Core Fill Grout Calculator
A core fill grout calculator divides wall area by 107 sq ft per cubic yard for fully grouted 8 in block: a 20 × 8 ft wall needs about 1.50 yd³ of grout.
How much core fill grout do I need?
A core fill grout calculator works from the face of the wall. Multiply wall length by height to get square feet, then divide by 107, the square feet of standard 8-inch concrete block that one cubic yard of grout fills when every cell is grouted. A 20 ft long, 8 ft tall wall is 160 sq ft, so it needs 160 ÷ 107 = 1.50 cubic yards. At $160 per yard, that is $239.25 of grout.
Enter the wall length and height in feet and your price per cubic yard. The result is not rounded. Round up to the nearest quarter or half yard your supplier sells.
The formula in plain words
- Wall area = length × height
- Cubic yards = wall area ÷ 107
- Cost = cubic yards × price per yard
The 107 figure means each square foot of fully grouted 8-inch wall takes about 0.25 cubic feet of grout. That is the hollow space left inside the block after the webs and face shells.
Worked examples
Both use $160 per cubic yard.
- Garden retaining wall, 20 × 8 ft, every cell grouted**
- Area: 20 × 8 = 160 sq ft (about 180 blocks)
- Grout: 160 ÷ 107 = 1.50 yd³
- Cost: 1.4953 × $160 = $239.25
- Order: 1.75 yd³ to cover losses
- Foundation stem wall, 40 × 6 ft, every cell grouted**
- Area: 40 × 6 = 240 sq ft
- Grout: 240 ÷ 107 = 2.24 yd³
- Cost: $358.88
- If the drawings only call for cells at 48 in on center, the fill drops to about 2.24 ÷ 6 = 0.37 yd³, plus any bond beams.
Grout for common wall sizes
Fully grouted 8-inch CMU at 107 sq ft per cubic yard.
| Wall (L × H) | Face area | Grout | At $160/yd³ |
|---|---|---|---|
| 10 × 4 ft | 40 sq ft | 0.37 yd³ | $59.81 |
| 20 × 8 ft | 160 sq ft | 1.50 yd³ | $239.25 |
| 30 × 8 ft | 240 sq ft | 2.24 yd³ | $358.88 |
| 50 × 10 ft | 500 sq ft | 4.67 yd³ | $747.66 |
| 100 × 8 ft | 800 sq ft | 7.48 yd³ | $1,196.26 |
Partial grouting by cell spacing
Grout per 100 sq ft of 8-inch wall, before bond beams and waste.
| Grouted cells | Share of cells | Grout per 100 sq ft |
|---|---|---|
| Every cell (solid) | 1 of 1 | 0.935 yd³ |
| 16 in on center | 1 of 2 | 0.467 yd³ |
| 24 in on center | 1 of 3 | 0.312 yd³ |
| 32 in on center | 1 of 4 | 0.234 yd³ |
| 48 in on center | 1 of 6 | 0.156 yd³ |
Bond beams are horizontal courses of U-shaped block, filled solid along the full wall length. Add them as a separate strip: wall length × 0.67 ft course height ÷ 107 × 1 for each grouted course.
Fine or coarse grout
Masonry grout comes as fine grout (sand only) or coarse grout (sand plus pea gravel). Small cores and narrow spaces usually take fine grout, but the spec or engineer decides.
How to measure
Measure the wall face in feet, from the top of the footing to the top course. Include pilasters and corners as part of the length. Openings for doors or windows can be subtracted, but leave lintels and jambs in, since those cells are usually grouted solid. Use the same face area you would use for a block count.
Common mistakes
- Applying the 8-inch rate to 12-inch block. Larger block has bigger cores and needs more grout per square foot. Use the manufacturer’s core volume data.
- Forgetting bond beams. A wall grouted at 48 inches can have as much grout in its bond beams as in its vertical cells.
- Using mortar as grout. Mortar is too stiff to flow to the bottom of a cell and leaves voids.
- Ordering the bare number. Grout seeps into adjacent cores and spills at the top, and a short load is costly with a pump on site.
Related calculators
Count the block for the same wall with the concrete block calculator, the bagged mix for the joints with the mortar calculator, and steel with the rebar calculator. Grouted block walls are structural, so have a licensed engineer or masonry contractor confirm cell spacing, rebar, and lift heights for your project.
Frequently asked questions
How much grout do I need to fill all the cells of a block wall?
This calculator uses 107 sq ft of 8-inch CMU wall per cubic yard of grout when every cell is filled, which is about 0.25 cu ft of grout per sq ft of wall. A 20 × 8 ft wall (160 sq ft) needs 160 ÷ 107 = 1.50 cubic yards. Add 5 to 10% for spillage and grout lost into ungrouted cores.
Do I need to grout every cell, or just some?
It depends on the design. Many reinforced walls grout only the cells holding vertical rebar, for example every 32 or 48 inches on center, plus bond beams. Retaining walls and some foundation walls are fully grouted. Follow the engineer's drawings or local code; this calculator assumes every cell is filled.
How do I estimate partial grouting?
Divide the full-grout result by the share of cells you will fill. Cells in standard 16-inch block sit 8 inches apart, so grouting at 48 inches on center fills 1 cell in 6. For a 240 sq ft wall, full grout is 2.24 yd³, so 48-inch spacing is about 2.24 ÷ 6 = 0.37 yd³, plus any bond beam courses.
Why is core fill grout different from mortar?
Mortar is a stiff paste that beds the blocks and fills the 3/8-inch joints. Core fill grout is a fluid mix poured or pumped into the hollow cores to bond the blocks and rebar into one solid wall. Grout is usually ordered by the cubic yard from ready-mix or a grout pump, while mortar comes in bags.
Does core fill grout need consolidation?
Yes. Grout is rodded or vibrated after placement to fill voids around the rebar and in the bottom of each cell. Tall walls are usually grouted in lifts, and the allowable lift height depends on the grout mix, cleanouts, and the project spec. Check with the engineer before pouring a full-height wall in one go.
Estimates only. Verify quantities with your supplier before purchasing.