Masonry calculator: CMU and brick units, mortar, and grout

Estimating concrete block: what the numbers actually are

Concrete block and CMU are the same thing. CMU stands for concrete masonry unit, and the two names are used interchangeably on drawings, in specs, and on supplier quotes. This page and the calculator above use CMU, so read every CMU reference as concrete block if that is the term your documents use.

The nominal block everyone means by default is 8 in x 8 in x 16 in. Nominal includes the mortar joint, which is why the arithmetic is clean: a nominal 8 x 16 face is 128 square inches, and 144 / 128 gives 1.125 blocks per square foot of wall. That single rate answers most concrete block questions. A 1,000 sf wall is 1,125 blocks before waste.

Estimating concrete block is therefore three steps, not one:

1. Wall area. Length times height per wall segment, openings deducted.
2. Unit count. Area times 1.125 for standard 8 x 8 x 16 block, times a different rate for other unit sizes.
3. Everything that is not the block. Mortar, grout, reinforcing, lintels, bond beams, and the accessories, which are covered further down and are where most concrete block estimates go wrong.

The block count is the easy part. The rest of this page is the rest of the job.

How masonry square footage is actually taken off

Masonry is taken off as square feet of wall face, separately for every unit type and every wall thickness, then converted to units with a rate per square foot. You scale each wall for length off the plan and for height off the sections or elevations, multiply, deduct the openings, and stop. The conversion from area to block or brick is arithmetic. The judgement is all in how you segmented the walls and what you did with the openings.

Segment by wall type, not by elevation. A single wythe 8 in CMU wall and a CMU backup carrying brick veneer cover the same square feet of elevation and are nowhere near the same money. Corners, returns, jambs, control joints, lintels, and bond beams come off in linear feet as separate lines, because they do not scale with area.

The formulas

Gross wall area (sf) = wall length (ft) x wall height (ft) Net wall area (sf) = gross wall area minus openings deducted Units laid = wall area (sf) x units per sf Units to order = units laid x (1 + waste percent / 100) CMU mortar (80 lb preblended bags) = units laid / 16 Brick mortar, net (cu ft) = (brick laid / 1,000) x cubic feet of mortar per 1,000 brick Brick mortar with waste (cu ft) = net mortar x (1 + mortar waste percent / 100) Brick mortar (80 lb bags) = mortar with waste / selected product yield in cu ft per 80 lb bag, rounded up Grout (cu ft) = (wall area / 100) x cubic feet of grout per 100 sf of wall Grout (cu yd) = grout cubic feet / 27, and grout bags = grout cubic feet / 0.66

Why standard CMU is exactly 1.125 units per square foot

Derive it rather than take it on faith. A standard block is nominally 8 in high by 16 in long on its face, so that face covers 8 x 16 = 128 square inches. A square foot is 12 x 12 = 144 square inches. One square foot of wall therefore takes 144 / 128 = 1.125 units, which is 112.5 units per 100 square feet.

It comes out exact because the dimension is nominal. The unit itself is manufactured 7 5/8 in by 15 5/8 in, and the 3/8 in mortar joint at the bed and the head makes up the missing 3/8 inch in each direction. Unit plus joint equals the 8 by 16 module, so you divide a square foot by the module rather than by the block. That is also why the rate does not change with wall thickness: a 12 in block still presents an 8 by 16 face.

Modular brick works the same way. A modular brick face is nominally 2 2/3 in high by 8 in long, so 8 x 2.6667 = 21.333 square inches, and 144 / 21.333 = 6.75 brick per square foot, or 675 per 100 square feet.

Now cross-check both against the published tables. NCMA TEK 4-2A Table 1 lists 119 conventional 8 x 16 units per 100 square feet and states that the figure includes about 5 percent waste: 112.5 x 1.05 = 118.1, which rounds to their 119. BIA Technical Notes 10 Table 4 lists 675 modular brick per 100 square feet not including waste, and separately says to add at least 5 percent for breakage: 6.75 x 1.05 = 7.09 per square foot. That is where the field figure of 7 brick per square foot comes from, and it is why you will see 6.75 and 7 quoted for the same wall by people who are both right.

The published rates this calculator uses

• CMU units: 1.125 per sf, derived above. NCMA TEK 4-2A, Estimating Concrete Masonry Materials, Table 1 gives 119 units per 100 sf with about 5 percent waste included.
• Modular brick: 6.75 per sf. BIA Technical Notes 10, Dimensioning and Estimating Brick Masonry, Table 4 gives 675 per 100 sf, not including waste.
• Brick mortar: BIA Technical Notes 10, Table 4, modular brick: 8.1 cu ft per 1,000 brick at a 3/8 in joint, which is 5.5 cu ft per 100 sf of wall, and 10.3 cu ft per 1,000 at a 1/2 in joint. Both are theoretical quantities that exclude waste.
• CMU mortar: NCMA TEK 4-2A, Table 2: one 80 lb bag of preblended mortar lays about 16 conventional units and one 3,000 lb bulk bag lays about 420. For site mixing, the same table gives about 240 units per ton of masonry sand, and one 70 lb bag of masonry cement lays about 30 units. All of these assume face shell bedding, which is why they do not change with unit width.
• Grout: NCMA TEK 4-2A, Table 3, cubic feet of grout per 100 sf of wall for two-core hollow units, with 3 percent waste included. For 8 in units: 36.1 with every cell grouted, 18.1 at 16 in on center, 12.1 at 24 in, 9.1 at 32 in, 7.3 at 40 in, and 6.1 at 48 in. Wider units take more, so a 12 in wall at 48 in on center is 9.9.
• Grout bag yield: NCMA TEK 4-2A: an 80 lb bag of preblended grout yields about 0.66 cu ft. Bond beam grouting is a separate quantity, and TEK 4-2A Table 5 gives about 2.0 linear feet of 8 in bond beam per 80 lb bag.
• Waste: BIA Technical Notes 10 says to add at least 5 percent to net brick quantities for breakage and waste, and 15 to 25 percent to net mortar quantities. NCMA TEK 4-2A Table 1 has about 5 percent built into its unit counts already, so do not add 5 percent to a number that already carries it.

