Slabs & rectangles
V = Length × Width × Thickness
Use for patios, driveways, garage floors, shed bases and sidewalks. Residential slabs are typically 4 in (10 cm); driveways 5–6 in (12–15 cm).
Slabs · Footings · Columns · Stairs
ConcreteCalculator
100% Free, Browser-Based Concrete Volume, Bags & Cost Estimator.
Concrete volume calculator
Slab / Rectangle
Patios, driveways, floors, pads & sidewalks.
Recommended 5–10%
%
Cost estimate (optional)
$
$
Formula used
Project list — combined pours
| Item | Dimensions | Volume (incl. waste) | |
|---|---|---|---|
| Total | |||
100% private — every calculation runs locally in your browser. Nothing is uploaded.
ConcreteCalculator key features
ConcreteCalculator is a free, 100% client-side concrete calculator that tells you how much concrete you need, in cubic yards, cubic feet or cubic meters, and how many pre-mixed bags to buy.
4 shape calculators
Slabs & rectangles, footings, circular columns / Sonotubes, and concrete stairs.
Imperial & metric units
Feet, inches, yards, meters, centimeters and millimeters — mix units per measurement.
Concrete bag calculator
Exact bag counts for 40 lb, 60 lb, 80 lb, 25 kg and 40 kg pre-mixed concrete.
Waste margin & cost
Custom waste % plus ready-mix vs. bagged cost comparison in your currency.
Copy, print & project list
Combine multiple pours, copy a material summary, or print / save a PDF estimate.
Private & secure
Runs entirely in your browser — no sign-up, no uploads, no backend server.
How to calculate how much concrete you need
Concrete is ordered by volume. Every calculation comes down to measuring the space you need to fill, converting all dimensions to the same unit, then adding a safety margin. ConcreteCalculator does the conversions for you, but here is the math behind each shape.
Footings
V = Length × Width × Depth × Qty
Continuous wall footings or square pad footings. Footings are usually at least twice as wide as the wall they support and must sit below the local frost line.
Circular columns & cylinders
V = π × (Diameter ÷ 2)² × Height × Qty
Sonotube piers, deck footings, fence and post holes. Measure the inside diameter of the form or the hole.
Stairs
V = Σ (Run × Width × Rise × i) + Platform
Calculated as solid steps poured on grade: each step is a block as tall as its height from the ground. The optional top platform is added at full stair height.
Unit conversions to remember
- • 1 cubic yard = 27 cubic feet = 0.7646 m³
- • 1 cubic meter = 35.31 cubic feet = 1.308 yd³
- • 4 inches = 0.333 ft · 6 inches = 0.5 ft
- • 10 cm = 0.10 m · 15 cm = 0.15 m
- • Normal concrete weighs ≈ 4,050 lb/yd³ (2,400 kg/m³)
- • A full ready-mix truck carries ≈ 10 yd³ (7.6 m³)
Worked example: 10 × 10 ft patio, 4 in thick
- Convert thickness to feet: 4 ÷ 12 = 0.333 ft.
- Volume: 10 × 10 × 0.333 = 33.33 ft³.
- Cubic yards: 33.33 ÷ 27 = 1.23 yd³.
- Add 10% waste: 1.23 × 1.10 = 1.36 yd³ (36.7 ft³).
- 80 lb bags: 36.7 ÷ 0.60 = 61.1 → 62 bags.
Ready-mix truck or bags?
Bagged concrete is practical for small jobs — post holes, steps, small pads — up to roughly 1 cubic yard (about 45 × 80 lb bags). Beyond that, mixing by hand becomes slow and risks cold joints, and a ready-mix delivery is usually cheaper per yard. Many suppliers charge a short-load fee for orders under 3–5 yd³, so compare both totals in the cost panel above.
Concrete bag yield chart
Typical yields for standard pre-mixed concrete. Yields vary slightly by brand — check the bag label.
| Bag size | Yield per bag | Bags per yd³ | Bags per m³ |
|---|---|---|---|
| 40 lb (18.1 kg) | 0.30 ft³ · 0.0085 m³ | 90 | 118 |
| 60 lb (27.2 kg) | 0.45 ft³ · 0.0127 m³ | 60 | 79 |
| 80 lb (36.3 kg) | 0.60 ft³ · 0.0170 m³ | 45 | 59 |
| 25 kg (55 lb) | 0.41 ft³ · 0.0117 m³ | 66 | 86 |
| 40 kg (88 lb) | 0.66 ft³ · 0.0187 m³ | 41 | 54 |
Frequently asked questions
How do I calculate how much concrete I need for a slab?
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Multiply length × width × thickness, with all three in the same unit. For a 10 ft × 10 ft slab that is 4 inches thick: 10 × 10 × (4 ÷ 12) = 33.33 cubic feet. Divide by 27 to get cubic yards: 33.33 ÷ 27 = 1.23 cubic yards. Then add 5–10% for waste, giving about 1.30–1.36 cubic yards.
How many 80lb bags of concrete make a cubic yard?
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One 80 lb bag of pre-mixed concrete yields about 0.60 cubic feet. A cubic yard is 27 cubic feet, so you need 27 ÷ 0.60 = 45 bags of 80 lb concrete per cubic yard. For 60 lb bags (0.45 cu ft) you need 60 bags, and for 40 lb bags (0.30 cu ft) you need 90 bags.
Why should I add a waste percentage to concrete orders?
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Real pours lose material to uneven subgrade, form bulging, spillage, over-excavation and concrete left in the truck, mixer or pump. Running short mid-pour can cause a cold joint that weakens the slab, so contractors typically add 5–10% extra, and up to 15% for irregular shapes or rough ground.
How many cubic yards of concrete do I need for a 10x10 slab?
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A 10 × 10 ft slab at 4 inches thick needs 1.23 cubic yards (33.3 cubic feet) before waste. At 6 inches thick it needs 1.85 cubic yards. Add 5–10% for waste.
How do I calculate concrete for a round column or Sonotube?
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Use the cylinder formula: volume = π × radius² × height. A 12-inch diameter column 8 ft tall is 3.1416 × 0.5² × 8 = 6.28 cubic feet, or 0.23 cubic yards — about 11 bags of 80 lb concrete.
How much does a 25 kg or 40 kg bag of concrete make?
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A 25 kg bag of pre-mixed concrete yields roughly 0.0117 cubic meters, so about 86 bags make one cubic meter. A 40 kg bag yields roughly 0.0187 cubic meters, so about 54 bags make one cubic meter. Exact yields vary slightly by brand.
Is this concrete calculator free and private?
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Yes. ConcreteCalculator is 100% free with no sign-up. All calculations run locally in your web browser using JavaScript; no measurements are sent to any server.