PourGaugeHow much concrete you actually need, and what to mix into it.

Block wall materials for 60 ft at 2 courses, rebar every 24″

Blocks needed
958×8×16 blocks
60 ft long × 2 courses (1.33 ft) — 80 ft² of wall, 5% breakage included
Elevation60 ft2 courses · 1.33 ft95 blocks · 3 bags mortar · 31 vertical bars
Blocks (with 5% breakage)95blocks
Blocks (exact)1.125 per ft² including joints90blocks
Wall area60 ft × 1.33 ft80ft²
Wall height2 courses at 8″1.33ft
Mortar (Type S, 70 lb)3 bags per 100 blocks at ⅜″ joints3bags
Masonry sandif mixing from bagged cement and lime instead0.4yd³
Vertical rebar (#4 @ 24″)88 linear ft including 18″ into the footing31bars
Grout for filled cells27 × 80 lb bags — only the cells with steel in them16.1ft³
Footing16″ × 8″ × 60 ft — twice the wall thickness1.98yd³
Engineeringunder 4 ft in most jurisdictionsUsually 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 — 31 cells here, 16.1 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

60 ft × 2 courses is 1.33 ft high and 80 ft² of wall — 95 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

3 bags of Type S at ⅜″ joints, or 0.4 yd³ of masonry sand if you are mixing from cement and lime instead.

Steel and grout

31 vertical bars, 88 linear ft including 18″ of anchorage into the footing, and 16.1 ft³ of grout — 27 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

1.98 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

Read more