Calculate cubic yards, cubic metres, cubic feet, bag counts, concrete weight, costs and waste-adjusted ordering quantities for slabs, footings, post holes, round slabs, walls, steps, curbs, gutters and ready-mix orders.
| Bag size | Yield | Bags |
|---|---|---|
| — | ||
For irregular slabs, calculate rectangles, circles or strips separately, then add each section here. Use average thickness for sloped pours.
| Section | Base yd³ | Base m³ | Actions |
|---|---|---|---|
| No sections yet. Calculate a mode to add to the project total. | |||
Volume = area x thickness. Rectangular slabs, walls and strip footings use length x width x depth or thickness. Round slabs, tubes and post holes use pi x radius squared x depth. Steps use a solid stair-flight estimate. Curb and gutter mode adds the curb cross-section to the gutter cross-section, then multiplies by length.
Conversions: 1 cubic yard = 27 cubic feet. 1 cubic metre = 35.3147 cubic feet. The calculator keeps an internal cubic-foot total and displays cubic feet, cubic yards and cubic metres so you can order ready-mix in the unit your supplier uses.
Irregular shapes: break complex slabs into rectangles, round sections or strips, calculate each section, and use the project total. For sloped pours, use average thickness: (thin edge + thick edge) / 2.
Walkways and shed pads are often 3-4 in. Patios and light-use slabs are commonly 4 in. Driveways are often 4-5 in or more with reinforcement and proper base. Footings, walls and structural slabs should follow local code or an engineer.
| 40 lb | about 0.30 ft³ |
|---|---|
| 50 lb | about 0.375 ft³ |
| 60 lb | about 0.45 ft³ |
| 80 lb | about 0.60 ft³ |
| 90 lb | about 0.675 ft³ |
| 20-30 kg | about 0.009-0.013 m³ |
Use 5% for well-formed simple pours, 10% for typical DIY ordering, and 10-15% for rough subgrades, many small sections, hand mixing, pump line loss or forms that may bulge.
Bagged concrete is convenient for posts, small pads and repairs. Ready-mix is usually more practical for patios, driveways and larger slabs because placement is faster and the mix is more consistent.
Small post batches are often bagged. A 10 ft x 10 ft x 4 in pad is about 1.24 yd³ with 10% waste. A 20 ft x 12 ft x 4 in patio is about 3.26 yd³ with 10% waste, which usually points to ready-mix.
With 10% waste: 1.358 yd³. Bag estimate: 82 bags of 60 lb or 62 bags of 80 lb.
With 10% waste: 3.259 yd³. Bag estimate: 196 bags of 60 lb or 147 bags of 80 lb.
With 10% waste: 0.576 yd³. Bag estimate: 35 bags of 60 lb or 26 bags of 80 lb.
With 10% waste: 1.449 yd³. Bag estimate: 87 bags of 60 lb or 66 bags of 80 lb.
With 10% waste: 0.288 yd³. Bag estimate: 18 bags of 60 lb or 13 bags of 80 lb.
An 80 lb bag commonly yields about 0.60 ft³. Since 1 yd³ is 27 ft³, 27 / 0.60 = 45 bags before waste.
For many small and medium projects, 5-10% extra is common. Use more for uneven base, complex forms, pump line loss or pours where being short would stop the job.
Bagged concrete works well for post holes, small pads and repairs. Ready-mix is usually better for larger slabs, patios, driveways and pours that need consistent finishing time.
Normal-weight concrete is commonly estimated around 4,000 lb per cubic yard, or roughly 2,400 kg per cubic metre. The exact weight depends on the mix and aggregate.
Break the layout into rectangles, circles and strips. Calculate each section with its own dimensions, add it to the project total, and order from the waste-adjusted total.
Use average thickness for estimating: add the thin-edge thickness and thick-edge thickness, then divide by two. Structural or drainage-critical slabs should be checked against local requirements.
Set and cure timing depends on mix, temperature and moisture. Many slabs can take light foot traffic after about 24-48 hours, but strength develops over weeks. Follow the supplier's guidance for your mix.
