Measure Twice › Concrete
Concrete Patio Calculator
Replacing grass with concrete? Enter the slab size to get every layer, from how deep to dig to how much ready-mix to order.
Worked example
- Slab length 20 ft
- Slab width 20 ft
- Concrete thickness 4 in
- Gravel base (compacted) 6 in
- Finished slab above existing grade 1 in
- Reinforcement 10M rebar, 24 in (60 cm) grid
- Geotextile fabric under the base Yes (recommended on clay or soft soil)
- Concrete waste allowance 10%
Result:
- Ready-mix concrete to order
- 4.25 m³
- 1. Dig out (sod + soil) to depth
- 9 in
- 1. Soil to remove (loose, for bins/trucks)
- 13.89 yd³
- 1. Approx. weight of soil removed
- 13.6 tonnes
- 2. Geotextile fabric (+10% overlap)
- 440 ft²
- 3. Gravel base, compacted volume
- 7.41 yd³
- 3. Gravel base to order
- 11.3 tonnes
- 4. 10M rebar (20 ft bars, incl. laps)
- 22 bars
- 5. Concrete incl. waste
- 5.43 yd³
- 5. Same in 30 kg bags
- 293 bags
- Form boards (perimeter)
- 80 ft
- Form stakes
- 31 stakes
- Control-joint panels
- 4 panels (2 × 2)
- Joint spacing along the length
- 10 ft
- Joint spacing along the width
- 10 ft
- Joint depth (¼ of slab)
- 1 in
Order an exterior, air-entrained mix — ask the plant for a mix suited to freeze-thaw and de-icing salt.
Slope the base and slab 1–2% (⅛–¼ in per ft) away from the house: 2.4 in–4.8 in of fall across the width.
Load this example into the calculator
The layers, from the bottom up
- Dig out the lawn. Remove the sod and enough soil to fit the gravel base plus the slab, minus however far the finished slab will sit above the grass. Grade the bottom so it slopes away from the house, and compact it.
- Geotextile fabric (optional, worth it on clay). It stops the gravel from slowly pushing down into soft soil.
- Gravel base. Crushed ¾-in minus (“road base”), laid in 2–3 in (5–8 cm) layers and compacted with a plate compactor. This layer does most of the work preventing cracks and frost heave.
- Forms and rebar. 2×4 or 2×6 boards staked around the edge, set to your slope. Rebar sits on chairs so it ends up in the middle of the slab, not on the gravel.
- Concrete. Exterior air-entrained ready-mix, screeded, floated and broom-finished, with control joints cut to about a quarter of the slab’s depth.
dig depth = slab thickness + base thickness − height above grade
soil removed = area × dig depth × 1.25 (dug soil expands about 25%)
gravel base = area × base thickness × 1.25 (to allow for compaction)
concrete = area × slab thickness × (1 + waste %)
rebar = (bars each way × run length) × 1.1 ÷ 20 ft
joint spacing ≤ 2.5 × slab thickness (in) → feet
Before you start
- Check your municipality’s rules on front yards. Many Canadian cities limit how much of a front yard can be paved or covered with hard surfaces, and some require a permit or a drainage plan. In Metro Vancouver this varies a lot between municipalities, so call or check their bylaws first.
- Call before you dig (BC 1 Call in British Columbia, Ontario One Call, or Click Before You Dig elsewhere) to have gas, power and water lines marked. It’s free.
- Plan the soil disposal. A 20 × 20 ft patio produces over a dozen cubic yards of loose soil. That’s several large bin loads, and soil is heavy, so check the bin’s weight limit.
- Ready-mix trucks usually have a minimum charge for small loads, and need access to your yard. If the truck can’t reach, budget for a pump or a concrete buggy.
Where to buy in Metro Vancouver
Local suppliers we've checked. Nobody pays to be listed. Call ahead for prices, minimums and delivery to your area.
Ready-mix and small-load concrete
- Vancouver Ready Mix in Langley
Delivers across Metro Vancouver, with small loads and U-Cart concrete for pads and walkways.
- Yard At A Time Concrete in Delta
Mini trucks for tight residential sites; 1 yd³ minimum, up to about 2.4 m³ per load.
- Go Concrete in Surrey
Mixes on site, so you pay for what you pour. Serves the Lower Mainland.
Gravel, sand and soil (bulk)
- Meadows Landscape Supply in Pitt Meadows
Topsoil, bark mulch, gravel, sand, pavers and wall block, delivered across Greater Vancouver and the Fraser Valley.
- North Shore Landscape Supply Centre in North Vancouver
Road base, clear crush, soils and mulch, plus Belgard, Barkman and other wall block. Flat-fee delivery.
Related calculators
- Concrete Driveway Calculator
Enter your driveway's size to get the excavation, gravel base, rebar and ready-mix you'll need.
- Concrete Calculator
Enter your slab size and thickness to get the number of bags of concrete, or how much ready-mix to order.
- Gravel Calculator
Enter the area and depth to see how much gravel, sand, soil or mulch to order, in bulk or bags.
Last updated October 28, 2026