Concrete Calculator

Find the cubic yards of concrete for a slab, footing, wall or column, the bags, the weight and the cost, with an extra for waste.

Free to use
No sign-up
Numbers stay in your browser

Last updated: 3 November 2026

Find the Concrete for a Slab, Footing or Wall

Currency symbol

Concrete to order

1.36 cubic yards

Your slab (10 ft × 10 ft, 4 in thick) comes to 1.23 cubic yards. With 10% extra for waste, order about 1.36 cubic yards.

To order (with extra)1.36 yd³
Exact volume1.23 yd³
Cubic feet36.67 ft³
Weight5,494 lb
80 lb bags62
Area100 sq ft

Bags of dry mix to buy

Bag size	Bags needed
40 lb bag	123
50 lb bag	98
60 lb bag	82
80 lb bag	62

The working: 10 × 10 × (4 ÷ 12) = 33.33 ft³, ÷ 27 = 1.23 yd³, then + 10% for waste = 1.36 yd³

Bag yields are typical figures, so check the label of the bag you buy. Order a little extra, because uneven ground and spillage use more than the plan shows.

About Concrete Calculator

Concrete is sold by the cubic yard, or by the cubic meter, and in bags for small jobs. Multiply the length, width and thickness to get the volume, then add a little extra for waste.

The Formula

Cubic Yards =L × W × T27

L = length (ft)
W = width (ft)
T = thickness (ft), so inches ÷ 12
27 = cubic feet in a cubic yard

Multiply by how many you are pouring, then add a little extra for waste.

Order Smart

Add 5 to 10% for waste and uneven ground
Bags suit small jobs, and ready-mix suits bigger pours
Split odd shapes into rectangles and add them up
Ask your supplier about delivery minimums

Bags per Cubic Yard

How much one bag of dry mix makes, and how many bags fill a cubic yard.

Bag size	One bag makes	In cubic yards	Bags per yd³
40 lb bag	0.3 ft³	0.0111 yd³	90
50 lb bag	0.375 ft³	0.0139 yd³	72
60 lb bag	0.45 ft³	0.0167 yd³	60
80 lb bag	0.6 ft³	0.0222 yd³	45

An 80 lb bag makes 0.6 cubic feet. Always check the yield printed on the bag you buy.

What Does Concrete Weigh?

Normal ready-mixed concrete weighs about 150 lb per cubic foot, or 2,400 kg per cubic meter.

Amount	Pounds	Kilograms
1 cubic foot	150 lb	68 kg
1 cubic yard	4,045 lb	1,835 kg
1 cubic meter	5,291 lb	2,400 kg

Reinforced and lightweight concrete weigh a little more or less, so treat this as a typical figure.

Cubic Yards for Common Slabs

Concrete for popular slab sizes at three thicknesses, before any extra for waste. Click a size to open it in the calculator.

Area	4 in	5 in	6 in
100 sq ft	1.23 yd³	1.54 yd³	1.85 yd³
120 sq ft	1.48 yd³	1.85 yd³	2.22 yd³
144 sq ft	1.78 yd³	2.22 yd³	2.67 yd³
240 sq ft	2.96 yd³	3.7 yd³	4.44 yd³
400 sq ft	4.94 yd³	6.17 yd³	7.41 yd³
576 sq ft	7.11 yd³	8.89 yd³	10.67 yd³
900 sq ft	11.11 yd³	13.89 yd³	16.67 yd³

Volume = length × width × thickness ÷ 27.

Cubic Yards by Thickness

How much concrete a given area takes, and how far one cubic yard goes.

Thickness	100 sq ft	1,000 sq ft	1 yd³ covers
3 in	0.93 yd³	9.26 yd³	108 sq ft
4 in	1.23 yd³	12.35 yd³	81 sq ft
5 in	1.54 yd³	15.43 yd³	64.8 sq ft
6 in	1.85 yd³	18.52 yd³	54 sq ft
8 in	2.47 yd³	24.69 yd³	40.5 sq ft

Volume = area × thickness ÷ 27, with the thickness in feet.

