How much concrete to fill 100 cinder blocks?
Filling every core of 100 standard 8 inch blocks takes about 32.1 cubic feet of grout or concrete, using CMHA’s table (3% waste included). In 80 lb bags of concrete mix that is 54 bags; in 80 lb core-fill grout it is 48.
How to work it out
- 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
- ÷ 0.6 cu ft per 80 lb bag = 54 bags
A hundred blocks is about 89 sq ft of wall. Filled solid, that wall holds about 1.2 cubic yards of grout — far more than most people expect, which is why the bag count is worth checking before you start.
Adjust for your project
- Grout volume (incl. 3% waste)
- 32.1 cu ft (1.19 cu yd)
- Per block
- 0.32 cu ft
100 blocks by width, every core filled (concrete mix)
| Block width | Bags to buy | Grout volume (incl. 3% waste) |
|---|---|---|
| 6 in block | 38 bags | 22.8 cu ft |
| 8 in block | 54 bags | 32.1 cu ft |
| 10 in block | 70 bags | 41.8 cu ft |
| 12 in block | 88 bags | 52.4 cu ft |
Bags or a truck?
At 32 cu ft, this is 54 bags of 80 lb concrete mix or 48 of core-fill grout. That is a lot of mixing to pour into narrow cores a bucket at a time. Many masons order grout as ready-mix and pump it into the cores in lifts instead; ask your supplier, since structural grout has its own specification.
Quikrete’s Core-Fill data sheet estimates a bag fills about 3 blocks, which would make it 34 bags. The difference is that CMHA’s figure counts the full core volume plus waste. If you buy by Quikrete’s count, buy a few extra and return what is left.
Partial grouting
Grouting only the cores at a spacing — common with vertical rebar — cuts the grout a lot: every 16 in uses half as much, every 48 in about a sixth. The variants below show 16 in and 48 in. For the blocks themselves, see 8×8×16 block actual size; for a single block, how much grout to fill one 8 inch block.
Different size? Use the full Block Fill (Grout) Calculator.
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)
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 grout to fill 100 blocks with cores 16 inches apart?
About 16.1 cubic feet: 24 bags of 80 lb core-fill grout.
How much grout for 100 blocks with cores 48 inches apart?
About 5.42 cubic feet: 8 bags of 80 lb core-fill grout.
How much concrete to fill 100 twelve-inch blocks?
About 52.4 cubic feet: 88 bags of 80 lb concrete mix.
Other common sizes
- How much grout to fill one 8 inch block — About 0.32 cu ft per block (about half an 80 lb bag)
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.