Choose the block width and how often cells are grouted, and enter the wall size. The calculator reads the grout volume from the NCMA estimating table and gives cubic yards for a grout truck or pump, and bags for hand filling.
Block fill / core grout calculator
How it works
NCMA TEK 4-2A Table 3 lists the grout needed per 100 sq ft of wall for two-core hollow units, by wall width and grout spacing. The values include 3% waste.
- Grout = wall area ÷ 100 × table value (cu ft)
- Bags by volume = grout ÷ yield per bag (NCMA uses 0.66 cu ft for an 80 lb bag of preblended grout)
- Bags by the core rule = cores to fill ÷ cores per bag from NCMA Table 4 (3.6 for 6 in, 2.7 for 8 in, 2.2 for 10 in, 1.8 for 12 in units)
The two bag counts differ: NCMA’s Table 4 fills fewer cores per bag than the volume alone suggests. If you are filling from bags, plan on the larger number.
Worked example
A 40 × 4 ft wall of 8 in block, grouted solid:
- Wall length: 40 ft
- Wall height: 4 ft
- Block width (nominal): 8 in block
- Grouted cells: Every cell (solid grouted)
- Bagged grout yield: 0.66 cu ft per bag
The calculator gives:
- Grout needed: 57.8 cu ft (2.14 cu yd)
- Bags by volume: 88 bags at 0.66 cu ft each
- Bags by the NCMA core rule: 134 × 80 lb bags for 360 cores (2.7 cores per bag)
- Rate used: 36.1 cu ft per 100 sq ft of wall (includes 3% waste)
160 sq ft × 36.1 cu ft per 100 sq ft = 57.8 cu ft, or 2.14 cu yd. Grouting every 48 in instead would need only 6.1 cu ft per 100 sq ft, about 9.8 cu ft.
Material and waste notes
- Bond beams (horizontal grouted courses) need extra grout that Table 3 does not include. NCMA gives about 2 linear feet of 8 in bond beam per 80 lb bag (Table 5).
- Lightweight blocks absorb more water from the grout, and pumping wastes a different amount than bucketing, so actual use varies (NCMA TEK 4-2A).
- NCMA does not recommend grouting 4 in units, so they are not included.
- Which cells to grout and where the rebar goes are design decisions. Follow your plans or local code.
Frequently asked questions
How much concrete to fill cinder blocks?
For 8 in block grouted solid, about 36 cu ft per 100 sq ft of wall (1.34 cu yd). For 12 in block it is about 59 cu ft per 100 sq ft.
Can I use regular concrete to fill block cores?
Masonry walls are normally filled with grout, a fluid mix made for filling cells around reinforcement. Use what your plans or building department specify.
How many bags of grout per block?
For 8 in units NCMA’s Table 4 gives about 2.7 cores per 80 lb bag, so a block with both cores filled takes about 0.75 of a bag.
Sources
Last reviewed: 25 September 2026. The calculation is covered by automated tests with known answers taken from the sources above. Found an error? Please let us know.