Concrete Calculator
Pick the shape, enter the dimensions, and get cubic yards, cubic feet, bag counts for every bag size, delivered weight and ready-mix cost — with your waste allowance already included.
Quick answer
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Dimensions
4 in typical, 5–6 in for vehicles
Identical pours
10% formed, 15% against soil
US average is roughly $140–$190
volume (ft³) = length x width x thickness/12 | yd³ = ft³ / 27 | order = volume x (1 + waste)
Order this much
Cubic yards to order
1.36yd³
Ready-mix rounds to 1.5 yd³
Cubic feet
36.7cu ft
Weight
2.75tons
5,500 lb
Ready-mix material cost
$248
Before delivery and short-load fees
Bags of mix
| Bag | Yield | Bags | Total weight |
|---|---|---|---|
| 40 lb | 0.3 ft³ | 123 | 4,920 lb |
| 50 lb | 0.375 ft³ | 98 | 4,900 lb |
| 60 lb | 0.45 ft³ | 82 | 4,920 lb |
| 80 lb | 0.6 ft³ | 62 | 4,960 lb |
How this calculator works
Every shape here is solved as geometry, then converted. A slab or footing is a rectangular prism, a pier is a cylinder (pi x r² x h), stairs are a stacked series where each step carries one more riser of depth than the one above it, and a post hole is the hole volume minus the volume the post itself displaces — which is why a 4x4 in a 12 inch hole takes noticeably less concrete than the hole's full volume.
Bag counts divide the ordered volume by the yield printed on the bag: 0.60 ft³ for 80 lb, 0.45 ft³ for 60 lb, 0.375 ft³ for 50 lb and 0.30 ft³ for 40 lb. Weight uses 150 lb per cubic foot, the standard unit weight of normal-weight concrete, so one cubic yard is about 4,050 lb.
Ready-mix is rounded up to the next quarter yard because that is how trucks are batched and billed. Below the plant's truck minimum — usually 3 to 5 yards — expect a short-load fee; the slab cost calculator models that against bagged mix.
Source & method: Geometry and unit conversions computed in your browser. Bag yields are the nominal values published by US bagged-mix manufacturers; unit weight is 150 lb/ft³ for normal-weight concrete. Nothing on this page reproduces a copyrighted code table.
Forming and finishing supplies
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- Form stakes (24 in steel)4 in slabHold form boards to line and grade against the pressure of wet mix.Check price
- Expansion joint stripIsolate the slab from footings, walls and adjoining concrete.Check price
- Vapor barrier (6 mil poly)Required under interior slabs and worth it under any garage floor.Check price
- Concrete cure and sealHolds moisture in for the first week so the slab reaches strength.Check price
Pour-day tools
Links below are affiliate links. If you buy through them we may earn a commission at no extra cost to you.
- Magnesium bull floatFlattens and closes the surface right after screeding.Every slab · Check price
- Screed board / power screedStrikes the slab to grade before it starts to set.Slabs · Check price
- Concrete mixer (1.5–4 cu ft)Faster and more consistent than mixing bags in a wheelbarrow.Bagged pours · Check price
- Contractor wheelbarrow6 cu ft steel tray moves roughly 300 lb of wet mix per trip.Every pour · Check price
- Edger, groover and steel trowelRadius the edges and cut control joints before the slab hardens.Finishing · Check price
- Rubber boots and nitrile glovesWet concrete is caustic — cover skin before you stand in it.Safety · Check price
Frequently asked questions
- How do I calculate how much concrete I need?
- Multiply length by width by thickness with every dimension in feet, which gives cubic feet, then divide by 27 to get cubic yards. For a 4 inch slab use 0.333 ft as the thickness. Add 5 to 10 percent for subgrade variation and spillage.
- How many cubic feet are in a cubic yard of concrete?
- 27 cubic feet. A cubic yard weighs about 4,050 lb at the standard 150 lb per cubic foot unit weight of normal-weight concrete.
- How much extra concrete should I order?
- Order 10 percent over the calculated volume on a formed slab and 15 percent on footings poured against soil, where the trench is never exactly the width you dug. Running short mid-pour creates a cold joint you cannot undo.
- How thick should a concrete slab be?
- 4 inches is standard for patios, walkways and shed floors. Use 5 to 6 inches where vehicles park and 6 inches for a driveway carrying trucks. Your local code governs footing depth, which is tied to frost depth.
- How many bags of concrete make a yard?
- 45 bags of 80 lb mix, 60 bags of 60 lb mix, or 90 bags of 40 lb mix, using the published yields of 0.60, 0.45 and 0.30 cubic feet per bag.
Related calculators & charts
- Concrete Slab Cost CalculatorReady-mix versus bagged cost for a slab, including delivery and short-load fees.
- Concrete Bag CalculatorHow many 40, 50, 60 or 80 lb bags a pour needs, by published bag yield.
- Post Hole Concrete CalculatorConcrete per hole and per fence run, with the post volume subtracted.
- Cubic Yard CalculatorConvert any length, width and depth into cubic yards, feet and tons.
- Gravel CalculatorTons and cubic yards of gravel, crushed stone or road base for any area.
- Sand CalculatorBedding, paver and fill sand quantities by volume, weight and bag count.