Column and Tube Sizes

Concrete for each foot of depth of a round column, tube form or post hole. Click a diameter to open it in the calculator.

Cubic feet	Cubic yards	80 lb bags
0.349 ft³	0.0129 yd³	0.58
0.545 ft³	0.0202 yd³	0.91
0.785 ft³	0.0291 yd³	1.31
1.396 ft³	0.0517 yd³	2.33
1.767 ft³	0.0654 yd³	2.95
3.142 ft³	0.1164 yd³	5.24

Per foot of depth. Multiply by the depth and the number of holes.

Cement, Sand and Gravel

If you mix it yourself, here is what one cubic yard of concrete takes for three common mixes (cement : sand : gravel, by volume).

Mix	Cement (94 lb bags)	Sand	Gravel
1:2:4	5.9	0.44 yd³	0.88 yd³
1:1.5:3	7.6	0.42 yd³	0.84 yd³
1:2:3	6.9	0.51 yd³	0.77 yd³

Estimates: the dry materials take up about 1.54 times the volume of the wet concrete, and a 94 lb bag of cement is about 1 cubic foot. Real mixes vary.

Try an Example

Pick one to fill in the calculator and see its answer.

Example	To order
	1.36 yd³
	5.43 yd³
	4.89 yd³
	8.15 yd³
	0.128 yd³
	95 blocks

Each includes 10% extra for waste (5% for the block wall).

How It Works

1Choose what you are pouring. A slab, driveway, footing or wall, a round column or hole, or a block wall.
2Enter the sizes. Length and width in feet, and the thickness in inches. Add some extra for waste.
3Read the answer. Cubic yards to order, bags, weight and cost, with the working shown.

Good to know

Measure the length and width in feet and the thickness in inches. The calculator turns inches into feet for you.
Round the order up, because concrete is sold in whole or half cubic yards, and the plan never includes spillage.
Bags are rounded up to whole bags, and a bag's yield is a typical figure, so check the label.
Slab thickness depends on the use and your local code, so ask a builder or your building office.

What is included

Cubic yards or cubic meters for a slab, footing or wall
Round columns, tube forms, post holes and piers
40, 50, 60 and 80 lb bags (or 20, 25 and 40 kg)
Weight, extra for waste and the cost
Cement, sand and gravel if you mix it yourself
Concrete blocks for a wall, tables, copy link and print

Important to know

Your numbers stay in your own browser and are never sent anywhere. This is an estimate for planning, so ask a builder or your concrete supplier before you order, especially for structural work such as footings and foundations.

Use this free concrete calculator to find how many cubic yards of concrete you need for a slab, pad, driveway, sidewalk, footing, wall, floor, column or post hole. Enter the sizes and an extra for waste, and you get the concrete to order, the number of 40, 50, 60 and 80 lb bags, the weight and, if you add a price, the cost. Switch to metric for cubic meters. Pick a mix such as 1:2:4 to see the cement, sand and gravel for mixing it yourself, or use the Concrete Blocks tab to count the blocks for a wall. Every answer shows the working, and tables list bags per cubic yard, common slab sizes, column sizes and what concrete weighs. It is free and instant, and your numbers stay in your browser.

How to work out how much concrete you need

Concrete is sold by volume, in cubic yards in the US and cubic meters elsewhere. Work out the volume of the space you are filling, then add a little extra for waste. For a slab, footing or wall the volume is length × width × thickness. Measure the length and width in feet and the thickness in inches, turn the inches into feet by dividing by 12, and divide the cubic feet by 27 to get cubic yards.

Example: a slab 10 ft long, 10 ft wide and 4 in thick
10 × 10 × (4 ÷ 12) = 33.33 cubic feet
33.33 ÷ 27 = 1.23 cubic yards
With 10% extra for waste you would order about 1.36 cubic yards.

