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Footing run × width × depth in feet ÷ 27 = cubic yards, plus 8% over-pour. A 30 × 40 ft house has 140 ft of footing: at 16 × 8 in that is 4.61 cu yd, about 5 yards. An 8 × 24 in stem wall adds 6.91 cu yd. One yard is 45 bags of 80 lb mix.
To work out the concrete for a footing, multiply the footing run by its width and depth in feet, divide by 27 for cubic yards and add about 8% for over-pour. For a rectangular building the run is the perimeter, 2 × (length + width): a 30 × 40 ft house has 140 ft of footing, and at 16 in wide and 8 in deep that is 124.4 cu ft, 4.61 cu yd, so order about 5 yards. An 8 in thick, 24 in tall stem wall on the same footing adds 186.7 cu ft (6.91 cu yd), 12.4 yards in all with the over-pour, and square pier pads add count × side × side × depth. One cubic yard is 45 bags of 80 lb mix (0.60 cu ft each), 60 bags of 60 lb or 90 of 40 lb; ready-mix runs about $160–$210 a yard plus a short-load fee under 4 yards. The 2021 IRC (R403.1.1) sets the minimum footing at 12 in wide and 6 in thick, with the bottom below the frost line and at least 12 in below undisturbed ground; the actual size comes from the code tables or the engineer for your soil and house.
Short answer: footing run × width × depth (ft) ÷ 27 = cubic yards; add 8% for over-pour. A 30 × 40 ft house (140 ft of footing) at 16 × 8 in is 124.4 cu ft, 4.61 cu yd, about 5 yards; an 8 × 24 in stem wall adds 6.91 cu yd. One cubic yard is 45 bags of 80 lb mix.
| Building | Run | Footing only | 80 lb bags | Footing + 24 in wall |
|---|---|---|---|---|
| 24 × 24 ft garage | 96 ft | 3.41 cu yd | 154 | 8.53 cu yd |
| 24 × 32 ft | 112 ft | 3.98 cu yd | 180 | 9.96 cu yd |
| 30 × 40 ft house | 140 ft | 4.98 cu yd | 224 | 12.44 cu yd |
| 40 × 60 ft | 200 ft | 7.11 cu yd | 320 | 17.78 cu yd |
2021 IRC R403.1.1: at least 12 in wide and 6 in thick. R403.1.4: bottom at least 12 in below undisturbed ground and below the frost line. Wider footings for more stories, brick veneer and weaker soil; the code tables or the engineer set the size.
Over about a yard, ready-mix at $160–$210 a yard is usually the better buy even with a short-load fee under 4 yards. Pour a continuous footing in one go: a cold joint mid-wall is a weak spot.
Multiply the footing's length by its width and depth in feet, divide by 27 for cubic yards and add about 8% for over-pour. A 30 × 40 ft house has 140 ft of footing; at 16 in wide and 8 in deep that is 124.4 cu ft, 4.61 cu yd, so order about 5 yards.
Add the wall to the footing: run × wall thickness × wall height. On the same 30 × 40 ft house an 8 in thick, 24 in tall stem wall adds 186.7 cu ft (6.91 cu yd), so footing and wall together take 11.52 cu yd, about 12.4 yards to order with 8% extra.
The 2021 IRC (R403.1.1) sets a minimum of 12 in wide and 6 in thick, and the bottom must sit below the local frost line and at least 12 in below undisturbed ground (R403.1.4). Wider footings are required for heavier houses and weaker soils; 16 × 8 in is a common size for a one or two story house. Your building department sets the exact size.
Cubic yards × 27 ÷ the bag's yield: 0.60 cu ft for an 80 lb bag, 0.45 for 60 lb and 0.30 for 40 lb, so one cubic yard is 45 bags of 80 lb mix. A 24 × 24 ft garage footing at 16 × 8 in is about 3.41 cu yd to order, or 154 bags of 80 lb. Above about a yard, ready-mix is usually easier and similar in cost.
Ready-mix runs about $160–$210 a yard on this site's concrete calculator, plus a short-load fee of roughly $180–$300 under 4 yards. The 30 × 40 ft footing above (about 5 yards) is about $796–$1,045 in concrete, before forms, rebar, excavation and labor.
Two continuous #4 bars is the common minimum where the code or the plans call for footing steel. Linear feet = footing run × number of bars, plus about 10% for laps and corner bends: 140 ft × 2 × 1.1 = 308 ft, or 16 twenty-foot sticks. Seismic and engineered foundations can require more; follow the plans.
Side × side × depth in feet per pad, times the number of pads, ÷ 27. Twelve 24 × 24 in pads 12 in deep are 12 × 2 × 2 × 1 = 48 cu ft, 1.78 cu yd, or about 1.9 yards with 8% extra. Round pier holes and sonotubes use π × radius² × depth instead.
No. The footing is the wide concrete pad at the bottom that spreads the load into the soil; the foundation wall (stem wall) sits on it and carries the house up above grade. A monolithic slab pours both at once with a thickened edge; this calculator covers footing and wall poured separately.
Pouring the floor slab too? The concrete slab calculator gives the slab in yards and bags.
Block foundation instead of a poured wall? The concrete block calculator counts the blocks and mortar.
Need the whole roof at once? The free roofing calculator works out roof area, squares, shingle bundles, underlayment, drip edge, ridge cap and installed cost from one set of measurements.