20 cubic feet to gallons

Twenty cubic feet is 149.6104 US gallons

34,560 cubic inches, 231 to the gallon

Twenty cubic feet is 149.6104 US gallons. The one step route multiplies the volume by 7.48051948051948. The longer route goes through cubic inches and lands on the same figure: 20 x 1,728 = 34,560 cubic inches, and 34,560 / 231 = 149.6104. The second route works because a US gallon is 231 cubic inches by definition rather than by measurement, so the two methods cannot disagree.

Metric is just as tidy. A cubic foot is 28.316846592 liters, so 20 x 28.316846592 = 566.3369 liters. Those liters divide by 4.54609 to give 124.5767 imperial gallons, the gallon used in the UK and in older equipment manuals. NIST Special Publication 811, Appendix B lists the US gallon at 3.785412 liters beside the cubic foot, and the BIPM SI Brochure, 9th edition, 2019, fixes the inch at 25.4 millimeters exactly. That fixed inch is where the liter figure comes from.

Two more units show up with tanks and soil. A cubic yard is 27 cubic feet, so 20 / 27 = 0.7407 cubic yard. A US dry gallon is 268.8025 cubic inches, and 34,560 / 268.8025 = 128.5702 dry gallons, a unit printed on potting mix and grain but never on a water bill. Buying soil by the dry gallon and water by the liquid gallon is how one order ends up short.

Two reference points are worth carrying around. Twenty cubic feet is 2.72 drums of 55 gallons, and it is 0.7407 of a cubic yard. Both come back in the sections below, because barrels and bulk loads are how this volume reaches a driveway.

Two 55 gallon drums, and a third one two thirds full

Barrels, totes and cans in the same volume

A 55 gallon drum holds 55 / 7.48051948051948 = 7.3524 cubic feet. Twenty cubic feet is 149.6104 / 55 = 2.7202 drums, so a garage gets two full drums and a third one two thirds of the way up. Three drums would carry 165 gallons, which is 22.0573 cubic feet, so the headspace left in that third drum is 20 - 14.7049 = 5.2951 cubic feet, or 0.72 of its own volume.

Rain barrels use the same arithmetic at a friendlier size. A 50 gallon barrel is 6.6840 cubic feet, so twenty cubic feet is 2.9922 barrels, and three barrels come within a quart of the target. A 275 gallon IBC tote is 36.7622 cubic feet, and twenty cubic feet fills 0.544 of one, which is why a single tote on a pallet replaces five drums and saves the floor space they eat.

The last column is a shopping number, not a decimal to hand to a cashier. Jugs come in fives and cans in thirties, so 29.92 jugs is thirty jugs, and 2.72 drums is three drums with one left empty for a while. Rounding up to the next whole container is the difference between a plan that holds water and a second trip to the store in the rain.

Shape decides how the containers stack. Drums roll and need a cradle or a strap, totes are square and stack two high on a pallet, and jugs fit a shelf with a lip. Twenty cubic feet of storage is small enough to live in a corner and heavy enough that the corner should be concrete.

Twenty nine 5 gallon jugs is a six week reserve

Days of drinking water by household size

The Ready.gov build a kit checklist plans one gallon per person per day for drinking and basic sanitation. Twenty cubic feet is 149.6104 gallons, which is 29.92 jugs of the 5 gallon size, and 149.6104 / 4 = 37.40 days for a household of four. One person drawing on the same stock gets 149.61 days, and a household of six gets 24.94.

A jug of water weighs more than people expect. Five gallons is 41.65 pounds, so a thirty jug reserve is 1,250 pounds sitting in a garage, and lifting one jug from the floor to a shelf is a two hand job for most adults. Keep the daily use jug on the floor with a spigot and store the rest on the bottom shelf.

Rotate the stock on a schedule you will keep. Write the fill month on each jug with a marker, use the oldest first, and refill from the tap rather than buying bottled water for storage. Tap water already meets drinking standards, and a sealed food grade jug keeps it usable for six months to a year.

