Concrete Calculator
Slabs, footings, columns, circular slabs and stairs — in any unit you like.
This is a complete concrete calculator built for real job-site math. Pick a shape, enter your dimensions in feet, inches, yards, meters or centimeters, choose a waste factor, and instantly get cubic feet, cubic yards, cubic meters, 60 lb and 80 lb bag counts, estimated weight and estimated material cost — everything you need to order the right amount of concrete the first time.
Watch: How to Use the Concrete Calculator
Watch this short tutorial to learn how to enter slab dimensions, add a waste allowance, and read concrete volume, bag, weight, and cost estimates.
Your Estimate
Cubic Feet
36.67 ft³
Cubic Yards
1.36 yd³
60 lb Bags
82
80 lb Bags
62
Estimated Weight
5500 lb (2.75 tons)
Estimated Material Cost
$203.70
Estimate only — waste factor already applied. Confirm exact quantities with your ready-mix supplier.
Results Actions
Common Concrete Depths and Thicknesses
Formula Explanation
Slab / Footing / Circular Slab
Rectangular volume = Length × Width × Thickness. Circular volume = π × (Diameter ÷ 2)² × Thickness. All dimensions are converted to feet first, giving cubic feet, then divided by 27 for cubic yards.
Column
Volume = π × (Diameter ÷ 2)² × Height × Quantity. This treats each column as a cylinder and multiplies by how many identical columns you're pouring.
Stairs
Solid concrete stairs stack like a set of shrinking rectangular blocks — the bottom step spans the full run, and each step above it is one tread shorter. Volume = Width × Rise × Run × [N × (N + 1) ÷ 2], where N is the number of steps. This triangular-number formula accounts for the full solid mass under every tread.
Step-by-Step Instructions
- 1Choose the shape that matches your pour: slab, footing, column, circular slab, or stairs.
- 2Measure your dimensions and enter each one — pick whichever unit (ft, in, yd, m, cm) is easiest to measure in.
- 3Select a waste factor. Use 5% for simple, well-prepped pours and 10-15% for uneven ground or complex shapes.
- 4Enter your local price per cubic yard if you want an estimated material cost.
- 5Read your results: cubic feet, cubic yards, cubic meters, bag counts and total weight update instantly.
- 6Use the cubic yard figure to place your ready-mix order, or the bag counts if you are hand-mixing or using a mixer.
Real Examples
Example 1 — Backyard Patio Slab
A 12 ft x 16 ft patio at 4" thick: 12 × 16 × (4/12) = 64 cubic feet → 64 / 27 = 2.37 cubic yards. Adding 10% waste brings it to about 2.6 cubic yards, or roughly 118 bags of 80 lb concrete if hand-mixed.
Example 2 — Deck Footings
Eight round footings, each 12" diameter and 36" deep: volume per footing = π × 0.5² × 3 = 2.36 cubic feet. Eight footings = 18.85 cubic feet → 0.70 cubic yards. Most suppliers will round this up to a 1 yard minimum order.
Example 3 — Circular Fire Pit Pad
A circular pad 8 ft across and 4" thick: π × 4² × (4/12) = 16.76 cubic feet → 0.62 cubic yards, or about 28 bags of 60 lb concrete.
Example 4 — Concrete Stairs
A 4-step staircase, 3.5 ft wide, with a 7" rise and 11" run per step: 3.5 × (7/12) × (11/12) × (4×5/2) = 3.5 × 0.583 × 0.917 × 10 ≈ 18.7 cubic feet, or about 0.69 cubic yards.
Accuracy & Assumptions
- Results are estimates only and are meant for planning purposes.
- Bag yields, mix designs and material weights can vary by manufacturer and supplier.
- Consider ordering an additional 5–10% for spillage and uneven subgrade.
- Verify all slab, footing or column measurements before purchasing concrete.
- Check local building codes and consult a structural engineer for load-bearing pours.
Frequently Asked Questions
How much concrete do I need for a 10x10 slab?
For a 10 ft x 10 ft slab at a standard 4" thickness, you need about 1.23 cubic yards of concrete (100 sq ft x 0.333 ft ÷ 27). Add 5-10% waste and most contractors round up to 1.5 cubic yards to be safe.
How many 80 lb bags of concrete make a yard?
It takes roughly 45 bags of 80 lb pre-mixed concrete to make one cubic yard, since each 80 lb bag yields about 0.6 cubic feet and a cubic yard is 27 cubic feet (27 ÷ 0.6 ≈ 45).
How many 60 lb bags of concrete make a yard?
You need about 60 bags of 60 lb pre-mixed concrete to make one cubic yard. Each 60 lb bag yields roughly 0.45 cubic feet (27 ÷ 0.45 = 60).
How much does concrete weigh per cubic yard?
Standard concrete weighs approximately 150 lb per cubic foot, or about 4,050 lb (just over 2 tons) per cubic yard once cured.
Should I order ready-mix or use bagged concrete?
For pours over 1 cubic yard, ready-mix delivery is almost always cheaper and more consistent than bagged concrete. Bagged concrete makes sense for small jobs like fence posts, footings, or repairs under 1 cubic yard.
How much extra concrete should I order for waste?
Most professionals add 5-10% extra for uneven subgrade and spillage. Complex shapes, hand-mixing, or difficult site access justify the higher 15% waste factor.
Common Mistakes to Avoid
- Forgetting to convert inches to feet before multiplying — thickness is almost always measured in inches but volume math needs feet.
- Not accounting for waste factor, then running short mid-pour and having to order a rushed, expensive small batch.
- Measuring only the visible slab area and ignoring thickened edges, footings, or turndowns that need extra concrete.
- Assuming all bagged concrete yields the same volume — 40 lb, 60 lb and 80 lb bags all cover different cubic footage.
- Ignoring rebar, gravel base, or vapor barrier costs when budgeting — concrete is only one line item in a slab project.
- Ordering ready-mix without checking the supplier's minimum yardage — many trucks have a 1 yard minimum plus a short-load fee.
Tips for Ordering Concrete
- Ready-mix trucks are priced per cubic yard and usually have a minimum load (often 1 yard) plus a short-load fee below that — combine small pours where possible.
- Order 5-10% more concrete than your raw calculation to cover subgrade irregularities, spillage, and formwork variance.
- Schedule your pour for cool, calm weather when possible — extreme heat accelerates curing and can cause cracking.
- Have extra hands and tools (screed, float, edger) ready before the truck arrives — ready-mix concrete starts setting fast.
- For structural elements (footings, columns, load-bearing slabs) confirm mix strength (PSI) and rebar schedule with a structural engineer.
- Ask your supplier about fiber-reinforced or air-entrained mixes if your slab will face freeze-thaw cycles or heavy vehicle loads.
This calculator provides an estimate for planning purposes only. Material needs vary by site conditions, waste and supplier specifications — always confirm final quantities with your contractor or supplier before purchasing, and consult a structural engineer for load-bearing work.