Slabs, driveways, sidewalks and floors

All of these are flat slabs, so the same formula works. A 20 ft by 20 ft slab that is 4 in thick is 4.94 cubic yards, and a 12 ft by 24 ft driveway that is 5 in thick is 4.44 cubic yards, before any extra. Many patios and sidewalks are about 4 inches thick and driveways are often thicker, but the right thickness depends on the use, the ground and your local building rules, so check with a builder.

Footings and walls

A footing is a long, narrow slab, so enter its length, its width and its depth. A footing 100 ft long, 2 ft wide and 12 in deep is 100 × 2 × 1 = 200 cubic feet, or 7.41 cubic yards. For a wall, use the wall length, its height as the width, and its thickness. Footings and foundations carry the weight of a building, so ask a builder or engineer for the sizes before you pour.

Round columns, piers and post holes

A round column, tube form, pier or post hole is a cylinder: π × (diameter ÷ 2)² × height. A hole 12 in across and 4 ft deep takes π × 0.5² × 4 = 3.14 cubic feet, or 0.116 cubic yards. Enter how many you need and the calculator multiplies for you. The table of column and tube sizes shows the concrete for each foot of depth.

How many bags of concrete mix?

Divide the volume by what one bag makes, and round up to whole bags. An 80 lb bag makes about 0.6 cubic feet, a 60 lb bag 0.45 and a 40 lb bag 0.3, so a cubic yard takes about 45 bags of 80 lb, 60 bags of 60 lb or 90 bags of 40 lb. For the 10 ft by 10 ft slab above with 10% extra, that is 62 bags of 80 lb. Bag yields are typical figures, so check the label of the bag you buy.

Bags or ready-mix?

Bags are handy for small jobs such as a few post holes or a small pad, because you can mix a little at a time. For larger pours, ready-mixed concrete delivered by truck is usually easier, because mixing dozens of bags by hand is slow and the batches can differ. Ask your supplier about delivery minimums and how much a truck carries, and enter a price per cubic yard in the calculator to see the cost of the order.

Mixing it yourself: cement, sand and gravel

If you make your own concrete, mixes are written as parts of cement, sand and gravel by volume, such as 1:2:4. The dry materials take up more room than the wet concrete, about 1.54 times as much, so a cubic yard of 1:2:4 concrete needs about 5.9 bags of cement (a 94 lb bag is about 1 cubic foot), 0.44 cubic yards of sand and 0.88 cubic yards of gravel. These are estimates, because the real figures depend on the sand, the gravel and the water. Pick a mix in the calculator to see the amounts for your job.

Why add extra for waste?

Ground is rarely perfectly level, forms can bulge a little, and some concrete is spilled or left in the truck or the wheelbarrow. Running short in the middle of a pour is much worse than having a little left over, so most people add 5 to 10%. The calculator lets you set the extra and shows both the exact volume and the amount to order.

What does concrete weigh?

Normal ready-mixed concrete weighs about 150 pounds per cubic foot, or 2,400 kilograms per cubic meter. That is about 4,045 pounds, or 2 tons, per cubic yard. It matters for the ground, the forms and the vehicles that carry it.

How many concrete blocks for a wall?

Multiply the wall length by its height, take off doors and windows, and divide by the area one block covers including its mortar joint. A US standard block is 16 × 8 inches, so it covers 0.889 square feet and a wall 20 ft long and 4 ft high takes 90 blocks, or 95 with 5% extra for breakage and cuts. The Concrete Blocks tab does the sum for US, UK and Australian block sizes.

Calculators that go with this one

For the stone under a slab or a driveway, use the Gravel Calculator. To change inches to a fraction of a foot or to work out the extra for waste, see the Fraction Calculator and the Percentage Calculator.

View All Calculators

Frequently Asked Questions

How do I calculate cubic yards of concrete?

