Block wall materials for 20 ft at 2 courses, rebar every 24″
| Blocks (with 5% breakage) | 32blocks |
|---|---|
| Blocks (exact)1.125 per ft² including joints | 30blocks |
| Wall area20 ft × 1.33 ft | 27ft² |
| Wall height2 courses at 8″ | 1.33ft |
| Mortar (Type S, 70 lb)3 bags per 100 blocks at ⅜″ joints | 1bags |
| Masonry sandif mixing from bagged cement and lime instead | 0.13yd³ |
| Vertical rebar (#4 @ 24″)31 linear ft including 18″ into the footing | 11bars |
| Grout for filled cells10 × 80 lb bags — only the cells with steel in them | 5.7ft³ |
| Footing16″ × 8″ × 20 ft — twice the wall thickness | 0.66yd³ |
| Engineeringunder 4 ft in most jurisdictions | Usually not |
Notes
- 1.125 blocks per square foot is the number, and it already includes the ⅜″ mortar joints. A "8×8×16" block is 7⅝ × 7⅝ × 15⅝ actual — the missing ⅜″ is the joint, which is why nominal dimensions divide so cleanly into wall areas.
- Grout goes only in the cells that have steel in them — 11 cells here, 5.7 ft³. Solid-grouting the whole wall is a different job with several times the material and a footing sized for several times the load.
- Under 4 ft, a straightforward garden or stem wall is normally within what a homeowner can build to prescriptive rules. Check locally, and check specifically whether it retains soil — that changes the answer everywhere.
- The footing decides whether the wall lasts. 16″ × 8″ is the usual rule of twice the wall thickness, below the frost line, on undisturbed soil. Block laid on a footing that heaves cracks along the mortar joints, and there is no repair short of rebuilding.
- Drainage behind any wall holding back soil is not optional: gravel backfill, a perforated pipe at the base and weep holes. Water pressure behind a wall is a larger force than the soil itself, and it is what actually pushes walls over.
Blocks
20 ft × 2 courses is 1.33 ft high and 27 ft² of wall — 32 blocks with 5% for breakage and cuts.
The number to remember is 1.125 blocks per square foot, and it already includes the ⅜″ mortar joints. A block sold as 8×8×16 actually measures 7⅝ × 7⅝ × 15⅝; the missing ⅜″ is the joint, which is why nominal sizes divide so neatly into wall areas.
Mortar
1 bags of Type S at ⅜″ joints, or 0.13 yd³ of masonry sand if you are mixing from cement and lime instead.
Steel and grout
11 vertical bars, 31 linear ft including 18″ of anchorage into the footing, and 5.7 ft³ of grout — 10 bags.
Grout goes only in the cells that have steel in them. Solid-grouting the whole wall is a different job with several times the material and a footing sized for several times the load.
The footing decides whether it lasts
0.66 yd³ at 16″ × 8″, below the frost line, on undisturbed soil. Block laid on a footing that heaves cracks along the mortar joints, and there is no repair short of taking it down.
Before you start
Anything over 4 ft, and anything at all that retains soil, needs an engineered design and a permit almost everywhere. Soil pushes sideways with a force that grows with the square of the height, and walls sized by rule of thumb fail by tipping over rather than by crushing.
Drainage behind a retaining wall is not optional either: gravel backfill, perforated pipe at the base, weep holes. Water pressure behind a wall is a bigger force than the soil, and it is what actually pushes walls over.
Nearby sizes
- Block wall materials for 16 ft at 2 courses, rebar every 24″
- Block wall materials for 24 ft at 2 courses, rebar every 24″
- Block wall materials for 12 ft at 2 courses, rebar every 24″
- Block wall materials for 28 ft at 2 courses, rebar every 24″
- Block wall materials for 20 ft at 3 courses, rebar every 24″
- Block wall materials for 20 ft at 4 courses, rebar every 24″
Read more
- How Many Blocks for a Wall: The 1.125 Rule and What It Leaves OutA standard block covers exactly 0.889 square feet of wall including its mortar joint, which is why one number does all the work — and why the block count is the least of your problems.
- 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.
- Concrete Slab Cost by State — 400 ft², All 51The figures price a 4-inch slab on grade. A driveway wants six inches and rebar, and that is not a small adjustment.