Cubic Feet to Gallons Converter

Because the US gallon is defined by statute as exactly 231 cubic inches, and 1 cubic foot is exactly 1,728 cubic inches (12 in x 12 in x 12 in). The conversion is the exact ratio 1728 / 231 = 7.480519480519... US gallons per cubic foot, which rounds to 7.4805. There is no measurement involved, so the factor never drifts. The 231 cu in figure comes from the old Queen Anne wine gallon (1707), which Congress carried over into US measure in 1832 and Mendenhall's NIST predecessors never changed.

An imperial (UK) gallon holds about 20 percent more liquid than a US gallon. 1 imp gal equals 4.54609 liters exactly (UK Weights and Measures Act 1985), while 1 US gal equals 3.785411784 liters exactly (NIST since 1893). So 1 imp gal is about 1.20095 US gal. That is why a US car rated at 30 mpg becomes about 36 mpg in UK fuel-economy terms even though nothing about the car changed. For cubic feet, 1 cu ft = 7.4805 US gal but only 6.2288 imp gal. Always check which gallon a recipe, fuel-economy figure, or tank-spec sheet means before doing the math.

Compute the volume in cubic feet (length x width x average depth in feet), then multiply by 7.4805 to get US gallons. A typical 16 ft by 32 ft rectangular pool at an average depth of 5 ft is 16 x 32 x 5 = 2,560 cu ft, which is 2,560 x 7.4805 = 19,150 US gallons. Going the other way: a 5,000 US gal hot tub or plunge pool holds 5,000 / 7.4805 = 668 cu ft. For oval or kidney-shaped pools, calculate length x width x average depth x 0.85 (the kidney-shape factor) before multiplying by 7.4805. Always use average depth (shallow end plus deep end divided by two), not deep-end depth.

Because the US HVAC industry standardized on cubic feet per minute (CFM) for airflow in the early 20th century and has never switched. Ductwork, blower motors, exhaust fans, and dust-collection systems are all sized in CFM in ASHRAE standards. A typical bathroom exhaust fan moves 50 to 110 CFM; a kitchen range hood moves 300 to 600 CFM; a central air conditioner moves 400 CFM per ton of cooling capacity. Knowing the cu-ft-to-gallons conversion is useful for sizing humidifier reservoirs and condensate-line capacity, since 1 cu ft of air at typical indoor conditions holds only about 0.012 gallons of water, but a 4-ton AC running 8 hours removes roughly 5 to 10 gallons of condensate from the air.

Exactly 28.316846592 liters, which rounds to 28.32 L. The factor comes from the exact 1959 international foot definition (1 ft = 0.3048 m), so 1 cu ft = 0.3048 cubed = 0.028316846592 cubic meters, and 1 cu m = 1,000 L by SI definition. A 1 cu ft bag of compost or potting mix holds about 28.3 liters; a 2 cu ft bag of mulch (the standard US size) holds 56.6 L. For larger volumes, 1 cu yd = 27 cu ft = 764.55 L = 201.97 US gal, so a single cubic yard of landscaping material is just over 200 US gallons of equivalent volume.