Concrete Calculator
Order ready-mix by the cubic yard. Enter any rectangular pour — slab, footing strip, or pad — to get volume in cubic yards and cubic feet, with waste and an optional per-yard cost. For bag counts use the Concrete Bag Calculator; for patio slabs with a bag comparison use the Concrete Slab Calculator.
Enter your measurements to see what to buy.
Next step for your project
- Compare bag counts and yieldsExact counts for 40/50/60/80-lb bags using your bag label’s yield.
- Plan the gravel baseEstimate the compacted base that goes under the slab.
- Open the patio plannerGet concrete + gravel base in one combined shopping list.
- Read the 10×10 slab guideWorked walkthrough for a standard patio or shed slab.
How to calculate it
Order ready-mix by the cubic yard. Enter any rectangular pour — slab, footing strip, or pad — to get volume in cubic yards and cubic feet, with waste and an optional per-yard cost. For bag counts use the Concrete Bag Calculator; for patio slabs with a bag comparison use the Concrete Slab Calculator.
Source: Volume = length × width × thickness; 1 cubic yard = 27 cubic feet (standard ready-mix convention).
A 10×10 ft patio slab at 4 in thick: 10 × 10 × (4÷12) = 33.33 ft³ ÷ 27 = 1.23 yd³. With 10% waste: 1.36 yd³ to order.
Want the full step-by-step walkthrough? Read our How to Plan and Pour a Concrete Patio Slab.
Concrete bag yields & coverage
When a pour is too small for ready-mix, bagged mix is the practical choice. This table shows the yield of each common bag size and how much area one cubic yard covers at typical slab thicknesses.
| Bag size | Yield per bag | Bags per cubic yard | Coverage at 4 in deep |
|---|---|---|---|
| 40 lb | 0.30 ft³ | ~90 bags | 0.9 ft² |
| 60 lb | 0.45 ft³ | ~60 bags | 1.35 ft² |
| 80 lb | 0.60 ft³ | ~45 bags | 1.8 ft² |
One cubic yard covers 81 ft² at 4 in deep, 65 ft² at 5 in, and 54 ft² at 6 in. Yields follow typical manufacturer-published values (Quikrete/Sakrete) — confirm on the bag label.
How to use this calculator
- Enter the length and width of your pour in feet and inches — the paired boxes let you type 10 ft 6 in without converting.
- Set the depth (thickness) in inches: 4 in for patios and walkways, 5–6 in for driveways.
- Leave the waste allowance at 10% for a typical formed pour, or raise it for uneven ground.
- Optionally enter your local ready-mix price per cubic yard for a material cost estimate.
Purchasing & waste guidance
- A standard patio or sidewalk slab is 4 in thick; driveways are usually 5–6 in.
- Add about 10% extra for spillage, uneven subgrade and over-excavation.
- One cubic yard of concrete weighs roughly 4,000 lb — anything over about 1 yard is usually cheaper as ready-mix delivery.
- For small pours under a yard, use the Concrete Bag Calculator instead.
Waste factor guidance
- Keep 10% for flat, formed pours on a prepared base — it covers spillage and minor over-excavation.
- Raise to 15% for uneven subgrade, many form corners, or hand-mixing where spillage is higher.
- Lower to 5% only for large, simple, machine-finished slabs on a laser-graded base.
Common mistakes to avoid
- Measuring thickness in feet instead of inches — the depth field is in inches, so enter 4 not 0.33.
- Forgetting that ready-mix is ordered by the full cubic yard — always round up, never down.
- Using footprint area alone without multiplying by thickness, which gives square feet instead of volume.
Assumptions & what’s included
- Slab is a single rectangular pour.
- Waste allowance covers spillage, uneven subgrade and minor over-excavation.
- Price is per cubic yard of ready-mix and is optional — enter your local quote for a cost estimate.
Sources & references
- Bag yields (40 lb ≈ 0.30, 60 lb ≈ 0.45, 80 lb ≈ 0.60 ft³) follow published product data from Quikrete and Sakrete premixed concrete technical data sheets.
- Ready-mix volume convention: 1 cubic yard = 27 cubic feet (ACI standard practice for ordering concrete).
- Slab thickness guidance (4 in patios, 5–6 in driveways) follows common residential building practice; confirm structural slabs with your local building code.
Learn more about how every calculator works on our methodology page.
Frequently asked questions
How many cubic yards of concrete do I need for a 10×10 slab?
A 10×10 ft slab at 4 in thick needs about 1.23 yd³ before waste, or roughly 1.36 yd³ with a 10% waste allowance. Round up to 1.5 yards when ordering ready-mix.
How thick should a concrete slab be?
4 in is standard for patios, walkways and shed pads. Driveways that carry vehicle traffic are typically 5–6 in. Footings and structural slabs should follow your local building code or an engineer’s spec.
Should I order ready-mix or use bags?
Bagged mix makes sense for small pours under roughly 1 cubic yard. Above that, delivered ready-mix is usually cheaper and far less labor. Use the Concrete Bag Calculator to compare.
How do I convert cubic feet to cubic yards?
Divide cubic feet by 27, since one cubic yard equals 27 cubic feet. A 10×10 ft slab at 4 in thick is 33.33 ft³, which is 1.23 yd³ before waste.
How do I calculate concrete for fence posts?
Treat each post hole as a cylinder: π × (hole radius)² × depth, then multiply by the number of posts. A 4×4 post in an 8 in wide × 24 in deep hole needs about 0.7 ft³, or roughly two 80-lb bags. For a full fence line, use the Post Hole Concrete Calculator.
What is the difference between cubic feet and cubic yards?
A cubic yard is 27 cubic feet — a 3×3×3 ft cube. Concrete volume is computed in cubic feet (length × width × thickness) and then divided by 27 to get the cubic yards ready-mix is ordered by.
How much does a cubic yard of concrete weigh?
A cubic yard of cured concrete weighs roughly 4,000 lb (2 tons). That is why pours over about a yard are almost always delivered by ready-mix truck rather than mixed by hand.
Related guides
Step-by-step project guides that use this calculator.