About Concrete Calculator
Calculate how much concrete you need for slabs, footings, columns, and stairs. Get cubic yards, cubic meters, and bag counts instantly. Free with no signup required.
How to use
- Select your pour shape: slab (patios, driveways, garage floors), footing (foundation footings, deck footings), column (posts, pillars), or stairs (concrete steps). Each shape uses different dimension inputs to calculate volume accurately.
- Enter the dimensions in feet and inches or metres. For slabs: length, width, and thickness (typically 4 inches for patios, 6 inches for driveways). For footings: length, width, and depth (typically 12 inches wide by 6 inches deep for residential). For columns: diameter and height.
- View the total concrete volume in cubic yards (the standard ordering unit in North America) and cubic metres. The calculator also shows the equivalent number of pre-mixed bags: 60-lb bags (yields 0.45 cu ft each) or 80-lb bags (yields 0.60 cu ft each) for smaller projects.
- Add the recommended waste factor. Always order 5-10% more concrete than calculated to account for spillage, uneven subgrade, and form bulging. For complex pours or irregular shapes, increase to 15%. Running short during a pour creates a cold joint that weakens the structure.
- Estimate material costs based on current local pricing. Ready-mix concrete in Canada typically costs $180-$250 per cubic yard delivered, with a minimum order of 1 cubic yard from most plants. Bagged concrete at hardware stores costs $5-$8 per 60-lb bag, making it economical only for projects under 0.5 cubic yards.
- Use the results to communicate with your concrete supplier. Provide the total cubic yards needed, the slump (workability) required, the strength specification (typically 25 MPa / 3,500 PSI for residential), and any additives needed (fibre mesh, air entrainment for freeze-thaw resistance).
Frequently asked questions
How many bags of concrete do I need for a 10x10 slab?
A 10-foot by 10-foot slab at the standard 4-inch thickness requires 1.23 cubic yards of concrete. In pre-mixed bags: approximately 56 bags of 80-lb concrete or 74 bags of 60-lb concrete. At 6-inch thickness (for driveways or heavy loads): 1.85 cubic yards, or 84 bags of 80-lb. For projects over 1 cubic yard, ordering ready-mix is significantly more economical and practical — mixing 56+ bags by hand is exhausting and risks inconsistent quality. Add 10% waste factor, bringing the 4-inch slab to about 62 bags of 80-lb or 1.35 cubic yards of ready-mix. First measure the area accurately with the
Square Footage Calculator before running the concrete estimate, especially for irregular shapes.
How do I calculate cubic yards of concrete?
Multiply length x width x thickness (all in feet), then divide by 27 (since there are 27 cubic feet in a cubic yard). Example: a 20 x 12 foot patio at 4 inches thick: 20 x 12 x 0.333 = 79.9 cubic feet / 27 = 2.96 cubic yards. For irregular shapes, break the area into rectangles and calculate each section separately, then sum the volumes. Always convert thickness from inches to feet first (4 inches = 0.333 feet, 6 inches = 0.5 feet). This calculator handles the conversions automatically.
How much extra concrete should I order?
Order 5-10% more than the calculated volume for standard rectangular pours. Increase to 10-15% for complex shapes, slopes, uneven subgrade, or first-time DIY projects. On a 3 cubic yard pour, 10% extra is 0.3 cubic yards — the cost of the extra concrete ($45-$75) is negligible compared to the cost of falling short and getting a cold joint in your slab, which creates a structural weak point that can crack and separate over time. Ready-mix plants typically charge a short-load fee if you order less than their minimum (usually 1 cubic yard), so slight over-ordering costs nothing extra.
What is the difference between concrete and cement?
Cement is one ingredient in concrete. Concrete is a mixture of cement (the binding agent, typically Portland cement), sand (fine aggregate), gravel or crushed stone (coarse aggregate), and water. The typical ratio by weight is roughly 10-15% cement, 60-75% aggregates, and 15-20% water. Cement alone is a powder that hardens when mixed with water through a chemical reaction called hydration. Pre-mixed bags contain all dry ingredients already blended — just add water. Ready-mix concrete arrives in a truck already mixed and ready to pour. You never use cement alone for structural applications.
How thick should a concrete slab be?
Thickness depends on the load the slab will bear. Standard residential applications: sidewalks and patios 4 inches (100 mm), driveways 5-6 inches (125-150 mm), garage floors 4-6 inches (100-150 mm with thickened edges), and shed foundations 4 inches. For heavy vehicle traffic or commercial applications, increase to 6-8 inches with reinforcement (rebar or wire mesh). Thicker slabs require proportionally more concrete — a 6-inch slab uses 50% more concrete than a 4-inch slab for the same area. Always place slabs on a compacted gravel base (4-6 inches) for proper drainage and frost protection.
How long does concrete take to cure?
Concrete reaches approximately 70% of its strength in 7 days and 99% in 28 days under normal conditions (20C/68F). You can walk on a slab after 24-48 hours, drive a car on a driveway after 7 days, and park heavy vehicles after 28 days. Keep the concrete moist during the first 7 days (cover with plastic or spray with water) because premature drying causes surface cracking and reduced strength. Temperature affects cure time: below 10C (50F), curing slows significantly. Below freezing, freshly poured concrete can be permanently damaged. Hot weather (above 30C) causes rapid moisture loss and requires additional precautions.
Do I need to reinforce a concrete slab?
Reinforcement is recommended for any slab subject to vehicle loads, heavy equipment, or frost heave conditions. Options include: welded wire mesh (WWM) placed in the middle third of the slab thickness for crack control, rebar (typically #4 bars on 18-24 inch centres) for structural loads, and fibre mesh mixed directly into the concrete for micro-crack control. A standard residential patio on stable soil may not require reinforcement, but a driveway always should. In Canadian climates with freeze-thaw cycles, reinforcement helps prevent the cracking that frost heave causes as the ground expands and contracts seasonally.
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