Multiply the length, width and thickness, all in feet, then divide by 27. For a slab 10 ft by 10 ft and 4 in thick, that is 10 × 10 × (4 ÷ 12) = 33.33 cubic feet, and 33.33 ÷ 27 = 1.23 cubic yards. Add 5 to 10% for waste.

How many bags of concrete do I need for a 10 x 10 slab?

For a slab 4 in thick, you need 33.33 cubic feet, which is 56 bags of 80 lb mix (an 80 lb bag makes 0.6 cubic feet). With 10% extra for waste it is 62 bags of 80 lb, or 82 bags of 60 lb.

How many 80 lb bags of concrete are in a yard?

A cubic yard is 27 cubic feet and an 80 lb bag makes 0.6 cubic feet, so it takes 45 bags. A 60 lb bag makes 0.45 cubic feet, so it takes 60 bags, and a 40 lb bag takes 90.

How much extra concrete should I order?

Most people add 5 to 10% for uneven ground, bulging forms and spillage. For a small job or a rough base, closer to 10% is safer. Running short in the middle of a pour is a bigger problem than having a little left over.

How much does a yard of concrete weigh?

Normal concrete weighs about 150 pounds per cubic foot, so a cubic yard is about 4,045 pounds, or 2 tons. A cubic meter weighs about 2,400 kg.

How thick should a concrete slab be?

Many patios, walkways and sidewalks are about 4 inches thick, and driveways and garage floors are often thicker. The right thickness depends on the load, the ground and your local building rules, so ask a builder.

How do I figure concrete for a footing?

Use the Slab or Footing tab and choose Footing. Enter the length, the width and the depth. A footing 100 ft long, 2 ft wide and 12 in deep is 200 cubic feet, or 7.41 cubic yards. Ask a builder for the sizes, because footings carry the weight of a building.

How much concrete do I need for a post hole or sonotube?

A round hole or tube is a cylinder, π × (diameter ÷ 2)² × depth. A hole 12 in across and 4 ft deep takes 3.14 cubic feet, or 0.116 cubic yards. Use the Column or Hole tab and enter how many holes you have.

How do I work out cubic meters of concrete?

Switch the units to meters and centimeters. Multiply the length and width in meters by the thickness in meters (cm ÷ 100). A slab 3 m by 3 m and 10 cm thick is 0.9 cubic meters, or 0.99 with 10% extra.

How much does concrete cost?

It depends on where you are, the mix and the delivery, so check with your supplier. Type the price per cubic yard (or per bag) in the calculator, and it multiplies it by your order to give the cost.

Should I use bags or ready-mix?

Bags suit small jobs, such as post holes or a small pad, because you can mix a little at a time. Larger pours are usually easier with ready-mix delivered by truck. Ask your supplier about delivery minimums.

How many yards of concrete are in a truck?

Ready-mix trucks carry up to about 10 cubic yards, and some smaller trucks carry less. Ask your supplier, because loads and delivery minimums vary.

How many concrete blocks do I need for a wall?

Divide the wall area, minus doors and windows, by the area of one block with its mortar joint. A 20 ft by 4 ft wall of US 16 × 8 in blocks takes 90 blocks, or 95 with 5% extra.

How much does a bag of concrete make?

An 80 lb bag makes about 0.6 cubic feet, a 60 lb bag 0.45 and a 40 lb bag 0.3. In cubic yards, an 80 lb bag makes about 0.022. Check the label of your bag, because yields vary a little.

How much cement, sand and gravel do I need?

For a 1:2:4 mix, one cubic yard of concrete needs about 5.9 bags of 94 lb cement, 0.44 cubic yards of sand and 0.88 cubic yards of gravel. These are estimates, because real mixes depend on the sand, the gravel and the water. Choose a mix in the calculator for your job.

Is this a substitute for a builder's or engineer's advice?

No. It is a planning estimate. For structural work such as foundations, footings and suspended slabs, ask a builder or an engineer for the sizes and the mix.