Concrete Volume Calculator
Concrete Volume
1.30 cubic yards
35.0 cu ft • includes 5% waste factor
Cubic Feet
35.0
Gallons
262
Weight
5,250 lbs
80 lb Bags
59
Quick Reference: 80 lb bag = 0.60 cu ft • 60 lb = 0.45 cu ft • 40 lb = 0.30 cu ft. Ready-mix delivery starts at ~$125/cu yd.
Disclaimer: Estimates are for budgeting purposes only. Actual costs vary by location, contractor, material availability, and project complexity. Always get professional quotes for exact pricing.
Concrete Volume Formulas & Unit Conversions
Volume Formulas by Shape
| Shape | Formula | Example |
|---|---|---|
| Slab / Rectangle | L × W × T | 10 × 12 ft × 4″ = 1.48 cu yd |
| Cylinder / Sono Tube | π × r² × h | 12″ dia × 48″ deep = 3.14 cu ft |
| Stairs | (Steps × Rise × Run × W) ÷ 2 + base | 4 steps, 7″ rise, 3 ft wide ≈ 0.4 cu yd |
| Footing (rectangular) | L × W × D (outer − inner void) | 24″ × 12″ × 50 ft = 2.78 cu yd |
Common Concrete Unit Conversions
| From | To | Multiply By |
|---|---|---|
| Cubic Yards | Cubic Feet | 27 |
| Cubic Yards | Gallons | 201.97 |
| Cubic Yards | Weight (lbs) | 4,050 |
| Cubic Feet | Gallons | 7.48 |
| Cubic Feet | Weight (lbs) | 150 |
* Weight based on standard-weight concrete at 150 lbs/cu ft. Lightweight mixes weigh 100–120 lbs/cu ft.
How We Calculate
Our concrete volume calculator computes volumes for rectangular slabs, cylinders (sono tubes / post holes), stairs, and footings using standard geometry formulas. Results are displayed in cubic yards, cubic feet, gallons, and weight (lbs).
How the math works: Slab: L × W × T (in feet). Cylinder: π × r² × h. Stairs: (steps × rise × run × width) ÷ 2 + base slab. Footing: (outer volume) − (inner void). All results include a 5% waste factor by default, adjustable up to 15%.
Shape Formulas
Rectangle / Slab: Volume = length × width × depth. This is the most common shape for patios, sidewalks, driveways, and garage floors. Convert all measurements to feet before multiplying, then divide by 27 to get cubic yards.
Cylinder: Volume = π × radius² × height. Used for sono tubes, post holes, round columns, and piers. Measure the diameter and divide by 2 to get the radius. Our calculator accepts diameter directly for convenience.
Stairs: Volume = (number of steps × rise × run × width ÷ 2) + (base length × width × base thickness). The triangular cross-section of each step accounts for half the rectangular envelope.
Unit Conversions
1 cubic yard = 27 cubic feet = 201.97 gallons = ~4,050 lbs. 1 cubic foot = 7.48 gallons = ~150 lbs. These conversions assume standard-weight concrete at 150 lbs/cu ft (2,400 kg/m³). Lightweight concrete mixes weigh 15–30% less.
Waste Factor
We apply a default 5% waste factor to account for spillage, over-excavation, uneven sub-grade, and form imperfections. Increase to 10% for irregular shapes or loose soil conditions. The waste factor is applied after the base volume calculation: total = base volume × (1 + waste%).
Data Sources
Geometry formulas follow standard mathematical principles. Concrete weight (150 lbs/cu ft) is per ACI 318. Unit conversions use exact NIST values. Waste factor recommendations are based on contractor best practices and ACI guidelines.
Last updated: 2026-02-08
Frequently Asked Questions
How do I calculate concrete volume for a rectangular slab? +
Multiply length × width × thickness, all in the same unit. For feet and inches: convert thickness to feet first (divide inches by 12). A 10 × 12 ft slab at 4″ thick = 10 × 12 × 0.333 = 40 cu ft = 1.48 cu yd. Always add 5–10% for waste, uneven sub-grade, and form over-pour.
How much does a cubic yard of concrete weigh? +
A cubic yard of standard-weight concrete weighs approximately 4,050 lbs (about 2 tons). Lightweight concrete weighs 2,800–3,500 lbs per cubic yard depending on the aggregate. One cubic foot of concrete weighs about 150 lbs. These weights matter when calculating truck loads and structural support requirements.
How do I convert between cubic yards, cubic feet, and gallons? +
1 cubic yard = 27 cubic feet = 201.97 gallons. 1 cubic foot = 7.48 gallons = 0.037 cubic yards. To convert cubic feet to cubic yards, divide by 27. To convert cubic yards to gallons, multiply by 202. Our calculator displays all units simultaneously so you never need to convert manually.
What waste factor should I add to my concrete volume? +
Add 5–10% for most projects. Use 5% for flat slabs on well-prepared, level sub-grade. Use 10% for irregular shapes, slopes, footings with loose soil, or first-time DIY pours. For sono tubes and post holes, add 10% because concrete can seep into surrounding soil. Ready-mix trucks typically carry slightly more than ordered as a buffer.
How do I calculate concrete volume for stairs? +
Stair concrete volume = number of steps × step height × step depth × stair width ÷ 2 (for the triangular cross-section), plus the volume of the underlying slab/platform. A typical set of 4 steps at 7″ rise × 11″ run × 3 ft wide on a 4″ base slab needs roughly 0.35–0.50 cu yd. Our calculator handles the geometry automatically.
How do I calculate concrete for sono tubes and cylinders? +
Use the cylinder formula: volume = π × radius² × height. For a 12″ diameter sono tube at 48″ deep: radius = 0.5 ft, volume = 3.14 × 0.25 × 4 = 3.14 cu ft. Common sono tube volumes: 8″ dia × 4 ft = 1.40 cu ft, 10″ dia × 4 ft = 2.18 cu ft, 12″ dia × 4 ft = 3.14 cu ft. Multiply by the number of tubes and add 10% waste.
When should I use ready-mix concrete vs. bags? +
Use bagged concrete for projects under 0.5 cubic yards (about 45 bags of 80 lb mix). Use ready-mix delivery for anything over 1 cubic yard — it saves labor and ensures consistent quality. The gap between 0.5–1.0 cu yd depends on your budget and timeline. Ready-mix costs $125–$175/cu yd delivered; bags cost $225–$360/cu yd but require no minimum order.
How long does concrete take to cure? +
Concrete reaches initial set in 24–48 hours, working strength (50%) in 3–7 days, and full design strength (4,000 PSI) in 28 days. Keep concrete moist during the first 7 days — cover with plastic sheeting or mist with water daily. Temperature below 50°F slows curing significantly; above 90°F requires extra moisture. Never pour on frozen ground.
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