Concrete Footing Calculator

Add your strip, pad and round footings to get the cubic yards of concrete and the number of 40, 60 and 80 lb bags.

How to calculate concrete for a footing

Concrete is sold by volume, and in the United States the unit is the cubic yard, which is 27 cubic feet. Find the volume of each footing in cubic feet, multiply by how many you have and divide the total by 27. Measure the width and the thickness in inches if you like and the calculator turns them into feet.

Footing	Formula, in feet	Example
Strip (continuous)	length × width × thickness	60 × 1.3333 × 0.6667 = 53.33 ft³ = 1.98 yd³
Pad (square or rectangle)	length × width × thickness × how many	2 × 2 × 1 × 4 = 16 ft³ = 0.59 yd³
Round	π × (diameter ÷ 2)² × thickness × how many	π × 0.75² × 4 = 7.07 ft³ = 0.26 yd³

A footing job often mixes types, such as a strip footing under a wall and a few pad footings under posts. Click “Add another footing” to add each one and the calculator adds them for you. Type a measurement like 10'6" or 10 ft 6 in in any box if that is how your plans read.

Example: 60 ft of strip footing, 16 inches wide and 8 inches thick

A strip footing is 60 ft long, 16 inches wide and 8 inches thick. You decide to add 10% waste. These are the figures the calculator gives when you type them in.

Step	Operation	Result
Width and thickness in feet	16 ÷ 12 and 8 ÷ 12	1.3333 ft and 0.6667 ft
Volume	60 × 1.3333 × 0.6667	53.33 ft³
With 10% waste	53.33 × 1.10	58.67 ft³
Cubic yards	58.67 ÷ 27	2.1728 yd³
80 lb bags	58.67 ÷ 0.60 = 97.78, rounded up	98 bags
60 lb bags	58.67 ÷ 0.45 = 130.37, rounded up	131 bags
40 lb bags	58.67 ÷ 0.30 = 195.56, rounded up	196 bags

The bag yields are the manufacturer’s figures for QUIKRETE Concrete Mix (data sheet revised October 2022, checked October 2026), which lists footings among its uses and says it is designed for pours 2 inches thick or more. A cubic yard is 45 bags of 80 lb, 60 of 60 lb or 90 of 40 lb. The data sheet gives approximate yields, so check the figure printed on your bag.

Cubic yards for every 100 feet of strip footing

A quick table when you only know the run. It is plain geometry, 100 × width × thickness ÷ 27, and it does not say which size you should build.

Thickness	12 in wide	16 in wide	20 in wide	24 in wide
6 in	1.85	2.47	3.09	3.70
8 in	2.47	3.29	4.12	4.94
10 in	3.09	4.12	5.14	6.17
12 in	3.70	4.94	6.17	7.41

Who decides the size of a footing

The width, thickness and depth of a footing depend on the load it carries, on the soil and on the local code. Your building department or the plans for the job give you the numbers. As an example only, the city of Bullhead City, Arizona summarizes the 2018 International Residential Code (Table R403.1(1)) for a one- or two-story slab-on-grade house, with a 20 psf roof load and 1,500 psf soil, as at least 12 inches wide and 6 inches thick, and at least 12 inches below the undisturbed ground surface. That is one city’s summary for one set of conditions, not the code itself, so do not use it for your own project without checking.

Pad and round footings. Use the “Pad” type for a square or rectangular footing under one column and “Round” for one poured in a hole or a form. For round tubes, see the Sonotube calculator.
Slabs. A slab is measured the same way, with its own thickness. The concrete calculator has slab, wall, column and step tabs.
Gravel under the footing. If you add a base, calculate it with the gravel calculator. Its volume is separate from the concrete.
Posts. A single fence or deck post in a hole has its own tool, the post hole concrete calculator, which subtracts the volume of the post.

Bags or a ready-mix truck?

Bags make sense for a few small footings. Compare the bag count with a ready-mix quote. The cubic yards in the big figure are the number to give the supplier. Cemex suggests adding 10 to 15% to a ready-mix order and states a minimum order of 1 cubic yard per delivery. Sakrete suggests adding 10% to every estimate. Other suppliers set their own minimums, so ask before you plan a small pour. This page does not show prices, because they change by region and supplier.

If you mix the bags yourself, QUIKRETE’s data sheet advises at least 1 cubic foot of mixer capacity for each 80 lb bag. For load-bearing work, it says to follow your local building code for the footing specifications.

Frequently asked questions

How do I calculate how much concrete I need for a footing?

Multiply the length, the width and the thickness, all in feet, and divide by 27 to get cubic yards. A strip footing 60 ft long, 16 inches wide and 8 inches thick is 60 × 1.3333 × 0.6667 = 53.33 cubic feet, which is 1.98 cubic yards. For a round footing use π × (diameter ÷ 2)² × thickness instead.

What is a concrete footing?

It is the concrete that sits on the ground under a wall, a column, a post or a deck and carries their load. A strip footing runs along a wall, a pad footing sits under a single column or post, and a round footing is poured into a hole or a tube. The calculator measures the volume of each type.

How many bags of concrete is 1 cubic yard?

With the QUIKRETE Concrete Mix yields it is 45 bags of 80 lb, 60 bags of 60 lb or 90 bags of 40 lb, because a cubic yard is 27 cubic feet and the bags yield 0.60, 0.45 and 0.30 cubic feet. Other brands can differ, so check the yield on your bag.

How much concrete do I need to pour 1,500 square feet?

It depends on the thickness. At 4 inches, 1,500 square feet is 500 cubic feet, which is 18.52 cubic yards. At 6 inches it is 750 cubic feet, which is 27.78 cubic yards. Use the same math for a footing, but with its width and thickness.

How do I calculate how much concrete to order?

Work out the cubic yards of every footing and add them. Then add a margin. Cemex suggests 10 to 15% on a ready-mix order for spillage, uneven subgrades and other variables, and Sakrete suggests 10% on every estimate. Type your percentage in the waste box. Ready-mix suppliers also set minimum loads, and Cemex states 1 cubic yard per delivery, so ask yours.

How wide and how deep should a footing be?

Your local building department decides, because it depends on the loads, the soil and the climate. The calculator does not suggest a size. Type the dimensions on your plans or the ones your inspector gave you. Section “Who decides the size of a footing” below shows one city’s summary of the International Residential Code for a simple case.

Is it cheaper to pour a footing with bags or to order a truck?

It depends on local prices, which change by region and supplier, so this calculator does not show them. Take the number of bags and the cubic yards from the result and compare them with a delivery quote.