Concrete for a 20″ × 16″ footing, 10 ft long
| Ready-mix | 0.91yd³ |
|---|---|
| 80 lb bags0.6 ft³ per bag | 41bags |
| 60 lb bags0.45 ft³ per bag | 55bags |
| Volume (exact)before waste | 22.22ft³ |
| Volume (order this)+10% | 24.44ft³ |
| Rebar (3 × #4 continuous)no laps — one stick covers it | 30linear ft |
| 20 ft rebar sticks | 2sticks |
| Form boardsboth sides, if the trench will not stand | 27ft² |
| Thickness check16″ is at least 6″ and at least a third of the width | OK |
Notes
- 16″ thick on a 20″ wide footing satisfies the usual rule: at least 6″, and at least as thick as the footing projects past the wall on each side. Below that the footing bends before it spreads the load.
- Rebar is what makes it a footing rather than a strip of concrete. 3 continuous #4 bars are the IRC minimum for a reinforced footing, laps included here at 20″ — 30 linear ft in total, or 2 sticks of 20 ft.
- Under 1 yd³ bagged mix is affordable, but a footing still has to go in continuously. Mix ahead, have help, and do not start until everything is in the trench.
- Bottom of the footing goes below the frost line and onto undisturbed soil. Pouring onto backfill or into a trench with loose spoil in the bottom means the footing settles no matter how much steel is in it.
Volume
20″ × 16″ × 10 ft is 24.44 ft³ once 10% is added for an uneven trench bottom — 0.91 cubic yards, or 41 bags of 80 lb mix if you are going that route.
Rebar, laps included
3 continuous #4 bars are the IRC minimum for a reinforced footing, and footings 20″ and wider normally take three. Over 10 ft that is 30 linear ft with no laps at 20″ each — 2 sticks of 20 ft rebar.
The laps are the part people forget when they order steel, and running short mid-pour is not a recoverable mistake.
Thickness
The rule is at least 6″, and at least as thick as the footing projects past the wall on each side. Below that the footing bends before it spreads load, and the reinforcement is being asked to do a job the geometry will not let it do.
Forms
27 ft² of board if the trench will not stand on its own. Firm undisturbed soil holds a clean trench and you can pour straight against it; sand, fill or anything that has been rained on will not.
Where it sits matters more than what is in it
Below the frost line, on undisturbed soil. Pouring onto backfill or into a trench with loose spoil in the bottom means the footing settles no matter how much steel went in.
Nearby sizes
- Concrete for a 18″ × 16″ footing, 10 ft long
- Concrete for a 24″ × 16″ footing, 10 ft long
- Concrete for a 16″ × 16″ footing, 10 ft long
- Concrete for a 30″ × 16″ footing, 10 ft long
- Concrete for a 20″ × 12″ footing, 10 ft long
- Concrete for a 20″ × 20″ footing, 10 ft long
- Concrete for a 20″ × 10″ footing, 10 ft long
- Concrete for a 20″ × 24″ footing, 10 ft long
Read more
- How Deep Should Footings Be? Frost Depth Decides, Not LoadDepth and diameter answer two completely different questions. Diameter is about carrying weight. Depth is about a force that has nothing to do with weight at all.
- Footing Size for a Deck Post: Working Backwards from the SoilAlmost every deck footing question gets answered with "twelve inches" or "sixteen inches". Both are sometimes right and neither is an answer, because the number is decided by the ground, not by the post.
- Bags or a Truck — The Crossover Is About One Cubic YardThe arithmetic is not really about price. It is about how long a slab can sit half-poured before the joint between the halves becomes permanent.
- Rebar in a Slab — Spacing, Cover, and Why Position Matters MoreRebar laid on the ground and left there does nothing. It has to be held up into the concrete, and that is the step that gets skipped.