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Concrete Calculator

Use this concrete calculator to find the cubic yards, the bags of 80 lb and the weight of concrete for a slab or a footing, then go to the page for your job.

  • Instant answer as you type
  • Nothing you type is sent anywhere
  • Worked example with clear steps

Your measurements

ft
The limit of 10,000 is ours.
ft
in
4 is an example value, not a recommendation. The limit of 240 is ours.
%
Typical value, not a standard
Price per yard (optional)

The price is yours: we state none, and we store and show no prices.

$ per yd³

Result

Calculated live
Concrete to order 10% extra
1.36 yd³
Bags of 80 lb 61.11 before rounding up
62 bags
Volume as measured 1.23 yd³
33.33 ft³
Weight of the order 2.47 tons
4,938 lb

Based on NIST SP 811 NRMCA CIP 31 QUIKRETE data sheet Sakrete 80 lb page Full list of sources

Assumptions and constants

You can change

The limits on the other boxes, such as the largest size you can enter, are ours, not from a source.

Extra concrete to order Typical value

%
Same as the box in the form above

NRMCA says to order about 4% to 10% more concrete than the plan dimensions give. 10% is the top of that range.

Allowed range: 0 to 100 %.

Weight of one cubic yard of concrete Typical value

lb

The National Ready Mixed Concrete Association says one cubic yard of concrete weighs about 4000 lb (2 short tons). A bagged mix can weigh a little less: check your bag or supplier.

Allowed range: 3,000 to 5,000 lb per yd³. The limits are ours.

Fixed values (exact definitions and references)

These are exact definitions and cannot be edited.

Cubic feet in a cubic yard Reference [1]

27 ft³ per yd³

3 ft × 3 ft × 3 ft.

Inches in a foot Reference [1]

12 in per ft

The foot is 0.3048 m and the inch is 0.0254 m, both exact, so 12 inches make a foot.

Pounds in a US ton Reference [1]

2,000 lb per ton

The short ton of 2,000 lb, used by US suppliers.

How to use the concrete calculator

  1. Pick Slab or Footing, then enter the Length.
  2. Enter the Width, or the Footing width in inches.
  3. Enter the Thickness or depth, in inches.
  4. Check Extra to order.
  5. Read Concrete to order and Bags of 80 lb.
  6. Use Copy result or Print, and confirm the amount with your concrete supplier.

How much concrete for a slab?

A slab is its length times its width times its thickness. With the length and width in feet and the thickness in inches, cubic feet = length x width x thickness / 12, and cubic yards = cubic feet / 27. The same sum covers a sidewalk or a driveway, which are long, thin slabs. [1]

NRMCA advises topping up a calculation of the plan dimensions with about 4% to 10% more concrete, and says one cubic yard weighs about 4000 lb. [2] This calculator starts at 10%, the top of the range.

For bags, QUIKRETE's data sheet gives an 80 lb bag a yield of approximately 0.60 cubic feet. [3] Sakrete's page for its 80 lb mix says .6 cubic feet. [4] Read the yield on your own bag.

Worked example

A slab 10 ft long, 10 ft wide and 4 in thick: 10 x 10 x 4 / 12 = 33.33 cubic feet, and 33.33 / 27 = 1.23 cubic yards. With 10% extra, 1.23 x 1.1 = 1.36 cubic yards. At 0.6 cubic feet a bag, 36.67 / 0.6 = 61.1, which rounds up to 62 bags of 80 lb.

Slab: length 10 ft, width 10 ft A slab seen from above, a square. Its length, 10 ft, is marked under it and its width, 10 ft, along the right side. From above Length 10 ft Width 10 ft
Drawn to scale for a slab 10 ft long and 10 ft wide. The thickness, 4 in, goes into the page. The calculator turns the size into cubic yards, bags and weight.

How much concrete for a footing or foundation?

A footing is the same sum with a narrow width: length x width in inches / 12 x depth in inches / 12. A footing 40 ft long, 16 in wide and 8 in deep is 40 x 16 / 12 x 8 / 12 = 35.56 cubic feet, which is 1.32 cubic yards. Pick Footing above and enter the width in inches.

We found no source for the size of a footing. It depends on the load and the soil, so use the size on your plan or ask your building authority.

Ready mixed concrete

NRMCA says concrete is sold by the cubic yard. [2]

For a delivery, take the figure under Concrete to order to your supplier. For bags, use the bag count and check the yield printed on your bag.

Which concrete calculator for your job?

This page does a slab or a footing. For anything else, go to the page built for it:

How much does concrete cost?

We state no price. Ask local suppliers for a price per cubic yard, then enter it under Price per cubic yard, in the section Price per yard (optional) above, to see the total. The site does not store the prices you type.

Common mistakes and limits

  • Mixing units. Enter the length and width in feet, and the thickness and a footing's width in inches.
  • Ordering the measured amount. Check Extra to order against your supplier's advice.
  • What this tool does not cover: the mix, the strength, reinforcement, the base under the slab and frost.

Frequently asked questions

What is the difference between a slab and a footing?

For the arithmetic, nothing: both are a length times a width times a depth. A slab is wide and thin, so you enter its width in feet. A footing is a long narrow trench, so you enter its width in inches.

How thick should a concrete slab be?

We found no source we can cite for slab thickness, which depends on its use and your local rules. Ask your building authority, then enter the thickness under Thickness or depth. The 4 here is an example.

What concrete mix do I need for a slab?

We found no source we can cite for a mix, a ratio or a strength. Ask your concrete supplier or the designer of the slab, and read the bag if you mix from bags.

How much sand and gravel is in a yard of concrete?

We found no source for the proportions of sand, gravel and cement in a yard, so this calculator counts concrete, not its parts. Ready mixed concrete is ordered by the cubic yard.

How much does a yard of concrete weigh?

NRMCA says one cubic yard of concrete weighs about 4000 lb, so the slab in the example weighs about the same per yard. The weight of your order is under Weight of the order. [2]

Sources and references

  1. National Institute of Standards and Technology (NIST). NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically (SP 811, accessed November 2026). Used for: the inch and foot relationship, the 27 cubic feet in a cubic yard and the 2,000 pounds in a ton.
  2. National Ready Mixed Concrete Association (NRMCA). CIP 31, Ordering Ready Mixed Concrete (Concrete in Practice, PDF dated 2006, accessed November 2026). Used for: the weight of a cubic yard of concrete and the extra to order.
  3. The QUIKRETE Companies. Data Sheet, Concrete Mix, Product No. 1101-40, -50, -60, -80, -90 (revised October 2022, accessed November 2026). Used for: the yield of an 80 lb bag.
  4. Oldcastle APG (Sakrete). Sakrete High-Strength Concrete Mix 80 lb Gray (accessed November 2026). Used for: a second maker's yield for an 80 lb bag.

How we use sources: methodology.

Estimates only. Confirm quantities with your supplier. See the disclaimer. Found a wrong result? Report an error.