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Canada

Concrete Slab Calculator

Enter the size of your slab in feet and the thickness in inches. You get cubic yards and cubic metres, the 30 kg bags to buy and the ready-mix order, with rebar or mesh if you want it.

What are you pouring?
Patio, driveway, shed base, path
Length Width Thickness

Tip: you can type feet and inches, like 10' 6", or metric with its unit, like 3.2 m.

Reinforcement for slabs (optional)
Gravel base under slabs (optional)

Gravel weight changes from quarry to quarry: ask your supplier for the compacted weight and we turn the volume into tonnes.

Use your own prices (optional)

You need

– cu yd

–

Poured, it weighs about – kg.

Premixed bags

Bag Bags To carry Est. cost

Ready-mix truck

–

How we price

Link to this calculation Download estimate (PDF)

Your materials at a glance

How to calculate concrete

  1. Measure length and width. In feet, inside the forms. Split an L-shaped slab into two rectangles.
  2. Pick the thickness. In inches: 4 in for patios and walkways, 4–6 in for garage pads and driveways.
  3. Multiply. Length × width × (thickness ÷ 12) gives cubic feet.
  4. Add 5–10% extra. Ground is never perfectly flat and forms flex.
  5. Convert. ÷ 27 for cubic yards, ÷ 35.31 for cubic metres, × 2 for 30 kg bags (½ cu ft each).

Worked example: a 12 × 20 ft garage pad, 5 inches thick

  1. Volume: 12 × 20 × (5 ÷ 12) = 100 cu ft. Plus 5%: 105.0 cu ft.
  2. 3.89 cubic yards, or 2.97 m³.
  3. Ready-mix: order 3.00 m³. In 30 kg bags it would be 213.

Concrete for common slab sizes

Slab Thickness Cubic yards m³ 30 kg bags
8 × 10 ft 4 in 1.04 0.79 57
8 × 10 ft 6 in 1.56 1.19 85
10 × 10 ft 4 in 1.30 0.99 71
10 × 10 ft 6 in 1.94 1.49 107
10 × 12 ft 4 in 1.56 1.19 85
10 × 12 ft 6 in 2.33 1.78 128
12 × 12 ft 4 in 1.87 1.43 102
12 × 12 ft 6 in 2.80 2.14 153
12 × 20 ft 4 in 3.11 2.38 170
12 × 20 ft 6 in 4.67 3.57 255
20 × 20 ft 4 in 5.19 3.96 284
20 × 20 ft 6 in 7.78 5.95 425
24 × 24 ft 4 in 7.47 5.71 408
24 × 24 ft 6 in 11.20 8.56 612

Includes 5% extra for waste. 30 kg bags at 0.014 m³ each (Sakrete data sheet).

Concrete formulas by shape

All measurements in feet; divide inches by 12 first. Results are in cubic feet.

Slab
length × width × thickness
Round slab
π × (diameter ÷ 2)² × thickness
Monolithic slab
length × width × thickness + perimeter band × (edge depth − thickness), where perimeter band = length × width − (length − 2 × edge width) × (width − 2 × edge width)

Cubic yards = cubic feet ÷ 27. Cubic metres = cubic feet ÷ 35.31.

Frequently asked questions

How thick should a concrete slab be?

Patios and walkways are usually 4 inches, garage pads and driveways 4 to 6 inches. Your building permit and the code for your province have the final word.

How many 30 kg bags for a 10x10 slab?

At 4 inches with 5% extra: 71 bags, about 1.30 cubic yards or 0.99 m³.

What rebar is used in slabs in Canada?

Metric bars: 10M (11.3 mm) for most slabs on grade, 15M for heavier work. Open "Reinforcement for slabs" in the calculator to count 10 or 20 ft bars for your spacing.

How many square feet does a yard of concrete cover?

81 sq ft at 4 inches thick, 65 sq ft at 5 inches and 54 sq ft at 6 inches.

About the prices

Costs are estimated ranges with source and date, never a quote. Enter your local prices under "Use your own prices", or read how we estimate prices.