It's about 0.000000000000000002 times as big as Earth's Oceans.
In other words, 494.1 gallons is 0.0000000000000000013 times the size of Earth's Oceans, and the size of Earth's Oceans is 770,000,000,000,000,000.0 times that amount.(Total water volume of Atlantic, Pacific, Indian, Arctic, and Southern Oceans) (estimated)
Over 97% of the Earth's water is found in the planet's five oceans for a total volume of about 370,000,000,000,000,000,000.0 gallons. The Pacific Ocean is the largest ocean, covering 165,760,000 sq. km — more than double the area of the Atlantic Ocean at 82,400,000 sq. km.
It's about 0.0000000000000008 times as big as The Gulf of Mexico.
In other words, 494.1 gallons is 0.0000000000000007684 times the size of The Gulf of Mexico, and the size of The Gulf of Mexico is 1,301,000,000,000,000.0 times that amount.(water volume)
The Gulf of Mexico contains 643,000,000,000,000,000.0 gallons of water. Every second, the Mississippi River empties 3,170,000 gallons of water into the Gulf.
It's about 0.0000000000005 times as big as The Grand Canyon.
In other words, 494.1 gallons is 0.000000000000449 times the size of The Grand Canyon, and the size of The Grand Canyon is 2,230,000,000,000 times that amount.(Coconino County and Mohave Counties, Arizona, near Fredonia and Grand Canyon, Arizona)
A dynamic and continuously changing landscape, the Grand Canyon has an approximate volume of 1,100,000,000,000,000.0 gallons. The strata of the rock visible in the Canyon's walls display nearly 2 billion years of geological history.
It's about 0.0000000000005 times as big as an Halley's Comet.
In other words, 494.1 gallons is 0.00000000000047 times the size of an Halley's Comet, and the size of an Halley's Comet is 2,100,000,000,000 times that amount.(Comet Halley, officially "1P/Halley") (volume calculated based on 2005 dimensions)
Halley's Comet, the famous comet visible to observers on Earth approximately every 76 years, has a peanut- or potato-shaped nucleus made of rock, dust, ice, and various frozen gasses. The nucleus measures approximately 15 km by 8 km by 8 km, which yields a calculated volume of 1,100,000,000,000,000.0 gallons. The coma of the Comet — the trail of sublimated gasses that give the Comet its visibility — may be up to 100,000 km in length.
It's about 0.000000004 times as big as Sydney Harbour.
In other words, 494.1 gallons is 0.00000000333 times the size of Sydney Harbour, and the size of Sydney Harbour is 300,000,000 times that amount.(formally Port Jackson, a.k.a. Sydney Harbor) (Sydney, New South Wales, Australia) (total estuary water volume at high tide)
Lending the term "sydharb" or "sydarb" to comparable quantities of water, Sydney Harbor contains approximately 148,000,000,000 gallons of water. Snapper Island, a onetime naval facility loocated in the Harbour, was transformed by the dredging efforts of the Australian Navy from a 2,360 sq. m (25,400 sq. ft) outcropping to a 16,500 sq. m (178,000 sq. ft) island shaped roughly in the outline of a boat.
It's about 0.0000008 times as big as The Great Pyramid of Giza.
In other words, 494.1 gallons is 0.0000007704569 times the size of The Great Pyramid of Giza, and the size of The Great Pyramid of Giza is 1,297,931 times that amount.(a.k.a. Pyramid of Khufu, a.k.a. Pyramid of Cheops) (Cairo, Egypt) (including internal hillock)
The Great Pyramid of Giza has an estimated volume of 641,307,800 gallons including its internal hillock. The 2,300,000 stones used in the construction of the pyramid weighed an average 2.27 metric tons (2.06 short tons) and were quarried at distances of up to 805 km (500 mi) away.
It's about one-nine-hundred-thousandth as big as The Melbourne Cricket Ground.
In other words, 494.1 gallons is 0.0000011 times the size of The Melbourne Cricket Ground, and the size of The Melbourne Cricket Ground is 910,000 times that amount.(a.k.a. MCG, a.k.a. "The G") (Yarra Park, melbourne, Victoria, Australia) (internal volume)
The MCG has an internal volume of approximately 450,000,000 gallons. The first cricket game held on the site of the MCG was in 1853 when the Melbourne Cricket Club was granted permission to a roughly 0.04 sq. km (10-acre) area to be used "for cricket and no other purpose."