Concrete & Masonry
Concrete Footing Calculator
Choose strip or pad footings, then enter the size from your plans. The calculator turns it into cubic yards and 80 lb bags with waste added.
Worked example
- 80 ft x (16/12) ft x (8/12) ft = 71.11 cu ft.
- Plus 10% waste = 78.22 cu ft = 2.90 cu yd.
Common sizes at a glance
| Size | Concrete | 80 lb bags |
|---|---|---|
| 16 x 8 in strip, 50 ft | 1.81 cu yd | 82 |
| 20 x 10 in strip, 100 ft | 5.66 cu yd | 255 |
| 24 x 12 in strip, 140 ft | 11.41 cu yd | 514 |
| Nine 24 x 24 x 12 in pads | 1.47 cu yd | 66 |
Strip footings and pad footings
A strip footing runs continuously under a wall, so you enter the total length around the building plus one width and depth. A pad footing is a square or rectangle under a post or pier, so you enter the size of one pad and how many there are.
The worked example is an 80 ft strip, 16 in wide and 8 in deep. With 10% waste that is 2.90 cu yd, or 131 bags of 80 lb.
Size comes from the plans, not from us
Footing width and depth depend on the soil, the load and the frost depth in your area. This calculator does not size footings. Take the numbers from your approved plans; the local building code and a licensed professional have the final word.
Once those sizes are set, counting the concrete is simple, and that is the part this page handles.
Measuring the total run
For a rectangle, add up all four sides measured along the center of the footing. Measuring the outside edge counts the corners twice and overstates the total a little; measuring the inside edge understates it.
Add interior bearing lines and any jogs in the wall. Missing a 12 ft run of a strip 20 in wide and 16 in deep leaves you almost a full yard short.
Trenches are bigger than drawn
Footings poured straight into a dug trench take the shape of the trench, and trenches tend to be wider than the plan. If the excavator bucket is wider than the footing, measure the real trench width.
Soft spots that are dug out and filled with concrete also add volume. A 10% allowance is a starting point; raise it for earth-formed trenches.
After the footing
Most footings carry a foundation wall or piers next. The concrete block calculator handles a block foundation, and the rebar calculator counts bars for a slab grid.
Questions
How much concrete for nine 24 x 24 x 12 in pads?
About 1.47 cu yd with waste, or 66 bags of 80 lb.
Should I use bags or ready-mix for footings?
Small pad footings are fine with bags. A full strip footing around a house usually means a truck order.
Does the result include steel?
No. Reinforcement in footings is set by the plans and code, and it takes up very little volume.
How this works: formulas and typical values are listed on our method page; every data source and its license is on sources.
Last reviewed November 2026.