Concrete Calculator
Cubic yards and bags for slabs, footings, postsRuns in your browser
36.7 cubic feet = 1.36 cubic yards = 1.04 m³. Above about 1 cubic yard, ready-mix delivery is usually cheaper and faster than bags.
Rough material cost (cheapest option)
$231Ready-mix often has a short-load fee under 4–5 yd³. Rough 2026 US prices, edit to match local quotes.
Material estimates only. Round up, buy a little extra, and check with your supplier. Structural work (footings, framing, roofs) must follow local building codes; consult a licensed contractor where required.
How it works
Formulas
Slab volume (ft³) = length (ft) × width (ft) × thickness (in) ÷ 12Column volume (ft³) = π × (diameter (in) ÷ 24)² × height (ft)Cubic yards = cubic feet ÷ 271 cubic yard = 0.7646 m³.
Bags = cubic feet ÷ bag yieldTypical yields: 80 lb ≈ 0.60 ft³, 60 lb ≈ 0.45 ft³, 40 lb ≈ 0.30 ft³.
Worked example
Input: A 10 × 10 ft patio, 4 in thick, with 10% extra.
- 10 × 10 × 4 ÷ 12 = 33.3 ft³.
- Add 10%: 36.7 ft³ = 1.36 yd³.
- 80 lb bags: 36.7 ÷ 0.6 = 61.1 → 62 bags.
Result: 1.36 cubic yards, or 62 bags of 80 lb mix.
Limits
- Does not size rebar, mesh, gravel base or forms.
- Bag yields vary slightly by brand; check the bag.
How to use
- 1Choose slab, footing or round column / post hole.
- 2Enter the dimensions: length and width in feet, thickness in inches (or metric).
- 3Add 5–10% extra for uneven ground and spillage.
- 4Read the cubic yards to order or the number of bags to buy, and compare costs.
FAQ
How many 80 lb bags of concrete make a yard?
About 45. An 80 lb bag yields roughly 0.6 cubic feet and a cubic yard is 27 cubic feet, so 27 ÷ 0.6 = 45 bags (60 bags of 60 lb, 90 of 40 lb).
How thick should a concrete slab be?
4 inches is standard for patios, walkways and shed floors. Driveways usually need 5–6 inches, and anything carrying heavy vehicles more, with reinforcement. Check local code.
When should I order ready-mix instead of bags?
Above roughly 1 cubic yard, ready-mix is usually cheaper and much less work. Under 4–5 yards many suppliers add a short-load fee, so compare a quote with the bag price.
Can I use metric units?
Yes. Switch to Metric and enter meters and centimeters; results show cubic meters, square meters or tonnes alongside US units.