concrete.work
United States

Concrete Footing Calculator

Continuous footings under walls, square pad footings under posts, round piers with or without a bell, and monolithic slabs with thickened edges: pick the type and enter the sizes.

What are you pouring?
Continuous footing under a wall
Total length Width Depth

Tip: you can type feet and inches, like 10' 6".

Reinforcement for slabs (optional)
Gravel base under slabs (optional)

Gravel weight changes from quarry to quarry: ask your supplier for the compacted weight and we turn the volume into tons.

Use your own prices (optional)

You need

– cu yd

–

Poured, it weighs about – lb.

Premixed bags

Bag Bags To carry Est. cost

Mixing it yourself (1:2:3)

QUIKRETE Portland Cement data sheet: concrete mix 1 part cement, 2 parts All-Purpose Sand, 3 parts All-Purpose Gravel; 5 to 6 bags of 94 lb per yd³. A 94 lb bag is the customary 1 cu ft of cement.

Ready-mix truck

–

If a contractor pours it

How we price

Link to this calculation Download estimate (PDF)

Your materials at a glance

How to calculate concrete

  1. Add up the length. Measure every run of footing and add them together, in feet.
  2. Width and depth in inches. Divide by 12 to get feet.
  3. Multiply. Total length × width × depth gives cubic feet.
  4. Convert and add extra. Divide by 27 for yards and add 5–10%: trenches are rarely perfectly square.

Worked example: 9 pad footings for a deck, 24 × 24 × 12 in

  1. One footing: 2 × 2 × 1 = 4 cu ft. Nine footings: 36 cu ft.
  2. Plus 10% (dug holes are never square): 39.6 cu ft = 1.47 cubic yards.
  3. In 80 lb bags: 66 bags in total (8 if you buy for each footing separately).

Concrete per 10 feet of footing

Width × depth Cubic feet Cubic yards 80 lb bags
12 × 6 in 5.00 0.19 9
16 × 8 in 8.89 0.33 15
20 × 8 in 11.11 0.41 19
20 × 10 in 13.89 0.51 24
24 × 12 in 20.00 0.74 34

Per 10 linear feet, no waste included.

Concrete per square pad footing

Footing Depth Cubic feet 80 lb bags 60 lb bags
16 × 16 in 8 in 1.19 2 3
16 × 16 in 12 in 1.78 3 4
18 × 18 in 8 in 1.50 3 4
18 × 18 in 12 in 2.25 4 5
20 × 20 in 8 in 1.85 4 5
20 × 20 in 12 in 2.78 5 7
24 × 24 in 8 in 2.67 5 6
24 × 24 in 12 in 4.00 7 9
30 × 30 in 8 in 4.17 7 10
30 × 30 in 12 in 6.25 11 14
36 × 36 in 8 in 6.00 10 14
36 × 36 in 12 in 9.00 15 20

One footing, no waste included.

Concrete formulas by shape

All measurements in feet; divide inches by 12 first. Results are in cubic feet.

Continuous footing
total length × width × depth
Pad footing
length × width × depth × number of footings
Monolithic slab
length × width × thickness + perimeter band × (edge depth − thickness), where perimeter band = length × width − (length − 2 × edge width) × (width − 2 × edge width)
Column / pier
π × (diameter ÷ 2)² × height
Bell footing
π × r² × pier height + π × bell height ÷ 3 × (R² + R × r + r²), with r = pier radius and R = bell radius

Cubic yards = cubic feet ÷ 27.

Frequently asked questions

How big should a footing be?

It depends on the load, the soil and the frost depth where you live, so the size comes from your plans or building department. The calculator only needs the dimensions.

How do I calculate concrete for a pier footing?

Use π × radius² × depth, in feet, times the number of piers. Choose "Column / pier" in the calculator.

Should I order extra for a footing?

Yes. Dug trenches are irregular and soak up more concrete than the drawing suggests; 10% extra is a safe start.

About the prices

Costs are estimated ranges with source and date, never a quote. Enter your local prices under "Use your own prices", or read how we estimate prices.