Concrete Block (CMU) Calculator

Wall length and height are feet. The nominal 8-by-16-inch module includes the joint and covers 8/9 ft². The mortar output uses QUIKRETE Type S Mason Mix No.

1136’s published yield of up to 13 standard blocks per 80-lb bag. Actual joints, waste and unit geometry can require more; another product needs its own yield.

Walls with many openings, pilasters or different block heights change the count. Mortar consumption varies with the mason and joint thickness. Structural block walls need reinforcement and grout to code.

Footings and frost depth matter for foundations. Weather affects curing and safety.

Blocks needed from wall length

Wall length	20
Wall height	8
Blocks needed	180
80-lb Type S Mason Mix bags (13 blocks/bag)	14

Common error: Forgetting that the block is nominal. The real block is slightly smaller than its nominal size, and the joint fills the difference, so the wall area still divides evenly.

Concrete Block (CMU): formula

Whole blocks = ceiling(wall area × 1.125), using the 8×16 nominal face; 80-lb Type S Mason Mix bags = ceiling(blocks ÷ 13)

QUIKRETE Type S Mason Mix No. 1136: product yield

Concrete Block (CMU): changing Wall length

Blocks needed: assumed Wall length scenarios.
Wall length	Blocks needed	80-lb Type S Mason Mix bags (13 blocks/bag)
16	144	12
18	162	13
20 (example)	180	14
22	198	16
24	216	17

Concrete Block (CMU): compare input ranges

Concrete Block (CMU) Calculator: Blocks needed with each input moved on its own, every other input held at the worked-example value.
Input	Tested from	To	Blocks needed: low input	Blocks needed: high input	Swing
Wall height	7	9	158	203	45 (25%)
Wall length	18	22	162	198	36 (20%)

Concrete Block (CMU): individual input comparisons

Concrete Block (CMU) Calculator: change one input at a time; other values remain at the stated example.
Input	Value	Blocks needed	80-lb Type S Mason Mix bags (13 blocks/bag)
Wall length	16	144	12
	18	162	13
	20	180	14
	22	198	16
	24	216	17
Wall height	6	135	11
	7	158	13
	8	180	14
	9	203	16
	10	225	18

Blocks needed: Wall length against Wall height

Concrete Block (CMU): Blocks needed at combined Wall length and Wall height settings.
Wall length / Wall height	6	8	10
16	108	144	180
18	122	162	203
20	135	180	225
22	149	198	248
24	162	216	270

Concrete Block (CMU): values and definitions

Worked-example inputs and the results they produce for the Concrete Block (CMU) Calculator.
Quantity and definition	Value used
Wall length — Length of the block wall, in feet.	20
Wall height — Height of the block wall, in feet.	8
Blocks needed	180
80-lb Type S Mason Mix bags (13 blocks/bag)	14

Wall height: half and double

Concrete Block (CMU) scale comparison; assumed inputs.
Wall height	Blocks needed
4	90
8	180
16	360

Measure gross face area, subtract actual openings and distinguish modular count from special-unit scheduling. Mortar bags use the selected product’s published laying yield, while reinforcement and filled-cell grout require separate specifications.

Subtract door and window openings and add a small allowance for cuts. Confirm the mortar type your job requires, since bag yields differ.

See mortar on the mortar mix calculator, the footing on the footing size page, reinforcement on the rebar calculator and slab concrete on the concrete volume calculator. The paver and cubic yard pages cover other masonry, and the rectangle area calculator gives the wall area.

Does fourteen bags include construction waste?

No. It rounds 180/13 upward using the specified product’s up-to yield. Mortar lost during mixing or laying, different joints and another mix can change the purchase count.

Is a nominal block sixteen inches long without a joint?

No. Nominal modular dimensions include the joint. Match actual unit dimensions and the planned joint before estimating a nonstandard wall.

How many concrete blocks are in a square foot of wall?

About 1.125 standard 8 by 16 inch blocks per square foot, or roughly 1 block per 0.89 square feet.

How much mortar do I need for 100 blocks?

Use the selected mortar product’s coverage statement together with block size, joint thickness and the manufacturer’s installation assumptions. A bag count from another product or wall detail is not interchangeable. The linked product documentation and a project takeoff are more specific than a universal bags-per-hundred rule.

Should I order extra blocks?

Allow for cuts, breakage, corners, openings and the specified special units in the actual wall layout. The waste percentage is an order-planning assumption rather than a code-prescribed allowance. Check whole-unit counts and the supplier’s packaging before placing an order.

Concrete Block (CMU) Calculator