Thirty four bags of 80 pound concrete mix

Bag yield, load weight and slab depth

An 80 pound bag of concrete mix yields about 0.6 cubic feet, so 20 / 0.6 = 33.33 bags, and bags sell whole, which makes the order 34. That is 2,720 pounds on the cart, two trips in a half ton pickup or one trip with a trailer. A 60 pound bag yields about 0.45 cubic feet and stretches the same pour to 44.44 bags, so 45 bags at 2,700 pounds, which is no lighter and twice the lifting.

Depth decides the area a pour covers. At 4 inches thick, 20 x 12 / 4 = 60 square feet, which is a 6 by 10 foot pad or a walk 3 feet wide and 20 feet long. At 6 inches it covers 40 square feet, and at 2 inches, 120 square feet. Mix to the water listed on the bag: extra water makes a pour easier to spread and weaker every year after that.

Ready mix is priced by the cubic yard, and twenty cubic feet is 0.7407 of one. At $165 a yard that is $122.22 of concrete against $232.90 for 34 bags at $6.85 each. A short load fee at the plant can close that gap or open it wider, so the phone call decides a pour this small, not the arithmetic.

How much rain a 500 square foot roof sends to the barrels

One inch of rain, 311.7 gallons

Roof capture is where a twenty cubic foot reserve earns its place. An inch of rain on 500 square feet of roof is 500 / 12 = 41.6667 cubic feet, which is 311.6883 gallons. Twenty cubic feet of barrel holds 149.6104 gallons, or 0.48 of that inch, so a pair of drums catches just under half of a one inch storm and the downspout carries the rest away.

Scale the roof and the numbers move in a straight line. A 1,000 square foot roof sheds 623.3766 gallons per inch, and the same twenty cubic feet covers 0.24 of it. A 250 square foot shed roof sheds 155.8442 gallons, which is 0.96 of the storage, so one good storm nearly fills the barrels and a second one spills over the lid.

Divert the first rain. A screen on the downspout and a first flush diverter keep grit and shingle dust out of the barrel, and a tight lid with mesh stops mosquitoes from turning the stock into a nursery. Water off an asphalt roof is fine for beds, washing and the compost pile, and it needs treatment before anyone drinks it.

Height is free pressure. A barrel sitting 4 feet above the hose bib delivers about 1.7 pounds per square inch, enough for a soaker hose and not enough for a sprinkler. For anything more, a small transfer pump beats stacking barrels on a homemade tower.

1,247 pounds of water, and the floor under it

Weight per square foot and payload

Twenty cubic feet of water weighs 1,247.3 pounds at 62.366 pounds per cubic foot, the USGS Water Science School figure for water near 60 F. The gallon route reaches the same place: 149.6104 x 8.33 = 1,246.3 pounds. The one pound gap is rounding inside the density constant, not a different answer.

Spread the load and the floor gives its verdict. The same 1,247.3 pounds over a 3 by 2 foot pallet is 207.9 pounds per square foot, five times the 40 pounds per square foot a wood framed floor is designed to carry. A garage slab or a basement floor takes it without complaint, which is why barrels belong there and not on a deck.

Payload decides the drive home. A half ton pickup is rated near 1,000 pounds, so twenty cubic feet of water passes the rating before the driver climbs in, and a 5 gallon jug at 41.65 pounds means thirty jugs is 1,250 pounds spread across the bed. Two trips with the jugs upright beat one trip with them rolling.

Freeze is the other load. Water expands about 9 percent when it turns to ice, so a barrel left full over a hard freeze splits along the seam. Drain to 80 percent in fall, or move the stock indoors and refill in spring.

What twenty cubic feet costs at four rates

Per gallon, per cubic foot, per yard

A rate per gallon becomes a rate per cubic foot with one multiplication. At $0.10 a gallon, twenty cubic feet costs 149.6104 x 0.10 = $14.96, which is $0.75 per cubic foot and $20.20 per cubic yard at that same rate. Utilities quote 1,000 gallons, bulk yards quote the cubic yard, and bagged goods quote the bag, so a single price column is the only way to compare three quotes that arrive in three units.

Municipal water makes every other row look expensive. A utility charging $4.20 per 1,000 gallons sells twenty cubic feet for 149.6104 / 1,000 x 4.20 = $0.63. Bottled water at a dollar a gallon turns the same volume into $149.61, and bagged concrete at $6.85 for 80 pounds turns it into $232.90, which is 370 times the tap water price for a material that comes out of a hole.

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