Article — Cubic Feet to Pounds Converter
Cubic Feet to Pounds: How Material Density Sets the Weight
One cubic foot of water weighs 62.43 lb at 4°C. The same cubic foot of concrete weighs 150 lb, sand weighs 100 lb, gravel weighs 105 lb, mulch weighs 35 lb, and granite weighs 168 lb. To convert cubic feet to pounds, multiply the volume by the material density in lb/ft³. There is no single conversion factor because each material packs atoms differently.
The water baseline matters because every other density compares back to it. Anything denser than 62.43 lb/ft³ sinks; anything lighter floats. The numbers below cover the materials people search for most often: construction aggregates, landscaping bulk products, and shipping cargo.
The 62.43 lb water baseline
The weight of a cubic foot of water is a derived number, not a measurement. The metric system defines one liter of water at 4°C as exactly one kilogram. A cubic foot equals 28.3168 liters, and 28.3168 kg converts to 62.428 lb. That is where the 62.43 figure comes from. NIST publishes it to six decimal places (62.428000 lb at 4°C), but trade tables round to 62.4 or 62.43.
Most other materials in this article were measured against water as the reference. The ratio of a material's density to water's is called specific gravity. Concrete has SG 2.4, meaning a cubic foot weighs 2.4 times what a cubic foot of water weighs, or 150 lb. Granite has SG 2.69, giving 168 lb/ft³. Mulch has SG 0.56 — it is mostly air, which is why a pile of it does not feel heavy.
The 62.43 figure changes by less than 0.5 percent across the entire liquid-water temperature range. Cold water (4°C) is the densest at 62.428 lb/ft³. Hot water (80°C) drops to 62.18 lb/ft³. Even boiling water (100°C, before phase change) is still 59.83 lb/ft³. This means weight calculations using the 62.4 baseline are accurate for any water temperature encountered in landscaping, plumbing, or aquariums.
Concrete in cubic feet and pounds
Standard normal-weight concrete weighs 150 lb per cubic foot. The variation depends on the aggregate. Concrete made with limestone aggregate sits at 145 lb/ft³; concrete with denser granite or trap rock reaches 155 lb/ft³. Lightweight structural concrete (made with expanded shale or pumice) drops as low as 90-115 lb/ft³, and insulating perlite concrete falls to 25-50 lb/ft³.
The 150 lb number drives every concrete order. A residential slab measuring 20 × 20 × 0.5 ft equals 200 ft³, which weighs 30,000 lb or 15 short tons. That is about 7.4 cubic yards — one truck of ready-mix. A standard concrete truck can carry 8 to 10 yd³ (32,000-40,000 lb), and its axles, suspension, and engine are sized to handle that. Estimating concrete in pounds is what tells the dispatcher how many trucks to schedule.
- Normal concrete 150 lb/ft³ (145-155 range)
- Lightweight structural 90-115 lb/ft³ (expanded shale aggregate)
- Insulating concrete 25-50 lb/ft³ (perlite or vermiculite)
- High-density 200-300 lb/ft³ (barite or iron-shot, radiation shielding)
- Reinforced concrete 155 lb/ft³ (the rebar adds about 5 lb/ft³)
- Asphalt concrete 145 lb/ft³ (paving)
Cubic-foot calculations give the theoretical concrete volume for a finished slab, but every pour loses material. Over-pour, spillage, uneven sub-grade and form deflection typically add 5-10 percent to the actual concrete needed. Industry rule is to order one extra cubic yard for any pour bigger than 5 yd³ — that is 4,050 lb of concrete in reserve. Running out mid-pour is far more expensive than wasting some at the end.
Landscaping: soil, gravel, mulch
Bulk landscape materials behave differently than concrete because they are not bound together. Loose density varies with grain size and moisture. Topsoil averages 75-100 lb/ft³ when dry and freshly screened; once it settles in place and absorbs rain, it can reach 110 lb/ft³. Garden suppliers usually quote the dry density because it is the value tested by ASTM standards.
Gravel runs 95-110 lb/ft³ depending on size. Pea gravel (small rounded particles) packs tighter than crushed stone (angular fragments) because the rounded shape fills voids better. Mulch and wood chips weigh only 25-45 lb/ft³ because the wood structure holds large air gaps. A cubic yard of pine bark mulch weighs 800-1,000 lb, which is light enough to deliver in a pickup truck but heavy enough to need a wheelbarrow to spread.
Wet versus dry density adjustments
Bulk material density jumps when water fills the pore spaces between particles. Dry sand averages 100 lb/ft³; saturated sand reaches 125-130 lb/ft³ because every void gets filled with 62.43 lb/ft³ of water. Topsoil shows the same pattern: 75 lb/ft³ when bone dry, 110 lb/ft³ when soaked. The increase is not because the soil itself got denser — the water filled the gaps.
Practical effect: a yard of freshly-delivered topsoil might weigh 2,025 lb in summer (dry) but 2,970 lb after a rain (wet). The pickup truck that hauls one might be over its rated capacity hauling the other. Suppliers usually deliver in the morning when material is driest, both to make their trucks lighter and to give the customer fluffier material that spreads easier.
For mid-project density estimates without instruments, fill a 5-gallon bucket with material to the brim (0.668 ft³ usable), weigh it on a bathroom scale, and divide. A bucket weighing 50 lb means the material is 50 ÷ 0.668 = 75 lb/ft³ — useful for unknown soil or mixed aggregate from a job site stockpile.
From cubic feet to cubic yards
Bulk material in the US is sold by the cubic yard, not the cubic foot. The conversion is one of the cleanest in unit math: 1 cubic yard equals exactly 27 cubic feet, because 1 yard equals 3 feet and 3 cubed is 27. To go from cubic-foot weights to yard weights, multiply by 27. Concrete at 150 lb/ft³ becomes 4,050 lb/yd³. Sand at 100 lb/ft³ becomes 2,700 lb/yd³.
This matters when you compare quotes from different suppliers. One yard of topsoil weighs about 2,000-2,500 lb depending on dryness. A landscaping supplier quoting "10 yards delivered" is shipping 20,000-25,000 lb of material on a single dump truck. That is at or above many local highway weight limits for tandem-axle trucks, which is why heavier loads come in tri-axle trucks or split deliveries.
water (ft³) × 62.43 = lbconcrete (ft³) × 150 = lbsand dry (ft³) × 100 = lbgravel (ft³) × 105 = lbmulch (ft³) × 35 = lbgranite (ft³) × 168 = lbShipping, trucking, and load limits
Freight rates use weight, not volume, for dense cargo. A 40-foot ocean container holds 2,390 ft³, but its rated payload is 58,000-67,000 lb. Fill it with mulch (35 lb/ft³) and 2,390 ft³ would weigh 83,650 lb — over the 67,000 lb payload limit. So a mulch container hits the weight limit at about 1,914 ft³ of cargo (still nearly the full volume). Fill it with concrete blocks at 150 lb/ft³ and you hit the weight limit at 446 ft³ of cargo, leaving 80 percent of the container space empty.
This is why dense materials ship in less-than-container-load arrangements and lightweight materials fill containers entirely. A truckload of mulch is volume-limited at about 50-60 yd³. A truckload of concrete is weight-limited at about 8-10 yd³. The crossover material density is around 80 lb/ft³ — denser than that, weight is the limit; lighter, volume is the limit.