How much concrete does it take to fill one cinder block?

About 0.22 cubic feet (6.2 litres) for the two cells of an 8 x 8 x 16 in block, the figure behind the 80 lb bag of core-fill grout that fills three. A 12 in block takes about 0.4 cubic feet, a 6 in block about 0.15.

How many bags of concrete to fill 100 cinder blocks?

41 bags of 80 lb (0.6 cubic feet each) for every cell of 100 standard 8 in blocks: 24.2 cubic feet including 10% for spills and the mortar droppings that take room in the cells. That is 0.9 cubic yards, which is where a short load from the ready-mix plant starts to beat mixing bags.

How much concrete to fill a 20 ft block wall?

Every cell of a 20 x 4 ft wall (90 blocks) takes 21.8 cubic feet, 37 bags of 80 lb. With bars every 32 in and a bond beam on top it is 8.2 cubic feet and 14 bags, because only one cell in four is filled below the top course.

Do I fill every cell or only the ones with rebar?

Only the cells with bars, plus the bond beam course, unless the plan says fully grouted. Retaining walls and walls below grade are often fully grouted; a fence wall usually has bars every 32 or 48 in. The cells are 8 in apart, so 32 in spacing fills one in four and 48 in one in six. Use the calculator's spacing menu to see the difference.

Can I use regular concrete mix to fill cinder blocks?

Yes, for a few blocks: an 80 lb bag of concrete mix yields 0.6 cubic feet, close to the 0.65 of core-fill grout, and the tables use that figure. Keep the mix wet enough to flow around the bars and rod it down. Grout is a wetter mix, coarse grout with pea gravel and fine grout with sand only, made to flow into the cells without voids; for a whole wall, order grout or a fine-aggregate mix from the plant.

When should I order a truck instead of bags?

Around a cubic yard, which is 45 bags of 80 lb: a 40 x 8 ft wall with every cell filled needs 146 bags, 3.23 cubic yards, and a truck or a grout pump makes sense. The concrete cost guide has the short-load fees.

How much concrete to fill cinder blocks? (per block, per 100, per wall)

About 0.22 cubic feet for both cells of a standard 8 x 8 x 16 in block: an 80 lb bag of core-fill grout yields 0.65 cubic feet and fills three. Filling every cell of 100 blocks takes 24.2 cubic feet with 10% extra, 41 bags of 80 lb concrete or 0.9 cubic yards from the truck. The tables give the grout per block for each width, per 100 blocks, and for walls from 10 to 40 ft with every cell filled or bars every 16 to 48 in.

Open the concrete block calculator

Grout per block by width

The 8 in figure is the makers' own: an 80 lb bag of core-fill grout yields 0.65 cubic feet and fills about three standard blocks. The other widths are scaled from the size of their cells and can be changed in the concrete block calculator if your block's data sheet says otherwise. Per 100 blocks includes 10% extra and uses 80 lb bags of 0.6 cubic feet.

Every cell filled, hollow concrete blocks, 16 in long
Block	Grout per block	Per 100 blocks	80 lb bags per 100	Cubic yards per 100
6 x 8 x 16 in	0.15 cu ft	16.5 cu ft	28	0.61
8 x 8 x 16 in	0.22 cu ft	24.2 cu ft	41	0.9
10 x 8 x 16 in	0.3 cu ft	33 cu ft	55	1.22
12 x 8 x 16 in	0.4 cu ft	44 cu ft	74	1.63

Grout for a wall, every cell filled

Standard 8 x 8 x 16 in block, no openings, 10% extra. Blocks are courses times blocks per course, rounded up.

8 in block, every cell filled
Wall	Blocks	Grout	80 lb bags	Cubic yards
10 x 4 ft	48	11.6 cu ft	20	0.43
10 x 6 ft	72	17.4 cu ft	30	0.65
10 x 8 ft	96	23.2 cu ft	39	0.86
20 x 4 ft	90	21.8 cu ft	37	0.81
20 x 6 ft	135	32.7 cu ft	55	1.21
20 x 8 ft	180	43.6 cu ft	73	1.61
40 x 4 ft	180	43.6 cu ft	73	1.61
40 x 6 ft	270	65.3 cu ft	109	2.42
40 x 8 ft	360	87.1 cu ft	146	3.23

Grout for a wall with bars every 32 or 48 in

Cells are 8 in apart along the wall, so bars every 32 in fill one cell in four and bars every 48 in one in six. Both tables add a bond beam: the top course filled solid, with two horizontal bars. The bars column is the vertical bars, one per filled cell with one at each end.

8 in block, bars every 32 in, bond beam on top
Wall	Blocks	Vertical bars	Grout	80 lb bags
10 x 4 ft	48	5	4.4 cu ft	8
10 x 6 ft	72	5	5.8 cu ft	10
10 x 8 ft	96	5	7.3 cu ft	13
20 x 4 ft	90	9	8.2 cu ft	14
20 x 6 ft	135	9	10.9 cu ft	19
20 x 8 ft	180	9	13.6 cu ft	23
40 x 4 ft	180	16	16.3 cu ft	28
40 x 6 ft	270	16	21.8 cu ft	37
40 x 8 ft	360	16	27.2 cu ft	46

