Gallons to Pounds Converter

Only for water, and only roughly. A US pint of water weighs about 1.043 lb (8.345 lb/gal divided by 8 pints), so the rhyme is off by about 4 percent on the US side, close enough for a backyard estimate but wrong for any serious measurement. For UK pints the rhyme breaks badly: a UK Imperial pint is 568 mL (20 UK fl oz), so a UK pint of water weighs about 1.253 lb, 25 percent over a pound. The rhyme is also wrong for almost every liquid that isn't water. A US pint of gasoline weighs about 0.77 lb, a US pint of honey weighs about 1.48 lb, and a US pint of olive oil weighs about 0.96 lb. Use the rhyme to remember that water is roughly a pound per pint; use this calculator for anything else.

They are different volumes. A US liquid gallon is 3,785.411784 mL, while an Imperial gallon is 4,546.09 mL. The Imperial gallon is about 20.1 percent larger, so the same liquid weighs more per Imperial gallon. Multiply US gallons by about 0.83267 to get the equivalent number of Imperial gallons, or multiply Imperial gallons by about 1.20095 to get US gallons.

About 16.4 percent of volume. The US liquid gallon is 3,785.41 mL (231 cubic inches) and is used for fuel, water, milk, and every other liquid sold by the gallon in the US. The US dry gallon is 4,404.88 mL (268.8025 cubic inches), about a sixth larger, and survives almost entirely as a definition under the US dry quart and dry pint, which the USDA still uses for grain, fruit, and produce sold by volume rather than by weight. A dry pint of strawberries (550 mL) is bigger than a liquid pint of milk (473 mL) because of this split. For weighing liquids the US liquid gallon is almost always the right choice; the dry gallon is included here for completeness when a recipe or USDA specification calls for it.

Because gasoline blends change between summer and winter, and density changes with them. EPA-mandated summer-blend gasoline (sold roughly June through mid-September in most US regions) uses heavier hydrocarbons with a lower Reid vapor pressure to cut evaporative smog emissions, and it typically runs near 0.74 to 0.77 g/mL, or about 6.18 to 6.43 lb per US gallon. Winter-blend gasoline (mid-September through May) shifts toward lighter, more volatile components like butane to help cold-weather starting, dropping the density to roughly 0.71 to 0.74 g/mL, or 5.93 to 6.18 lb per US gallon. On top of that, gasoline expands about 0.06 percent per degree Fahrenheit, so a tank loaded on a 95 F afternoon weighs slightly less per gallon than the same tank loaded on a 35 F morning. For ballpark airplane and cargo weight-and-balance work, pilots use 6.0 lb per US gallon for avgas; for a sedan, the swing is rarely more than a pound or two on a full tank, but it shows up in long-haul trucking and aviation manifests.

Because its atoms are heavier and packed more tightly. Mercury (chemical symbol Hg) has an atomic mass of 200.6 atomic mass units against water's molecular mass of 18.0, so each mercury atom is more than 11 times heavier than a water molecule. Mercury atoms also pack into a metallic liquid lattice that is denser per unit volume than water's hydrogen-bonded molecular network, which finishes the 13.534 g/mL figure (against water's 1.0 g/mL at 4 C). The practical consequence is that a single US gallon of mercury weighs 112.95 lb, the same as a large dog or a small adult, which is why old barometers, manometers, and thermometers used surprisingly small amounts of mercury to balance large atmospheric pressures. A 760 mm column of mercury balances one standard atmosphere of pressure (14.696 psi) in a tube under 1 cm wide because that column is so heavy for its volume. Mercury is also why every other density is usually quoted in g/mL or g/cm cubed relative to water: water is the convenient unit reference, and mercury is the dramatic upper end of the everyday density scale.