About

Volume conversions between cubic feet and gallons are a frequent source of costly errors in plumbing, pool construction, HVAC sizing, and agricultural irrigation. A single wrong factor can oversize a pump by 20% or underestimate a tank's capacity by dozens of gallons. The problem is compounded by the existence of three distinct gallon definitions: the US Liquid gallon (3.785411784 L), the US Dry gallon (4.40488377086 L), and the Imperial gallon (4.54609 L). Confusing them introduces errors exceeding 20%. This converter applies the exact NIST-traceable factors derived from the definition of one cubic foot as exactly 28.316846592 L.

Limitations: the tool assumes standard conditions and does not account for thermal expansion of liquids. For precision metering of fuels or chemicals at non-ambient temperatures, apply a volume correction factor per ASTM D1250. Pro tip: US construction and pool industries use the US Liquid gallon exclusively. If you encounter "gallons" in a British or Canadian specification, assume Imperial gallons unless stated otherwise.

Formulas

The conversion relies on the ratio of one cubic foot expressed in liters to the liter-definition of each gallon type.

V_gal = V_ft³ × 28.316846592k

Where k is the gallon definition in liters:

k_{US Liq} = 3.785411784 L ⇒ 1 ft³ = 7.48051948 gal

k_{US Dry} = 4.40488377086 L ⇒ 1 ft³ = 6.42851 dry gal

k_Imperial = 4.54609 L ⇒ 1 ft³ = 6.22883 imp gal

For the reverse conversion:

V_ft³ = V_gal × k28.316846592

Where V_gal = volume in gallons, V_ft³ = volume in cubic feet, k = gallon-to-liter constant for the selected gallon type. All factors are exact per NIST SP 811 definitions.

Reference Data

Cubic Feet (ft³)	US Liquid Gallons (gal)	US Dry Gallons (dry gal)	Imperial Gallons (imp gal)	Liters (L)
0.1	0.7481	0.6429	0.6229	2.8317
0.25	1.8701	1.6071	1.5572	7.0792
0.5	3.7403	3.2143	3.1144	14.1584
1	7.4805	6.4285	6.2288	28.3168
2	14.9610	12.8570	12.4577	56.6337
5	37.4026	32.1426	31.1442	141.5842
10	74.8052	64.2851	62.2883	283.1685
15	112.2078	96.4277	93.4325	424.7527
20	149.6104	128.5703	124.5767	566.3369
25	187.0130	160.7128	155.7209	707.9212
50	374.0260	321.4257	311.4417	1415.8423
75	561.0389	482.1385	467.1626	2123.7635
100	748.0519	642.8514	622.8835	2831.6847
200	1496.1039	1285.7027	1245.7669	5663.3693
500	3740.2597	3214.2568	3114.4173	14158.4233
1000	7480.5195	6428.5135	6228.8346	28316.8466
1337 (avg pool)	10,003.5	8,594.9	8,327.9	37,867.4
2000	14,961.0	12,857.0	12,457.7	56,633.7
5000	37,402.6	32,142.6	31,144.2	141,584.2

Frequently Asked Questions

The US Liquid gallon equals exactly 3.785411784 L and is used for beverages, fuel, and pool volumes. The US Dry gallon equals 4.40488377086 L and appears in grain and produce measurement. The Imperial gallon, used in the UK and some Commonwealth countries, equals exactly 4.54609 L. The Imperial gallon is roughly 20% larger than the US Liquid gallon. Using the wrong type when sizing a tank or ordering fuel can cause significant overfill or shortfall.

The commonly cited 7.5 is a rounded approximation. The exact value is 7.48051948 US Liquid gallons per cubic foot, derived from 28.316846592 L ÷ 3.785411784 L. Over large volumes the rounding error compounds. For a 1000 ft³ tank, using 7.5 instead of 7.48052 overstates capacity by about 19.5 gallons.

Use V = π × r² × h, where r is the radius in feet and h is the height in feet. A tank with diameter 4 ft and height 6 ft yields π × 2² × 6 ≈ 75.398 ft³. Enter that result into this converter to get gallons.

The geometric conversion factor itself is a fixed mathematical ratio and does not change with temperature. However, the actual volume of a liquid expands with heat. Water at 60 °F (15.6 °C) is the reference temperature for US petroleum gallon measurements per API/ASTM standards. At 100 °F, water occupies roughly 1.2% more volume. For custody-transfer accuracy of fuels, apply ASTM D1250 Volume Correction Factors after conversion.

A typical rectangular residential pool measuring 12 × 24 ft with an average depth of 5 ft has a volume of 1440 ft³, which equals approximately 10,772 US Liquid gallons. Pool chemical dosing charts assume US Liquid gallons. Using Imperial gallons would result in under-dosing chlorine by about 17%.

You can convert the numerical volume, but the result represents a geometric equivalence only. Natural gas is sold in standard cubic feet (SCF) measured at 60 °F and 14.696 psia. Converting SCF to liquid gallons requires knowing the gas's compressibility factor and condensation properties, which is a thermodynamic calculation beyond a simple unit conversion.