8 in block, bars every 48 in, bond beam on top
Wall	Blocks	Vertical bars	Grout	80 lb bags
10 x 4 ft	48	4	3.5 cu ft	6
10 x 6 ft	72	4	4.5 cu ft	8
10 x 8 ft	96	4	5.5 cu ft	10
20 x 4 ft	90	6	6.7 cu ft	12
20 x 6 ft	135	6	8.5 cu ft	15
20 x 8 ft	180	6	10.3 cu ft	18
40 x 4 ft	180	11	13.3 cu ft	23
40 x 6 ft	270	11	16.9 cu ft	29
40 x 8 ft	360	11	20.6 cu ft	35

The same 20 x 6 ft wall at every spacing the calculator offers, so you can see what the spacing decides:

20 x 6 ft wall of 8 in block, bond beam where bars are spaced
Bar spacing	Cells filled	Vertical bars	Grout	80 lb bags
Every cell	100%	31	32.7 cu ft	55
16 in	50% + top course	16	18.2 cu ft	31
24 in	33% + top course	11	13.3 cu ft	23
32 in	25% + top course	9	10.9 cu ft	19
48 in	17% + top course	6	8.5 cu ft	15

Metric: 440 x 215 x 215 mm hollow block

The 215 mm hollow block has about 9 litres of cells, in the same proportion of its volume as the 8 in unit; check your maker's figure. 100 blocks with every cell filled take 990 litres with 10% extra, or 83 bags of 25 kg concrete (12 L each). Cells are 225 mm apart, so bars every 900 mm fill one cell in four.

1.8 m high wall of 215 mm hollow block, 25 kg bags
Wall	Blocks	Bars	Grout	25 kg bags
3 x 1.8 m, every cell	56	15	554 L	47
3 x 1.8 m, bars every 900 mm	56	5	191 L	16
6 x 1.8 m, every cell	112	28	1,109 L	93
6 x 1.8 m, bars every 900 mm	112	8	381 L	32
10 x 1.8 m, every cell	184	46	1,822 L	152
10 x 1.8 m, bars every 900 mm	184	13	626 L	53

Before you pour

Clean the cells as you lay: mortar that squeezes into a cell you will grout takes room and stops the grout reaching the bottom. The 10% in the tables covers normal droppings, not a cell full of them.
Wet the block first in hot weather and pour in lifts of about 4 ft (a storey pour needs cleanouts at the bottom), rodding or vibrating each lift so the grout wraps the bar.
Mixing bags for more than about 40 of them is a long day; the yard of concrete guide gives the truck price, and the concrete calculator does the footing under the wall.
Blocks, mortar and the cost of the whole wall are in the block wall cost guide; the sequence of the job in building a block wall.

Frequently asked questions

How much concrete does it take to fill one cinder block?: About 0.22 cubic feet (6.2 litres) for the two cells of an 8 x 8 x 16 in block, the figure behind the 80 lb bag of core-fill grout that fills three. A 12 in block takes about 0.4 cubic feet, a 6 in block about 0.15.
How many bags of concrete to fill 100 cinder blocks?: 41 bags of 80 lb (0.6 cubic feet each) for every cell of 100 standard 8 in blocks: 24.2 cubic feet including 10% for spills and the mortar droppings that take room in the cells. That is 0.9 cubic yards, which is where a short load from the ready-mix plant starts to beat mixing bags.
How much concrete to fill a 20 ft block wall?: Every cell of a 20 x 4 ft wall (90 blocks) takes 21.8 cubic feet, 37 bags of 80 lb. With bars every 32 in and a bond beam on top it is 8.2 cubic feet and 14 bags, because only one cell in four is filled below the top course.
Do I fill every cell or only the ones with rebar?: Only the cells with bars, plus the bond beam course, unless the plan says fully grouted. Retaining walls and walls below grade are often fully grouted; a fence wall usually has bars every 32 or 48 in. The cells are 8 in apart, so 32 in spacing fills one in four and 48 in one in six. Use the calculator's spacing menu to see the difference.
Can I use regular concrete mix to fill cinder blocks?: Yes, for a few blocks: an 80 lb bag of concrete mix yields 0.6 cubic feet, close to the 0.65 of core-fill grout, and the tables use that figure. Keep the mix wet enough to flow around the bars and rod it down. Grout is a wetter mix, coarse grout with pea gravel and fine grout with sand only, made to flow into the cells without voids; for a whole wall, order grout or a fine-aggregate mix from the plant.
When should I order a truck instead of bags?: Around a cubic yard, which is 45 bags of 80 lb: a 40 x 8 ft wall with every cell filled needs 146 bags, 3.23 cubic yards, and a truck or a grout pump makes sense. The concrete cost guide has the short-load fees.

How many concrete blocks do I need for a wall?
8x8x16 blocks per square foot and for walls from 10x4 to 40x8 ft with 5% waste, mortar volume, and the metric 440 x 215 mm block per square metre.
How much does a cinder block wall cost? (materials per wall and per square foot)
Blocks, mortar and grout priced for walls from 10x4 to 40x8 ft at 2026 shelf prices, materials per square foot, what grouting adds, and HomeGuide's installed range.
Building a block wall: courses, rebar, grout and mortar for a 20 ft wall
The material list for a CMU wall in order: footing, courses, half blocks, bars every 32 or 48 in, grouted cells, bond beam and mortar, with counts for 4 to 8 ft walls.
How much does a cinder block garage cost? (blocks, mortar, grout and slab for 1, 2 and 3 car)
Blocks, mortar and grout for 1 to 3 car block garages, 12x20 to 36x24 ft, 8 ft walls, doors and windows taken off, plus the 4 in slab, at 2026 prices.

Last updated 2026-09-15. Figures are planning estimates from typical product data: check the yield, size or coverage printed on what you buy and round up.