Primary material
62 bags
80 lb concrete mix
Use the calculated bag count as your buying starting point, then verify yield and pallet limits with the store.
Concrete footing calculator
Concrete footing calculator for strip and pad footings.
Enter footing length, width, depth, and waste allowance to estimate cubic yards, bag count, and rough material cost.
20 ft x 12 in x 8 in
0.54 yd³
25 bags at 80 lb
Formula
L x W x D
Width/depth converted to feet
Best for
Footings
Walls, piers, pads, forms
Quick reference
Concrete for common strip footing sizes
Cubic yards and bags per run of footing, including the default 10% waste.
| Footing size | Yards per 20 ft | 80 lb bags per 20 ft | Yards per 50 ft |
|---|---|---|---|
| 12 in wide x 6 in deep | 0.41 yd³ | 19 | 1.02 yd³ |
| 16 in wide x 8 in deep | 0.72 yd³ | 33 | 1.81 yd³ |
| 20 in wide x 10 in deep | 1.13 yd³ | 51 | 2.83 yd³ |
| 24 in wide x 12 in deep | 1.63 yd³ | 74 | 4.07 yd³ |
Footing width and depth are set by your local code and the wall they carry — confirm before you dig.
Quick footing answers
Common footing sizes
20 ft strip footing
20 ft x 12 in x 8 in
0.54 yd³
25 bags at 80 lb with default 10% waste
40 ft wall footing
40 ft x 16 in x 8 in
1.45 yd³
66 bags at 80 lb with default 10% waste
Pad footing
4 ft x 24 in x 12 in
0.33 yd³
15 bags at 80 lb with default 10% waste
Structural note
This page estimates concrete quantity. Footing design, reinforcement, frost depth, and soil bearing are structural questions and should be verified before pouring.
Shopping list
Ready to price and order
Use the calculated quantities as a starting cart, then compare store availability, delivery fees, pallet limits, and local ready-mix minimums before buying.
Large pours
Ready-mix quote check
For high bag counts, compare the bagged route against local ready-mix minimums, delivery, access, and unload time.
Optional base
Gravel base
Base depth is project-specific. Estimate it separately before adding bags or bulk gravel to the order.
Optional forms
Forms and stakes
Plan lumber, stakes, screws, release, and bracing around the perimeter and any step-downs or curves.
Store buttons open retailer search results for now. Confirm exact product yield, pickup, delivery, and pallet rules before ordering.
Formula shown
How the footing calculation works
1. Convert width and depth to feet
width ft = width in / 12; depth ft = depth in / 12
2. Calculate footing volume
cubic feet = length ft x width ft x depth ft
3. Add waste and estimate bags
bags = ceil(cubic feet x (1 + waste) / bag yield)
Footing edge cases
Step footings, thickened pads, keyways, pier pads, and over-excavation should be estimated separately and added to the continuous footing volume.
Sources
- Quikrete product yields — bagged concrete mix yield references
- Sakrete bagged concrete references — common bag sizes and concrete mix guidance
- ConcreteNetwork concrete price guide — ready-mix and installed concrete cost context
Sources checked
Checked against
Bag yields checked against Quikrete and Sakrete product specs; price ranges against published concrete cost guides.
How we check our numbersLast updated: June 20, 2026
Estimate only.
This calculator is not a quote. Verify product yield, price, delivery minimums, and local conditions with your supplier or contractor before buying materials.
FAQ
Concrete footing questions
Answers for footing volume, bags vs ready-mix, footing vs slab differences, and structural limitations.
How do I calculate concrete for a footing? + -
Multiply footing length in feet by width in feet by depth in feet. This calculator lets you enter length in feet and width/depth in inches, then converts the units and adds waste.
How much concrete is needed for a 20 ft footing? + -
For a 20 ft long footing that is 12 inches wide and 8 inches deep, the calculator estimates about 0.54 cubic yards with the default 10% waste allowance, or about 25 bags of 80 lb concrete mix. The waste percentage is editable.
What is the difference between a footing and a slab? + -
A slab is usually a broad flat surface. A footing is usually a strip or pad below a wall, pier, or foundation element, so its width and depth drive the volume differently.
Should footings be ordered as ready-mix? + -
Small pad footings may be practical with bags. Long continuous footings can require many bags, so ready-mix may be easier and more consistent if delivery is available.
Is this footing estimate a structural design? + -
No. It estimates concrete quantity and rough material cost only. Footing size, reinforcement, frost depth, soil bearing, and local code should be verified with a qualified professional.