Concrete volume.
Concrete volume: Calculate concrete volume for slabs, footings, and post holes in cubic yards, cubic meters, and number of 60/80 lb bags.
Concrete volume for slabs, footings, and post holes with a waste-factor multiplier. Output in cubic yards, cubic meters, and bag count (60 lb and 80 lb).
How this works
Concrete volume is straightforward geometry:
Slab / footing: V = L × W × T Post hole / column: V = π × (D/2)² × H Total order = V × (1 + waste fraction)
Bag-count math
Pre-mixed concrete bags yield approximately:
- 60 lb bag: 0.45 ft³ (≈ 0.0127 m³) of finished concrete
- 80 lb bag: 0.60 ft³ (≈ 0.0170 m³)
- 40 lb bag: 0.30 ft³ (≈ 0.0085 m³)
Yield varies by manufacturer — Quikrete, Sakrete, and others publish slightly different numbers. The values above are typical for general-purpose concrete mix.
When to order ready-mix vs bags
The rough breakeven is about 1 cubic yard (≈ 27 ft³, ≈ 0.76 m³). Below that, bags are cheaper and you don't have ready-mix truck minimums to worry about. Above 1 cu yd, ready-mix becomes more economical and far faster (one truck delivers 8-10 cu yd vs ~60 bags per yard).
Common pitfalls
- Always order extra. Concrete can't be added partway through — once you've started pouring, you're committed. 10% waste is standard for rectangular pours; 15-20% for irregular shapes or anything below grade where the soil may absorb some.
- Footing dimensions vary by frost line and soil bearing capacity. The minimum thickness shown here is a typical residential value — check your local building code for required depth (frost line) and footing dimensions (soil-bearing).
- Bag concrete vs ready-mix have different strengths. Bag concrete is typically 4000 psi but can vary. Ready-mix is specified to your spec (3000, 4000, 4500 psi etc.) and tested.
- Don't forget reinforcement. Most concrete in modern construction includes rebar, wire mesh, or fiber reinforcement. The cost is separate from the concrete itself but should be planned together.
- Settle factor for post holes. Concrete compacts about 2-3% as it cures. For tall, narrow pours (post holes, columns), overfill slightly to compensate.
Concrete weight, density, and moisture
Volume tells you how much to order; density tells you how much it weighs. Normal-weight concrete has a volumetric mass density of about 150 lb/ft³ — roughly 4,050 lb (about 2 tons) per cubic yard, or 2,400 kg/m³. That weight drives formwork bracing, wheelbarrow counts, transport, and the floor loading a slab imposes on the structure below.
| Concrete type | Density (lb/ft³) | Per cubic yard |
|---|---|---|
| Normal-weight (plain) | 145–150 | ~3,900–4,050 lb |
| Reinforced (with rebar) | 150–156 | ~4,050–4,200 lb |
| Structural lightweight | 90–115 | ~2,430–3,100 lb |
| Heavyweight (barite/magnetite) | 180–300 | ~4,860–8,100 lb |
Aggregate moisture offset
Mix designs specify batch water against the saturated-surface-dry (SSD) condition of the aggregate — sand and gravel that are neither soaking up water nor giving it off. Real stockpiles are rarely at SSD, so the batch water has to be corrected or the water-to-cement ratio (and therefore the strength) drifts:
- Wet aggregate (free surface moisture). The stone carries extra water on its surface. Subtract that free water from the mix water, or the batch ends up too wet and weak.
- Dry or absorptive aggregate. The stone will soak up water from the mix. Add water equal to the absorption deficit so the paste is not starved.
- Rule of thumb. Adjusted water = design water − free surface moisture + absorption shortfall. A 1% moisture swing on the sand in a yard of concrete is several pounds of water — enough to matter.
Cylinder volume geometry
Round pours — sonotube piers, deck footings, columns, filled pipe — are not covered by slab length × width math. Use the cylinder formula: volume = π × r² × height, where r is the radius (half the diameter). Keep every dimension in feet, then divide by 27 to get cubic yards. Example: a 12-inch (1 ft) diameter tube 4 ft deep holds π × 0.5² × 4 = 3.14 ft³ = 0.116 cubic yards. For several identical piers, multiply by the count before ordering.
Common questions
How many cubic feet are in a yard of concrete?
A cubic yard of concrete is exactly 27 cubic feet (3 ft × 3 ft × 3 ft). Work out your volume in cubic feet (length × width × depth, all in feet) and divide by 27 to get yards.
How much concrete do I need for a 10×10 slab?
A 10×10 ft slab poured 4 inches thick needs about 1.24 cubic yards (roughly 33.3 cubic feet). Add about 10% for uneven subgrade, spillage and waste, so order closer to 1.35 cubic yards.
