Cinder block calculator

Enter the length and height of the wall and the block size. We count the courses and the blocks, the bags of mortar and the grout for filled cores.

6 courses of 15 blocks: 90 blocks in the wall, order 95 with 5% extra, and about 7 bags of 80 lb mason mix.

Blocks per sq ft: 1.13 on 8 x 16 in centers
Height as built: 4.0 ft in 6 courses
Mortar: 7 bags at 13 blocks a bag, no waste
Grout: None
Block cost: $226.10 for 95 blocks at $2.38 each

The block price is the 8 x 8 x 16 in concrete block at The Home Depot, Hamilton Mill store, read Nov 6, 2026, before tax; a block yard may charge less by the pallet. Mortar and grout are not priced. Corners and pilasters take a few more blocks than a straight run. A wall that holds back soil is a retaining wall with its own rules.

Holding back a slope? Retaining wall calculator

Segmental wall blocks, caps and drain gravel.

Planning quantities. A block wall needs a footing below the frost line, and rebar and grout where your plans or the building department say. Walls that hold back soil follow retaining wall rules.

How the cinder block calculator works

Enter the length and height of the wall, any doors or openings, and the block size. The cinder block calculator counts the courses and the blocks in each course, takes out the openings, adds the extra for breakage, and gives the bags of mortar and the grout for any cores you fill.

Courses and blocks per course

A standard block is 8 in tall and 16 in long with its joint. A 4 ft wall is 48 / 8 = 6 courses and a 20 ft wall is 240 / 16 = 15 blocks a course: 90 blocks. A height that is not a multiple of 8 in rounds up to the next full course, so plan the wall on the 8 in module.

Mortar

At 13 blocks a bag, the 90 blocks are 7 bags of 80 lb mason mix. Half-high blocks have more joints per square foot, so allow more.

Grout and rebar

Cores with vertical rebar are filled with grout. With bars every 48 in, every third cell is filled; solid grouting fills all of them. The 20x4 ft wall solid grouted takes 23.4 cu ft.

Cinder blocks by wall size

Wall	Courses	Blocks	To order, +5%	80 lb mortar bags
10 ft long, 2 ft high	3	24	26	2
20 ft long, 3 ft high	5	75	79	6
20 ft long, 4 ft high	6	90	95	7
10 ft long, 10 ft high (100 sq ft)	15	120	126	10
40 ft long, 6 ft high	9	270	284	21
88 ft around a 20x24 ft garage, 8 ft high	12	792	832	61

Block walls around a patio

A low block wall makes a seat wall or a planter along a patio, or the base for an outdoor kitchen. For a wall that holds back a slope, the retaining wall calculator counts segmental blocks, caps and drain gravel. The footing under a block wall is poured concrete; the concrete slab calculator works for a strip footing if you enter its width and depth.

Where the numbers come from

Block sizes are nominal, width x height x length; the unit is 3/8 in smaller each way so that with a 3/8 in joint it lays up on 8 x 16 in centers. The mortar yield is the Quikrete Mason Mix data sheet: each 80 lb bag will lay up to 37 standard bricks or 13 standard 8 x 8 x 16 in blocks. The core volumes and the 5% extra blocks are editorial figures. The block price is a shelf price for the standard 8 x 8 x 16 in block at The Home Depot, Hamilton Mill store ($2.38 each, read Nov 6, 2026); other sizes and yards vary, so we price only that block.

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Questions

Anything else? Write to us or see every calculator.

Questions people ask

A standard 8x8x16 block covers 8 x 16 in of wall with its mortar joint, so there are 1.125 blocks per square foot. Count it by course for a real wall: the height in inches over 8 is the courses, the length in inches over 16 the blocks per course. A 20 ft wall 4 ft high is 6 courses of 15, 90 blocks, and 95 to order with 5% extra.

112.5 standard 8x8x16 blocks by area, 119 with 5% extra. A real wall rounds up to whole courses and blocks: 10 ft by 10 ft is 15 courses of 8, 120 blocks. Half-high 8x4x16 blocks take twice as many.

An 80 lb bag of Quikrete Mason Mix lays up to 13 standard 8x8x16 blocks, the data sheet says, with no allowance for waste. The 20x4 ft wall's 90 blocks take about 7 bags; buy one or two more for a first wall.

About 0.26 cu ft per standard 8 in block for its two cores (editorial; the block maker's sheet gives the exact figure). Solid grouting the 20x4 ft wall takes 23.4 cu ft, 0.87 cu yd. Most walls grout only the cells that hold rebar.