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; city rules for driveways set a minimum, 4 in in some towns and 6 in others. Your plan and local code have 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) Supplier order increment (cu yd) The step the plant sells in, often a quarter or half yard: ask when you order. Gravel base under it The thickness of compacted gravel your plan puts under the slab or footing. Your concrete price per cu yd ($) Truck delivery fee ($) Small-load fee ($) Your price per bag ($) 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 112 of 50 lb · 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

At posted store prices

$454.30 70 × $6.49 a bag, QUIKRETE Concrete Mix 1101, 80 lb at Cole’s Hardware in central Pennsylvania on Oct 13, 2026

$454.30 for this item, before tax and delivery.

Each price is one store’s posted price on the day shown, for the product named. Prices vary between stores: check yours. Your own price goes under Details.

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 · 112 of 50 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, delivery and small-load fees, and type them with your bag price under Details to compare. 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

Before the truck comes

Ready-mix starts to set once it is mixed, so the job has to be ready when the truck backs in. Tick each line as it is done.

Forms staked and braced at the finished height, and the base compacted and firm
Utilities marked before any digging: call 811 a few working days ahead
The order: yards with your extra, the strength your plan names, and whether the plant adds fibers or an accelerator in cold weather
The plant’s minimum, order increment, small-load fee and the free unloading time before waiting time is charged
A route the truck can drive: it is heavy enough to crack a driveway or sidewalk and must stay off a septic tank and drain field
Where the chute reaches, and wheelbarrows or a pump booked for the rest
Helpers and tools on site: rakes, a screed board, a bull float, an edger, a groover, and a hose for the chute
Ground that is not frozen, and plastic sheeting or curing compound to keep the slab moist for the first days

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

Which bag mix?

QUIKRETE’s four bagged concrete mixes, from their data sheets. Every one of these makes the same volume for the same bag weight: 0.60 cu ft for 80 lb, 0.45 for 60 lb, 0.375 for 50 lb and 0.30 for 40 lb, so the bag count above holds for any of them. The strength your slab or footing needs comes from your plan or your local code.

QUIKRETE bagged concrete mixes compared
Mix	Strength at 28 days	Sooner	What it is for	Bags
Concrete Mix (No. 1101)	4,000 psi	2,500 psi at 7 days	The everyday mix for slabs, footings, steps, walks and post footings, 2 in thick or more	40, 50, 60 and 80 lb
5000 High Early Strength (No. 1007)	5,000 psi	1,500 psi at 1 day; walk on it after 10 to 12 hours	Gains strength fast, which suits cold weather and a slab you need back soon	50, 60 and 80 lb
Crack Resistant (No. 1006)	4,000 psi	2,500 psi at 7 days	Synthetic fibers for less shrinkage cracking, and air entrained to stand up to freezing and thawing	50, 60 and 80 lb
Fast-Setting (No. 1004)	4,000 psi	Sets in 20 to 40 minutes; 1,000 psi at 24 hours	Poured dry into a post hole and soaked: two 50 lb bags set a 3 in post in a 9 in hole 30 in deep. Wait 4 hours before loading the post or walking on a slab	50 and 60 lb

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?

Paths and patios are usually 4 inches thick, and a shed base 4 to 6 inches, by the load it bears. A floor slab in a house must be at least 3 1/2 inches under the International Residential Code. Driveways follow your city’s minimum: at least 4 inches in some towns, 6 in others. At 4 inches, one cubic yard covers 81 square feet.

Source: QUIKRETE project instructions: concrete sidewalks and small slabs, pouring and finishing concrete slabs, and building a concrete patio; International Residential Code 2021, R506 Concrete floors (on ground); City driveway rules: Des Plaines, Illinois (residential driveway permit guide), Newark, Delaware (driveway and private walkway specifications) and Davison, Michigan (concrete technical specification). Listed on the Sources page.

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.

Which bagged concrete should I use?

For most slabs, footings and steps, a standard 4,000 psi mix such as QUIKRETE Concrete Mix. Choose a high early strength mix (5,000 psi, walk on it after 10 to 12 hours) for cold weather or a slab you need back soon, a fiber mix to cut shrinkage cracking, and a fast-setting mix for fence posts. A bag of the same weight makes the same volume whichever you choose; your plan or code sets the strength.

Source: QUIKRETE data sheets: 5000 High Early Strength Concrete Mix No. 1007, Crack Resistant Concrete Mix No. 1006 and Fast-Setting Concrete Mix No. 1004. Listed on the Sources page.

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 September 2026 than a year earlier (Bureau of Labor Statistics producer price index, preliminary).

Every building material we track, month by month, with the change in a year.

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.