Concrete Calculator

Cubic yards = length × width × thickness in feet ÷ 27: a 12 × 10 ft slab 4 inches thick is 1.48 cubic yards, 1.56 with 5% extra, or 70 bags of 80 lb.

Your measurements

Example

Use the unit shown for each box, or type another one: 12 ft 6 in, 150 in, 3.8 m and 600 mm all work, as do the marks on a tape measure.

Shape Length (ft) Width (ft) Thickness Most patios and walks are 4 in thick and driveways 5 to 6 in. Your local code has the final word. Identical sections or holes

Details Package sizes, prices and materials

Extra concrete (%) Bag example Yield per bag (cu ft) Change this to the yield on your mix. Supplier minimum order (cu yd) Your concrete price per cu yd ($) Supplier order increment (cu yd)

Example: replace these measurements

Your material list

70 bags of 80 lb

1.56 cubic yards of concrete

Or 94 bags of 60 lb, or 140 of 40 lb. Includes your 5% extra; 1.48 cu yd before extra.

Your measured layout

Length and width run across the slab; thickness goes down through it. This measures quantity, not a recommended slab design.

Your shopping list

70 bags of 80 lb

Quantities and package details

Before extra: 1.4815 cu yd (40 cu ft)
With your allowance: 42 cu ft
Cubic meters: 1.1893
Bags of 80 lb: 70
Same pour in other bags: 94 of 60 lb · 140 of 40 lb
Weight of the bags: 5,600 lb (2.8 US tons)
Edge forms: 44 ft of form boards, as deep as the pour

Bags or a truck: 70 bags of 80 lb weigh 2.8 tons to lift and mix by hand. A ready-mix truck brings it mixed; ask the plant for its price per yard and its small-load fee, then compare. Delivery, pumping and waiting time are charged on top.

The calculation

12 × 10 × 0.3333 = 40 cu ft per rectangle
40 × 1 identical shapes = 40 cu ft
40 × (1 + 5/100) ÷ 27 = 1.5556 cu yd
Edge forms: 2 × (12 + 10) = 44 ft

Not measured yet? Common jobs

A rough starting point, worked out with this calculator. Usual sizes and thicknesses; your plan and local code have the final word. 5% extra, 80-lb bags. Use a row to load its size into the calculator, then change it to your measurements.

Concrete for common home jobs
Job	Size	Cubic yards	80-lb bags	Bags or truck
Fence post hole	10 in wide, 3 ft deep	0.06	3	Bags
AC or generator pad	3 × 3 ft, 4 in	0.12	6	Bags
Walkway	3 × 20 ft, 4 in	0.78	35	Bags
Shed slab	10 × 12 ft, 4 in	1.56	70	Either
Patio	12 × 12 ft, 4 in	1.87	84	Either
One-car driveway	12 × 20 ft, 5 in	3.89	175	Truck
Two-car garage floor	20 × 20 ft, 4 in	5.19	234	Truck

Common questions

How many bags of concrete make a cubic yard?

45 bags of 80-lb QUIKRETE Concrete Mix, 60 bags of 60 lb or 90 bags of 40 lb. A cubic yard is 27 cubic feet, and QUIKRETE gives 0.60, 0.45 and 0.30 cubic feet per bag.

Source: QUIKRETE Concrete Mix No. 1101 data sheet. Listed on the Sources page.

How much concrete do I need for a 10 × 10 slab 4 inches thick?

About 1.23 cubic yards before any extra: 10 × 10 × 4 ÷ 12 = 33.3 cubic feet, divided by 27. With 5% extra that is about 1.3 cubic yards, or 59 bags of 80 lb.

Source: QUIKRETE Concrete Mix No. 1101 data sheet. Listed on the Sources page.

How thick should a concrete slab be?

Most patios, walks and shed slabs are poured 4 inches thick, and driveways 5 to 6 inches. Your plan and local code have the final word. At 4 inches, one cubic yard covers 81 square feet.

How much gravel goes under a slab?

Many patios and walks sit on about 4 inches of compacted gravel; the ground and your plan decide. Measure the base as its own layer: 4 inches under a 10 × 10 ft slab is about 1.2 cubic yards of gravel.

Should I order ready-mix or bags?

Under about a cubic yard, bags; at two yards or more, a truck. In between, compare the two: a yard takes 45 bags of 80 lb, 3,600 lb to lift and mix by hand. Ready-mix plants add a fee for small loads, so ask for it with the price per yard. The result box says which side your pour falls on.

How to plan the quantity

Slabs, footings, walls and curbs use rectangular volume: length × width or wall height × thickness. Thickness is in inches. Columns and post holes use solid circular area × height; tube mode can subtract an inner diameter. Multiply identical sections without re-entering their measurements.

Tube volume uses the circular area, subtracting an inner circle for a hollow tube. Steps mode assumes solid steps on a level base: width times tread depth times riser height times the sum of the step numbers.

The extra percentage is your ordering choice. Enter the bag yield from your mix, or ask a ready-mix supplier about their minimum, delivery charge and order increment.

Before you order

This measures concrete only. It does not specify thickness, reinforcement, base preparation, drainage, strength or curing.
The steps model is solid, not a stair shell. Footing dimensions must come from the design and local ground conditions.

Have prices moved?

Ready-mixed concrete cost 2.3% more in August 2026 than a year earlier (Bureau of Labor Statistics producer price index, preliminary).

What owners paid: the typical driveway and walkway job cost $2,914 in the 2023 Census survey.

Plan the work as well as the order: How to pour a concrete slab: mix, finish and cure.

Before ordering, read the guide: How much concrete do I need? Yards, bags and when to order a truck. Or choose another calculator.