How Much Does a Cubic Foot of Concrete Weigh?
A cubic foot of normal-weight concrete weighs about 150 lb. Plain concrete without reinforcement is closer to 145 lb, and lightweight mixes run 90–115 lb.
That standard 150 lb/ft³ figure is where the familiar 4,050 lb per cubic yard comes from (150 × 27).
| Mix type | Per cubic foot | Metric | Where it's used |
|---|---|---|---|
| Lightweight (structural) | 90–115 lb | 1,440–1,840 kg/m³ | Upper floors, precast panels |
| Plain concrete | 145 lb | 2,320 kg/m³ | Unreinforced pads, fill |
| Standard reinforced | 150 lb | 2,400 kg/m³ | Slabs, footings, driveways |
| High-density | 160–180 lb | 2,560–2,880 kg/m³ | Counterweights, shielding |
Why 150 lb is the number to remember
150 lb per cubic foot (2,400 kg/m³) is the conventional design density for normal-weight reinforced concrete, and it is what estimating tools, span tables, and load calculations assume unless told otherwise.
The concrete itself is nearer 145 lb; the extra 5 lb accounts for steel reinforcement. For a bare, unreinforced pour, 145 is the more accurate figure — the difference is about 3%.
Slab weight per square foot
Multiply 150 lb by the thickness in feet to get weight per square foot of slab:
- 2 inches — 25 lb/sq ft
- 3 inches — 37.5 lb/sq ft
- 4 inches — 50 lb/sq ft
- 6 inches — 75 lb/sq ft
- 8 inches — 100 lb/sq ft
This is the calculation that decides whether a deck or balcony can carry a concrete topping. A 2-inch topping at 25 lb/sq ft is already a significant share of a typical residential live load allowance, so check with an engineer before adding one.
Useful conversions
- 1 cubic foot = 150 lb = 68 kg
- 1 cubic yard = 27 cubic feet = 4,050 lb
- 1 cubic metre = 2,400 kg = 5,300 lb
- An 80 lb bag makes 0.6 ft³, which weighs about 90 lb once mixed with water
Working out weight for a real pour
Get your volume in cubic feet, multiply by 150, and divide by 2,000 for tons. A 10 × 12 patio at 4 inches is 40 ft³ → 6,000 lb → 3 tons. The concrete volume calculator reports weight automatically and lets you set a custom density.
Estimating notes
- Aggregate type is the biggest driver of density — granite and basalt mixes weigh more than limestone or river gravel.
- Air-entrained concrete for freeze-thaw climates is slightly lighter, by roughly 3–6%.
- Weight figures assume properly consolidated concrete; honeycombed or under-vibrated pours weigh less and are weaker.