What the clean square footage misses

Openings deductions are handled inconsistently between bidders. Deducting every opening in full, deducting nothing on the argument that jambs and heads still cost labor, and deducting only openings above a stated size are all in use on real bids. So two masons can submit different square footages for the same elevation without either of them making an arithmetic error, and the general contractor leveling the bids cannot see why the numbers differ. State the rule. Put the deduction basis, the opening count, and the total area deducted into your clarifications. This calculator makes the choice explicit with a deduction rule selector, and it prints gross and net so you can quote either basis and say which one you used.

Waste varies by bond pattern and by how cut up the elevation is. BIA recommends adding at least 5 percent waste to its net brick quantities; NCMA's conventional CMU unit table already includes about 5 percent. The calculator starts from net unit rates and adds the selected unit waste once. Adjust that allowance for soldier courses, rowlock sills, header courses, and short returns. BIA Technical Notes 10 Table 6 quantifies part of this for brick: common bond with full headers every fifth course adds one fifth to the brick count and one fifteenth to the mortar. The rest of it, the breakage and the cutting, is shop specific. Pull the ordered quantity against the taken off quantity on your last several jobs and use that spread. Do not adopt anyone else's single percentage, including ours.

Grout depends on wall area, unit geometry, and which cells are specified for grouting. At a fixed unit width and grouted-cell spacing, the calculator scales cell grout with wall area. The structural drawings and masonry specification determine the grouting pattern, which can include cells without reinforcing, and the bond beam requirements. Price those requirements as well as the measured area. Here is the arithmetic that catches people. Change an 8 in wall from 48 in on center to 24 in on center and the square footage does not move at all, but grout goes from 6.1 to 12.1 cubic feet per 100 square feet, so it roughly doubles. Go solid grouted and it is 36.1, about six times the 48 in on center quantity. Read the S sheets and the masonry specification before you put a grout number in a bid, then say in the proposal what bar spacing and grouted cell count you priced.

Worked example

Take the calculator defaults: one 60 ft long by 12 ft high wall of 8 in CMU, 180 sf of openings deducted (six windows at 5 ft by 6 ft), vertical bars at 48 in on center, and 5 percent unit waste.

Gross wall area is 60 x 12 = 720 sf. Deduct the 180 sf of openings and the net area is 540 sf. At 1.125 units per square foot that is 540 x 1.125 = 607.5 units laid, and adding 5 percent waste gives 638 units to order. Mortar covers the units actually laid, so 607.5 / 16 = 38 bags of 80 lb preblended mortar. Grout at 48 in on center in an 8 in wall is 6.1 cubic feet per 100 square feet, so 5.4 x 6.1 = 32.9 cubic feet, which is 1.22 cubic yards or 50 bags of 80 lb preblended grout.

For the same net wall area in modular brick veneer, the unit and mortar rates change: 540 x 6.75 = 3,645 brick laid, 3,828 brick to order at 5 percent waste, and mortar of 3,645 / 1,000 x 8.1 = 29.5 cubic feet at a 3/8 in joint, before mortar waste. With the calculator's illustrative 20 percent mortar waste and 0.7 cubic feet per 80 lb bag yield, use 29.5245 x 1.20 = 35.4294 cubic feet, then round 35.4294 / 0.7 up to 51 bags. At a 1/2 in joint, net mortar rises to 37.5435 cubic feet and the same waste and yield assumptions give 65 bags. The bag count already includes mortar waste. Replace the example yield with the selected product's published mixed-mortar yield; an 80 lb bag does not have one universal yield. Grout is not in that scope unless the backup wall is yours as well.

From quantity to a priced line

The block count, the mortar, and the grout are the quantity half of a masonry bid. The priced line multiplies each quantity by your own unit cost for material, mortar and grout, scaffolding, and layup labor, at your own productivity. That is the step Ruh automates. It reads the drawing set, measures the scope wall by wall, and prices the measured quantities against your own price book, with every line traceable back to the sheet it came from, and your estimator reviewing the result before it goes out.

For the unit itself see the CMU glossary entry, and for the scope boundaries that decide whether the grout, the lintels, and the cavity flashing are even yours, read how to bid masonry as a subcontractor.