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Concrete Calculator: Cubic Yards, Bags, Slabs & Footings

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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.

Calculator

Switch units; we’ll convert outputs to both yd³ and m³.
Covers spillage, uneven subgrade, and pump line loss.
Use this when adding multiple sections to the project total.
Use decimals for inches/centimetres (e.g., 4.5 in → 0.375 ft).
Typical patios/sheds: 4–6 in (100–150 mm). Heavier loads need engineering.
Rectangular slab dimensions length width thickness
Slab results will appear here.
Round slab dimensions diameter thickness
Round slab results will appear here.
Footing dimensions length width depth
Footing/trench results will appear here.
Cylinder dimensions diameter depth
Cylinder results will appear here.
Common sonotubes: 8, 10, 12 in (200–300 mm).
Post hole dimensions diameter depth
Post hole results will appear here.
Wall dimensions length height thickness
Wall results will appear here.
Steps dimensions run rise width
Uses a solid stair-flight estimate: width x run x rise x steps x (steps + 1) / 2.
Step results will appear here.
Curb and gutter dimensions length curb height curb width gutter width
Curb and gutter results will appear here.

Project Total & Bags

Base Volume
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With Waste
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Ordering Guidance
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Cubic Feet
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Estimated Weight
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Waste Setting
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Common bag counts:
Bag sizeYieldBags
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Bag yields are typical; always check your product's stated yield.
Cost Estimate
Enter prices to estimate cost.

Project Total

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.

How this Concrete Calculator Works

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.

Concrete Estimating Guides

Thickness Guide

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.

Bag Yield Table

40 lbabout 0.30 ft³
50 lbabout 0.375 ft³
60 lbabout 0.45 ft³
80 lbabout 0.60 ft³
90 lbabout 0.675 ft³
20-30 kgabout 0.009-0.013 m³

Waste Guide

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.

Ready-Mix vs Bagged

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.

Common Project Examples

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.

Worked Examples

10 ft x 10 ft x 4 in slab

10 x 10 x (4 / 12) = 33.33 ft³ = 1.235 yd³

With 10% waste: 1.358 yd³. Bag estimate: 82 bags of 60 lb or 62 bags of 80 lb.

20 ft x 12 ft patio, 4 in thick

20 x 12 x (4 / 12) = 80.00 ft³ = 2.963 yd³

With 10% waste: 3.259 yd³. Bag estimate: 196 bags of 60 lb or 147 bags of 80 lb.

Six 12 in x 36 in post holes

pi x 0.5² x 3 x 6 = 14.14 ft³ = 0.524 yd³

With 10% waste: 0.576 yd³. Bag estimate: 35 bags of 60 lb or 26 bags of 80 lb.

Strip footing, 40 ft x 16 in x 8 in

40 x (16 / 12) x (8 / 12) = 35.56 ft³ = 1.317 yd³

With 10% waste: 1.449 yd³. Bag estimate: 87 bags of 60 lb or 66 bags of 80 lb.

Round tube, 18 in diameter x 4 ft

pi x 0.75² x 4 = 7.07 ft³ = 0.262 yd³

With 10% waste: 0.288 yd³. Bag estimate: 18 bags of 60 lb or 13 bags of 80 lb.

Concrete Calculator FAQ

How many 80 lb bags of concrete are in a cubic yard?

An 80 lb bag commonly yields about 0.60 ft³. Since 1 yd³ is 27 ft³, 27 / 0.60 = 45 bags before waste.

How much extra concrete should I order?

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.

Should I use bagged concrete or ready-mix?

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.

How much does a cubic yard of concrete weigh?

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.

How do I handle irregular concrete shapes?

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.

What thickness should I use for a sloped slab?

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.

How long does concrete take to cure?

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.

Methodology & Trust Notes

  • Last updated: June 9, 2026.
  • Formula basis: rectangular prisms use length x width x depth, round sections use pi x radius squared x depth, and all totals are converted through cubic feet.
  • Bag yields: common estimating yields are based on typical premix manufacturer labels for 40 lb, 50 lb, 60 lb, 80 lb and 90 lb bags, plus common 20 kg, 25 kg and 30 kg metric bag yields. Product yields vary, so check the label before ordering.
  • Safety note: structural footings, walls, slabs supporting loads, frost-depth requirements and permitted work should follow local code or a qualified engineer.

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