Free estimating tool
Concrete Calculator
Estimate concrete for slabs, round footings, tubes, curbs, walls and stairs — with volume, weight, bags and cost.
Rectangular slab · incl. 10% waste
You need approximately 1.358 cubic yards
36.667 ft³ · 1.038 m³ · 1,038.28 litres
Volume
| Unit | Exact | +10% waste |
|---|---|---|
| Cubic yards | 1.235 | 1.358 |
| Cubic feet | 33.333 | 36.667 |
| Cubic metres | 0.944 | 1.038 |
| Litres | 943.895 | 1,038.284 |
Placed weight · incl. waste
5,500 lb / 2,494.76 kg
Density: 150 lb/ft³ · weight = volume × density
Selected premix bags · incl. waste
62 × 80 lb bags
Yield: 0.6 ft³ / bag · total volume ÷ yield, rounded up.
Above about 1 yd³, ready-mix is often more practical than mixing bags.
Estimate inputs & formula
Length: 10 ft · Width: 10 ft · Thickness (H): 4 in · Quantity (Q): 1
V = L × W × H × Q
Estimate only, not engineering advice. Actual needs vary with subgrade, forms and spillage. Confirm final quantities and product yields with your supplier or contractor before ordering.
How to calculate concrete
Concrete is measured by volume. For any rectangular pour, multiply the three dimensions in the same unit, then convert to the unit your supplier sells in.
Cubic yards = (length ft × width ft × thickness ft) ÷ 27
Convert inches to feet by dividing by 12, so a 4 inch slab is 0.333 ft. A 10 × 10 ft slab at 4 inches is 33.3 cubic feet, or 1.23 cubic yards. For a full walkthrough, read how much concrete do I need.
What are you calculating?
Slab or patio
Length × width × thickness
Open calculator →
Driveway
Volume + optional cost
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Footings
Strip and pad footings
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Round footings & holes
Diameter × depth × count
Open calculator →
Walls
Poured and stem walls
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Columns
Round piers and tubes
Open calculator →
Steps
Exact stepped solid
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Curb & gutter
Non-overlapping prisms
Open calculator →
Circular & tube
Outer minus inner cylinder
Open calculator →
Bags
Editable product yields
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Cost
Itemized from your quotes
Open calculator →
Post holes
Fence and deck posts
Open calculator →
Conversion reference
| 1 cubic yard | 27 cubic feet | 0.7646 m³ |
|---|---|---|
| 1 cubic foot | 0.037 cubic yards | 0.0283 m³ |
| 1 cubic metre | 1.308 cubic yards | 35.31 cubic feet |
| 1 cu yd at 4 in thick | covers ≈ 81 sq ft | ≈ 7.5 m² |
| 1 cu yd at 6 in thick | covers ≈ 54 sq ft | ≈ 5.0 m² |
| 80 lb bag | ≈ 0.60 cu ft | 45 bags per cu yd |
| 60 lb bag | ≈ 0.45 cu ft | 60 bags per cu yd |
| 40 lb bag | ≈ 0.30 cu ft | 90 bags per cu yd |
Bag yields are typical; check the label on the product you buy.
Why add a waste allowance?
Real pours rarely match the drawing. Subgrade dips, forms bow, some concrete stays in the mixer or wheelbarrow, and a bit always spills.
- 5% — accurate forms on a compacted, level base.
- 10% — a sensible default for most DIY slabs.
- 15%+ — trenches, uneven ground or complex shapes.
Running short mid-pour can leave a weak cold joint, so a small surplus is usually the cheaper mistake.
Frequently asked questions
How do I calculate how much concrete I need?
Multiply length × width × thickness in feet to get cubic feet, then divide by 27 for cubic yards. Add 5–10% for waste and round up.
How many cubic feet are in a cubic yard?
There are 27 cubic feet in one cubic yard (3 ft × 3 ft × 3 ft), which is about 0.765 cubic metres.
How many 80 lb bags of concrete are in a yard?
At a typical yield of 0.60 cubic feet per bag, about 45 bags of 80 lb premix make one cubic yard.
How much waste should I add?
Around 5–10% is common for formed slabs on a level base. Use more for trenches, uneven ground or first-time pours.
Is this calculator engineering advice?
No. It estimates volume from the dimensions you enter. Structural requirements such as thickness, reinforcement and footing size should come from your plans, local code or a qualified professional.