Estimate concrete volume in cubic yards or cubic meters for slabs, footings, round columns, and stairs.
Four shape modes with US/Metric unit toggle. Concrete bag calculator outputs counts for 60-lb (0.45 cubic feet) and 80-lb (0.60 cubic feet) bags, plus an automatic recommendation to switch to ready-mix truck delivery when volume exceeds 1 cubic yard. Includes a 0 to 20% waste factor slider.
Disclaimer: Always order 5 to 10% extra concrete to account for spillage, settling, and uneven subgrade. For structural slabs, footings, or walls, consult a licensed contractor and verify local PSI requirements (typically 3000 to 5000 PSI).
Loading calculator…
Calculator information
📋 How to use this calculator
- Select shape: Slab (rectangular flat surface), Footing (linear trench), Column (cylindrical pier), or Stairs (multi-step).
- Choose units: US (feet/inches/cubic yards) or Metric (meters/centimeters/cubic meters).
- For slab: enter length, width, thickness (typical 4 inch / 10 cm for patios, 6 inch / 15 cm for driveways).
- For column: enter diameter and height; for stairs: tread depth, riser height, width, number of steps.
- Apply waste factor 5-10% for simple slabs, 10-15% for footings/columns, 15-20% for irregular shapes.
- Tip: Above 1 cubic yard (~0.76 m3), order ready-mix delivery (cheaper per yard); below, use bagged concrete (60 lb yields 0.45 ft3, 80 lb yields 0.6 ft3).
🧮 Concrete Volume by Shape
Slab: V = L x W x T; Column: V = pi x r^2 x h; Stairs: V = W x sum(tread x riser, accumulating)
- L, W, T: length, width, thickness (consistent units)
- r: radius = diameter/2
- h: height of column
- Conversion: 1 cubic yard = 27 cubic feet = 0.7646 cubic meters
- Bag yield: 60 lb bag = 0.45 ft3 (0.0127 m3); 80 lb bag = 0.6 ft3 (0.017 m3)
- Waste factor: typically 5-20% added to net volume
Ready-mix trucks typically require a minimum 1 cubic yard order. Below the threshold (often <3 yd3) you'll pay a short-load fee. Concrete settles about 5% on placement.
💡 Worked example: Concrete Driveway Slab 20 ft x 12 ft x 6 inch
Given:- Length 20 ft, Width 12 ft, Thickness 6 inch (0.5 ft)
- Reinforced with wire mesh (standard residential driveway)
- Waste factor 10%
- Comparing bagged vs ready-mix
Steps:- Volume: 20 x 12 x 0.5 = 120 ft3
- Convert to cubic yards: 120 / 27 = 4.44 yd3
- Apply 10% waste: 4.44 x 1.10 = 4.89 yd3 (round to 5 yd3)
- Ready-mix cost estimate at $130/yd3 (US 2025 average): 5 x $130 = $650 plus delivery $80-150 = ~$750 total
- If bagged 80-lb: 120 ft3 / 0.6 ft3 per bag = 200 bags, plus 10% = 220 bags
- At $5.50/bag: 220 x $5.50 = $1,210 plus mixing labor/equipment
- Bagged is ~60% more expensive AND requires far more labor for 5 yd3 project
Result: 5 cubic yards ready-mix recommended at ~$750 vs ~$1,200 for bagged. Always order ready-mix for slabs over 1 yd3.
❓ Frequently asked questions
How many 80-lb bags of concrete in a cubic yard?
Each 80-lb bag of pre-mixed concrete yields approximately 0.6 cubic feet when set. One cubic yard = 27 cubic feet, so 27 / 0.6 = 45 bags per cubic yard. For 60-lb bags (0.45 ft3 yield), it takes 60 bags per cubic yard. Always add 5-10% waste. For projects exceeding 1 cubic yard, ready-mix delivery is more economical and consistent than mixing dozens of bags manually.
What thickness of concrete do I need?
Standard residential thicknesses: 4 inches (10 cm) for patios, walkways, and indoor floors; 5-6 inches (12-15 cm) for driveways supporting cars and light trucks; 6-8 inches (15-20 cm) for heavy vehicles, RVs, or shop floors. Footings: 8-12 inches (20-30 cm) typical for residential foundations. Always check local building codes and frost depth (footings must be below frost line, often 12-48 inches in cold climates).
How much waste should I add to my concrete order?
Standard waste factors: 5-10% for simple rectangular slabs (spillage, slight over-pour), 10-15% for footings and complex shapes (forms not perfectly tight), 15-20% for stairs, curved walls, or projects with significant cuts. Ready-mix trucks must be fully discharged within ~90 minutes of mixing, so under-ordering is worse than over-ordering. Excess wet concrete is wasted (you cannot return it).
What is the difference between concrete and cement?
Cement (typically Portland cement) is the binder powder. Concrete is the finished material: cement + aggregate (sand and gravel) + water. Mortar is cement + sand + water (no gravel), used for bricklaying. Standard concrete mix is roughly 1 part cement : 2 parts sand : 3 parts gravel : 0.5 parts water by volume. Pre-mixed bags contain all dry components - you just add water.
How long does concrete take to cure?
Concrete reaches initial set in 4-8 hours, walkable in 24-48 hours, and 70% of full strength in 7 days. Full design strength (28-day compressive strength, typically 3,000-4,000 psi for residential) is achieved at 28 days. Heavy vehicle traffic should wait 7+ days. Curing temperature matters: below 50 deg F (10 deg C) curing slows significantly; above 90 deg F (32 deg C) concrete dries too fast and may crack. Keep moist for first 7 days for optimal strength.
📚 Sources & references
Last updated: May 11, 2026