Block fill calculator: grout or concrete for block cores
Enter the number of blocks (or the wall area), the block width and which cores get filled to see how much grout to buy.
Enter your measurements
- Grout volume (incl. 3% waste)
- 32.1 cu ft (1.19 cu yd)
- Per block
- 0.32 cu ft
- Quikrete’s own estimate
- About 3 blocks per 80 lb bag of Core-Fill grout — 34 bags
100 blocks ÷ 1.125 per sq ft × 36.1 cu ft per 100 sq ft (CMHA, 8 in, every core (solid grouted)) = 32.1 cu ft
÷ 0.68 cu ft per 80 lb bag = 48 bags
Quick answers for common sizes
| Example | Answer |
|---|---|
| How much concrete to fill 100 cinder blocks | About 32.1 cu ft: 54 bags of 80 lb concrete mix |
| How much grout to fill one 8 inch block | About 0.32 cu ft per block (about half an 80 lb bag) |
Bags by block width (count and spacing as above)
| Block width | Bags to buy | Grout volume (incl. 3% waste) | Per block |
|---|---|---|---|
| 6 in block | 34 bags | 22.8 cu ft | 0.23 cu ft |
| 8 in block | 48 bags | 32.1 cu ft | 0.32 cu ft |
| 10 in block | 62 bags | 41.8 cu ft | 0.42 cu ft |
| 12 in block | 77 bags | 52.4 cu ft | 0.52 cu ft |
Hollow concrete block has two open cores. Filling them with grout (or, for non-structural work, concrete) makes a wall solid and holds any vertical rebar in place. CMHA’s estimating guide (TEK 04-02A) tabulates the grout per 100 sq ft of wall by block width and how often cores are filled; those figures already include 3% waste.
Grout per 100 square feet of wall
| Cores filled | 6 in block | 8 in block | 10 in block | 12 in block |
|---|---|---|---|---|
| Every core (solid) | 25.6 | 36.1 | 47.0 | 58.9 |
| 16 in apart | 12.8 | 18.1 | 23.5 | 29.5 |
| 24 in apart | 8.6 | 12.1 | 15.7 | 19.7 |
| 32 in apart | 6.4 | 9.1 | 11.8 | 14.8 |
| 48 in apart | 4.3 | 6.1 | 7.9 | 9.9 |
grout (cu ft) = wall area (sq ft) ÷ 100 × table value wall area from blocks = blocks ÷ 1.125 bags = grout ÷ bag yield (Core-Fill ≈ 0.68 cu ft, concrete mix ≈ 0.60 cu ft)
Quikrete’s Core-Fill Grout data sheet gives a simpler estimate: one 80 lb bag (about 0.68 cu ft) fills the cores of about 3 standard 8×8×16 blocks. CMHA’s table, which counts the full core volume plus waste, works out to about 0.32 cu ft per block, or roughly 2 blocks per bag. The calculator uses CMHA’s figure and shows Quikrete’s for comparison.
Worked examples
- How much concrete to fill 100 cinder blocks — a solid-grouted 8 in wall.
- How much grout to fill one 8 inch block — the per-block number, and 12 in block.
Grout or concrete?
Masonry grout is made to be fluid and to fill narrow cores without voids, and structural walls usually call for it by name. Concrete mix with its larger stone can bridge and leave gaps in small cores. For a garden wall, a mailbox pillar or a fire pit, concrete mix is often used; for anything structural, follow your plans.
What you’ll need
- Drill mixing paddleBudget price
Mixes mortar, self-leveler, stucco and grout in a bucket. Use a low-speed, high-torque drill so the mix doesn’t fly.
See options on Amazon (opens in a new tab) - Mortar and concrete mixing tubBudget price
A wide, shallow tub for one or two bags at a time — easier to clean and to pull a hoe through than a wheelbarrow.
See options on Amazon (opens in a new tab) - Rebar tie wire and twisterBudget price
Ties bars together where they cross so the grid stays put while you pour.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How much concrete does it take to fill one cinder block?
About 0.32 cu ft for an 8 in block by CMHA’s table (including 3% waste) — roughly half an 80 lb bag of core-fill grout. Quikrete estimates its grout fills about 3 blocks per bag.
How many bags of concrete to fill 30 cinder blocks?
By CMHA’s figure, 30 eight-inch blocks hold about 9.6 cu ft: 17 bags of 80 lb concrete mix or 15 of core-fill grout. Quikrete’s core-fill estimate is 10 bags.
Do I fill every core in a block wall?
Only if your plans say so. Many walls are grouted only in the cores with rebar, at a spacing set by the design; fully grouted walls use about twice the grout of a wall grouted every 16 in.
Related guides
Sources
- CMHA (formerly NCMA) TEK 04-02A — Estimating concrete masonry materials (opens in a new tab) — Each 8×16 unit covers 8/9 sq ft, so 112.5 units per 100 sq ft (119 with 5% waste); grout per 100 sq ft by unit width and core spacing (Table 3); cores filled per 80 lb grout bag (Table 4); one 80 lb bag of preblended mortar lays about 16 CMU with face-shell bedding (Table 2).
- Quikrete Core-Fill Grout (Fine, No. 1585-08) data sheet (opens in a new tab) — Each 80 lb bag yields about 0.68 cu ft and fills the cores of about 3 standard 8×8×16 blocks.
- Quikrete Concrete Mix (No. 1101) data sheet (opens in a new tab) — Yields: 40 lb ≈ 0.30, 50 lb ≈ 0.375, 60 lb ≈ 0.45, 80 lb ≈ 0.60, 90 lb ≈ 0.675 cu ft; unit weight ≈ 140 lb/cu ft; for pours 2 in thick or more; 6–9 pints of water per 80 lb bag; control joints every 6–8 ft; cure 5 days at 70 °F or above, 7 days at 50–70 °F; protect from freezing for 48 hours.