How many 80 lb bags of concrete make a yard?
About 45 bags. An 80 lb bag of pre-mixed concrete yields roughly 0.6 cubic feet, and a cubic yard is 27 cubic feet, so 27 ÷ 0.6 ≈ 45 bags.
How deep should a concrete driveway slab be?
Four inches is the minimum for a residential car driveway over a compacted aggregate subbase. Increase to 5–6 inches where heavier vehicles or light trucks park.
How long does concrete take to cure fully?
Concrete is usually firm enough to bear foot traffic in 24 to 48 hours, but it keeps gaining strength for weeks and reaches its full design strength at about 28 days through ongoing hydration.
How do you calculate concrete yardage for a round deck post?
Use the cylinder volume formula: volume = π × radius² × depth. Keep every dimension in feet, then divide the result by 27 to convert cubic feet to cubic yards.
What is the standard mix ratio for 4000 PSI concrete?
A typical 4000 PSI mix is about 1 part cement, 1.5 parts sand and 3 parts gravel by volume, with minimal water (a low water-to-cement ratio). Exact proportions vary by aggregate and admixtures.
How many concrete blocks are needed per square foot of wall?
A standard 8×8×16-inch block has a 16×8-inch face covering about 0.89 square feet, so it takes roughly 1.125 blocks per square foot of wall (before deducting for mortar joints and openings).
How much does a cubic yard of wet concrete weigh?
Standard gravel-aggregate concrete weighs roughly 4,000 pounds (about 2 tons) per cubic yard when freshly mixed. Lightweight mixes weigh less.
What size footing do I need for a two-story deck post?
A typical footing for a two-story load runs about 20 to 24 inches in diameter, with the base placed below the local frost line to prevent heaving. Size to your actual tributary load and soil bearing capacity per code.
How much sand and gravel do I need for 1 yard of concrete?
Roughly 1,400 lb of sand, 2,100 lb of gravel and about 560 lb of cement make one cubic yard of mixed concrete — the exact split depends on the target strength and mix design.
How thick should a concrete patio slab be poured?
A standard backyard pedestrian patio needs a minimum thickness of 4 inches, with perimeter forms and a slight slope for drainage away from structures.
How many 60 lb bags of concrete equal one yard?
About 60 bags. A 60 lb bag yields roughly 0.45 cubic feet, and a cubic yard is 27 cubic feet, so 27 ÷ 0.45 = 60 bags.
How do you calculate gravel tonnage for a driveway base?
Multiply the area in square feet by the depth in feet to get cubic feet, then convert to tons using the gravel's density (about 100 lb per cubic foot) and add roughly 30% for compaction. In short: square feet × depth (ft) × ~0.05 × 1.35 ≈ tons.
What is the maximum distance between concrete control joints?
Space control joints no farther apart (in feet) than about 2.5 to 3 times the slab thickness in inches — for a 4-inch slab that is roughly every 10 to 12 feet.
How many cubic meters are in a cubic yard?
One cubic yard equals about 0.7646 cubic meters. Multiply cubic yards by 0.7646 to get cubic meters, or divide cubic meters by 0.7646 to go the other way.
How many bags of mortar do I need for 100 blocks?
Laying 100 standard 8×8×16 blocks typically takes about 3 to 3.5 bags of Type S mortar mix, depending on joint size and waste.
How deep must a residential foundation footer be placed?
Code generally requires the bottom of a footing to rest at least 12 inches below undisturbed ground and below the local frost depth — whichever is deeper.
How do you convert square feet to cubic yards for gravel?
Multiply the area in square feet by the layer thickness in feet to get cubic feet, then divide that volume by 27 to convert to cubic yards.
What is the structural difference between Type N and Type S mortar?
Type N is a medium-strength mortar (about 750 PSI minimum) for general above-grade walls. Type S is a high-strength mortar (about 1,800 PSI minimum) used for below-grade and load-bearing applications.
What is the minimum slope required for a concrete slab drainage floor?
Exterior slabs, garage floors and showers need a minimum slope of about 1/4 inch per foot (a 2% grade) to drain properly.
How deep do you bury a 4x4 fence post?
Set a fence post to about one-third to one-half of its above-ground height. A 6-foot fence generally calls for posts buried 2 to 3 feet deep, below the frost line.
Sources
- Standard yield values: Quikrete and Sakrete bag specifications.
- Concrete mix design: ACI 211.1 — Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass Concrete.
- Residential foundations: ACI 332 / IRC Chapter 4 for foundations.
Disclaimer. This is a volume calculator for ordering material. Footing dimensions, depth, reinforcement, and structural requirements are governed by local code and should be designed by a qualified professional for any load-bearing application.