins is 136.55040851 times the size of a Bowling Ball (packed), and the size of a Bowling Ball (packed) is 0.007323302881 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 0.154668156840 firkins. 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.