Concrete Block Fill Calculator
Find how many bags of grout fill the cores of your block wall.
Tell us about your wall
Your answer
That is 28.9 cubic feet, or 1.07 cubic yards.
This answer is a guide. Block walls with rebar and grout hold weight. Check your local building rules or ask a builder or engineer.
What it costs
Grout: $11.75 an 80 lb bag, the middle of only 2 stores (Oct 2026). Treat it as rough.
Quick answers
- One 8 in block, every core
- About 0.32 cubic feet, from CMHA's table (3% waste included).
- 100 sq ft of 8 in wall, solid
- 36.1 cubic feet. That is 61 bags of 80 lb grout, at 0.6 cubic feet a bag.
- One bag fills
- About 1.35 to 3 blocks (8 in), by source. See the list below.
- Grout or concrete?
- Grout is what the building code names. Quikrete says it needs a slump of 8 in or more.
- 4 in blocks
- CMHA says not to grout normal 4 in blocks.
How to work it out
- Measure the wall in feet. Length × height gives square feet.
- Pick the block width, and which cores you will fill.
- Find the cubic feet per 100 sq ft in the table below. Multiply by your square feet, then divide by 100.
- Divide by 0.6 cubic feet per 80 lb bag. Round up.
20 × 4 = 80 sq ft of 8 in wall
Every core: 36.1 cubic feet per 100 sq ft
80 × 36.1 ÷ 100 = 28.88 cubic feet
28.88 ÷ 0.6 = 48.1 → 49 bags
Grout for 100 sq ft of wall
The hollow holes in a block are its cores. CMHA, the Concrete Masonry & Hardscapes Association, gives this table. Find your block width across the top. Then go down to how far apart the filled cores are.
| Cores filled | 6 in | 8 in | 10 in | 12 in |
|---|---|---|---|---|
| Every core | 25.6 | 36.1 | 47 | 58.9 |
| Every 16 in | 12.8 | 18.1 | 23.5 | 29.5 |
| Every 24 in | 8.6 | 12.1 | 15.7 | 19.7 |
| Every 32 in | 6.4 | 9.1 | 11.8 | 14.8 |
| Every 40 in | 5.2 | 7.3 | 9.4 | 11.8 |
| Every 48 in | 4.3 | 6.1 | 7.9 | 9.9 |
Two-core hollow blocks. 3% waste is already in.
To use it, multiply by your wall's square feet. Then divide by 100. The calculator above does the same.
Grout per block, and per bag
A wall has 1.125 blocks per sq ft. So each block's share of the table is easy to work out.
| Width | Cubic feet per block | Blocks per bag (Table 3) | Blocks per bag (Table 4) |
|---|---|---|---|
| 6 in | 0.23 | 2.9 | 1.8 |
| 8 in | 0.32 | 2.1 | 1.35 |
| 10 in | 0.42 | 1.6 | 1.1 |
| 12 in | 0.52 | 1.3 | 0.9 |
The Table 3 column uses CMHA's own 0.66 cubic foot bag. Table 4 gives cores per bag; each block has 2 cores.
The answers don't agree
For an 8 in block, one 80 lb bag fills:
- About 2.1 blocks, by CMHA's Table 3.
- About 1.35 blocks, by CMHA's Table 4 (2.7 cores).
- About 2.4–2.7 blocks, says TCC.
- About 3 blocks, says Quikrete.
CMHA does not say why its two tables differ. The calculator uses Table 3. Table 4 would give more bags.
Bags differ a little too. TCC's grout bag makes 0.6 cubic feet. Quikrete's coarse grout makes 0.65, and its fine grout 0.68. CMHA says 0.66. We use 0.6, the smallest, so you don't run short.
Grout, not concrete mix
The US home building code (IRC R606.2.12) names grout for block cores. It must meet a standard called ASTM C476, or the code's own mix table.
Grout must be runny. Quikrete says it needs a slump of at least 8 in. Slump is how far wet mix sags when you lift off a test cone.
The IRC also lets you use Type M or S mortar as grout. Add enough water so it pours.
Quikrete lists its 5000 Concrete Mix as another choice for core fill. Grout is the material the building code names. If you use the concrete mix, check that your plans allow it.
Quikrete makes two grouts. Use coarse grout for cores over 4 in wide, and fine grout for cores under 4 in.
Before you fill the cores
- Check your plans for which cores to fill and where rebar goes.
- CMHA says not to grout normal 4 in blocks. The table starts at 6 in.
- Pour no more than 8 ft of grout at a time (a "lift"), as the IRC says.
- Quikrete's block wall guide puts rebar in every other core. That is one maker's project, not a code rule.
- Price the grout. We found $11.75 an 80 lb bag, the middle of only 2 stores ($10.50–$13.03). Treat it as rough.
Block walls with grout and rebar hold weight. Check your local building rules or ask a builder or engineer.
Questions people ask
How much concrete does it take to fill a cinder block?
About 0.32 cubic feet for an 8 in block with both cores filled. That comes from CMHA's table, with 3% waste in. Use core-fill grout, as the code names it.
How many bags does it take to fill a cinder block?
By CMHA's two tables, one 80 lb bag fills about 1.35 to 2.1 blocks, 8 in wide. TCC says 2.4–2.7, and Quikrete about 3.
How much concrete to fill a cinder block wall?
With every core full, 100 sq ft of 8 in wall takes 36.1 cubic feet. A 6 in wall takes 25.6, and a 12 in wall 58.9.
How much Quikrete to fill a cinder block?
Quikrete says one 80 lb bag of Core-Fill Grout fills about 3 blocks of 8 × 8 × 16 in. Quikrete lists its 5000 Concrete Mix as another choice for core fill. Grout is the material the building code names.
Can I use mortar to fill block cores?
The IRC allows Type M or Type S mortar as grout. Add enough water so that it pours.
How much grout for a 12 inch block?
About 0.52 cubic feet per block with both cores full. One 80 lb bag fills about 0.9 to 1.3 blocks, by CMHA's two tables. TCC says 1.5–1.9.
How high can I pour grout at one time?
The IRC says to pour no more than 8 ft of grout at a time. Each pour is called a lift.
Where our numbers come from
- Blocks, mortar, sand and core fill: Concrete Masonry & Hardscapes Association (TEK 04-02A)
- Blocks per bag by width: TCC Materials table (2025)
- Core-fill grout: Quikrete data sheet (coarse)
- Core-fill grout: Quikrete data sheet (fine)
- Block wall with rebar: Quikrete project page
- Grout for block walls: US home building code (IRC R606)
- Block size: Concrete Masonry & Hardscapes Association (TEK 02-02B)
- Grout bag price: 2 US stores (Oct 2026; few prices)
Made by BuildersCount. Last checked 3 Oct 2026.
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