Enter the size of a concrete block wall, or the number of blocks, and choose which cells you will fill. The calculator gives the volume of core-fill grout and the number of 80 lb bags, or the cubic yards for a ready-mix or pump order.
How to use the block fill calculator
- Choose wall size or number of blocks. For wall size, enter the length and height of the block wall.
- Pick the cells to fill. Retaining walls and foundations are often solid grouted; reinforced walls may only fill the cells with rebar, every 32 or 48 in.
- Keep 0.217 ft³ per block for standard 8 in hollow block, or enter a figure from your block or grout supplier.
- Add a few percent for spills and grout that runs into joints.
Block fill formulas
Blocks = wall area (ft²) ÷ 0.889 ft² (one 8 × 16 in block face, with joints) Fill (ft³) = blocks × fill per block × share of cells filled × (1 + extra %) Bags (80 lb, 0.65 ft³) = fill ÷ 0.65, rounded up Cubic yards = fill ÷ 27
Quikrete’s data sheet for Core-Fill Grout says one 80 lb bag yields about 0.65 ft³ and fills the cores of about three standard 8 × 8 × 16 in blocks. That works out to about 0.217 ft³ per block, the default here.
Worked example: a 40 × 4 ft wall, solid grouted
- Wall area: 40 × 4 = 160 ft². Blocks: 160 ÷ 0.889 = 180 blocks.
- Fill: 180 × 0.217 = 39.1 ft³; with 5% extra, 41.0 ft³.
- Bags: 41.0 ÷ 0.65 = 63.1, so 64 bags of 80 lb core-fill grout.
- As ready-mix: 41.0 ÷ 27 = 1.52 yd³.
Filling only every fourth cell (32 in on center) takes a quarter as much: about 10.3 ft³, or 16 bags.
Core fill by wall area
For 8 in hollow block, fully grouted, with 5% extra:
| Wall area | Blocks | Fill | 80 lb bags | Cubic yards |
|---|---|---|---|---|
| 50 ft² | 57 | 12.8 ft³ | 20 | 0.47 |
| 100 ft² | 113 | 25.6 ft³ | 40 | 0.95 |
| 200 ft² | 225 | 51.3 ft³ | 79 | 1.90 |
| 400 ft² | 450 | 102.5 ft³ | 158 | 3.80 |
| 800 ft² | 900 | 205.1 ft³ | 316 | 7.60 |
Bags or ready-mix?
Bagged core-fill grout is easiest for short walls and a few reinforced cells. Past about a cubic yard, ordering grout from a ready-mix plant and placing it with a pump or a chute is usually cheaper and faster than mixing 40 or more bags. Masonry grout is a fluid mix made for filling cells; ask the plant for grout or a pea-gravel mix rather than ordinary concrete.
Tips for filling block cores
- Follow the plans. Engineered walls specify which cells get rebar and grout, and the grout type.
- Clean the cells. Knock off mortar fins that stick into the cores so the grout can flow to the bottom.
- Consolidate the grout. Rod or vibrate it to remove voids, as the grout maker directs.
- Count the blocks too. Use the concrete block calculator for blocks and mortar.
Questions
How much concrete does it take to fill a cinder block?
About 0.217 ft³ for a standard 8 × 8 × 16 in hollow block, based on Quikrete’s figure of three blocks per 0.65 ft³ bag.
How many blocks does a bag of core fill fill?
About three 8 in blocks per 80 lb bag of core-fill grout.
How many yards of grout to fill 100 blocks?
100 × 0.217 = 21.7 ft³, or about 0.8 yd³ before extra.
Do all cinder block cores need to be filled?
No. Many walls only fill the cells with rebar. Solid grouting is used where the plans call for it, such as some retaining walls and below-grade walls.
Sources
- Core-Fill Grout (Coarse) No. 1585-07 data sheet, Quikrete.
Used for: 80 lb bag yields about 0.65 ft³ and fills the cores of about three 8 × 8 × 16 in blocks. - NIST Guide to the SI, Appendix B.8: Factors for units listed alphabetically, National Institute of Standards and Technology.
Used for: Inch and foot definitions; cubic foot to cubic yard and cubic metre.