The reinforced-wall version of block counting. Enter wall size, CMU thickness and how the cells are grouted to get blocks, grout in cubic yards, and mortar, the three lines a CMU order needs.
CMU Block Calculator
Blocks count at 1.125 per sq ft for every thickness. What changes with thickness and fill spacing is the grout, that is this tool’s specialty.
CMU blocks to order
Grout factors include an allowance for bond beams in partially grouted walls. This page assumes blocks are ordered with the same 10% waste as the other block tools, the order count above includes it; grout is figured on exact wall area.
A CMU block calculator counts blocks at 1.125 per square foot and adds the reinforced-wall materials: grout and mortar. A 20 × 8 ft wall in 8 in CMU needs 198 blocks to order, about 6 mortar bags, and, fully grouted, roughly 1.60 yd³ of grout. Choose your thickness and fill pattern above.
How to Calculate CMU Blocks and Grout
CMU, concrete masonry unit, is the engineer’s name for the same block family, and CMU walls are usually the reinforced kind: vertical rebar in grouted cells, horizontal bond beams, real structural work. Counting those walls takes three numbers, not one, blocks, mortar, and grout volume that swings wildly with the fill pattern. This CMU block calculator produces all three from wall size, block thickness and the grouting schedule on your drawing.
The Formula
Grout (yd³) = wall area × grout factor for thickness × fill factor
8 in CMU fully grouted ≈ 1.0 yd³ grout per 100 sq ft · Mortar ≈ 3 × 60 lb bags per 100 blocks
Grout factors per square foot of wall: 6 in ≈ 0.007, 8 in ≈ 0.010, 10 in ≈ 0.013, 12 in ≈ 0.016 yd³ when every cell is filled. Partial grouting scales by the filled-cell share, with bond beams included in the factors used here, verify against your grout supplier’s table for large pours.
Worked Example: 20 × 8 ft Wall, 8 in CMU, Fully Grouted
Blocks: 160 sq ft × 1.125 = 180 exact, 198 ordered. Grout: 160 × 0.010 = 1.60 yd³, order 1.75 yd³ to cover pump priming and cell irregularities. Mortar: 6 bags. The same wall grouted at vertical cells 24 in o.c. plus bond beams needs only about 0.40 yd³, the fill pattern is a 4× swing in grout, which is why it is an input, not an assumption.
Grout Volume per 100 sq ft of Wall (Fully Grouted)
| CMU thickness | Grout per 100 sq ft | Typical use |
|---|---|---|
| 6 in | ≈ 0.7 yd³ | Partitions, light structural |
| 8 in | ≈ 1.0 yd³ | Foundations, standard structural walls |
| 10 in | ≈ 1.3 yd³ | Retaining, heavier loads |
| 12 in | ≈ 1.6 yd³ | Tall retaining, high-load walls |
Figures are for walls with all cells filled. A bond beam course (usually every 4 ft of height or at the top) adds grout even in ‘partially grouted’ walls, the fill factors in this calculator include a bond-beam allowance so the order is not short.
Why Grout Orders Need Their Own Margin
Grout disappears into places the drawing doesn’t show: a cracked cell web, a cleanout left open, pump lines that hold a quarter yard before the first cell fills. Order grout about 10% over the calculated figure on small walls and confirm the plant’s minimum, on the 1.60 yd³ example, a 1.75–2 yd³ ticket is the professional order. Blocks carry the standard 10% cutting and breakage allowance.
How to Measure and Calculate: Step by Step
- Take wall length, height, CMU thickness and the grouting schedule from the drawing.
- Enter length and height; select thickness and the matching fill pattern.
- Note blocks to order (includes 10% waste) and mortar bags.
- Round grout up to the plant’s increment and add pump priming on pumped pours.
- Cross-check rebar for the grouted cells with the Rebar Calculator.
Worked Example 2: 60 × 10 ft Foundation Wall, Cells at 24 in o.c.
Area = 600 sq ft. Blocks: 675 exact, 743 ordered. Grout at the 24 in factor: 600 × 0.010 × 0.25 = 1.50 yd³, less grout than the small fully-grouted example wall, on nearly four times the wall. Mortar: 23 bags. This is the arithmetic that makes partial grouting the default wherever the engineer allows it.
Common Quantities at a Glance: Cheat Sheet
| Job / quantity | Result |
|---|---|
| 100 sq ft, 8 in, full grout | 113 blocks · 1.0 yd³ grout |
| 100 sq ft, 8 in, cells @ 24 in | 113 blocks · 0.25 yd³ grout |
| 20 × 8 ft, 8 in, full grout | 198 ordered · 1.60 yd³ grout |
| 20 × 8 ft, 12 in, full grout | 198 ordered · 2.56 yd³ grout |
| Bond beam course, per 100 ft of 8 in wall | ≈ 0.35 yd³ grout |
| Mortar, any CMU wall | ≈ 3 × 60 lb bags per 100 blocks |
Practical Tips From the Job
Grout in lifts the code allows (typically up to 5 ft pours with consolidation, per TMS 602) and reconsolidate, a tall single pour blows out cells and starves the top. Keep cleanouts open at the base of grouted cells until inspection. And schedule the grout pump and the inspector for the same morning; both are cheaper than a second pour.
Common Mistakes to Avoid
- Ordering grout from the fully-grouted table when the wall is partial, or the reverse.
- Forgetting bond beams in a ‘vertical cells only’ grout estimate.
- Counting blocks from actual dimensions and double-counting joints.
- Grouting cells that contain no rebar because the layout drifted.
- Skipping cleanouts, then discovering debris at the base of a filled cell.
What It Costs and How to Order Smart
On reinforced work the grout and steel rival the block cost: the example wall’s 1.6 yd³ of grout plus pump can exceed its 6 bags of mortar many times over. Price the three lines separately, blocks each, grout per yard delivered and pumped, mortar per bag, and use the fill-pattern figure to challenge any quote that assumes full grouting by default.
Who Uses This Calculator?
Builders pricing foundation packages use the three-line output directly. Contractors ordering grout pumps live on the fill factors. Engineers checking a submittal use the per-100-sq-ft table. Architects detailing a CMU wall use the thickness rows, and experienced homeowners building a reinforced shop wall get the full order in one place.
CMU Block Calculator FAQs
How much grout do I need for a CMU wall?
Fully grouted, an 8 in CMU wall takes about 1.0 yd³ of grout per 100 sq ft of wall. Grout only the vertical reinforced cells and the figure drops sharply: roughly 0.35 yd³ per 100 sq ft at 16 in spacing, 0.25 at 24 in, including bond beams. Select your pattern above for your wall’s exact figure.
How many CMU blocks do I need for a 20×8 wall?
The same as any 8×8×16 block wall: 160 sq ft × 1.125 = 180 blocks exact, 198 to order with 10% waste, plus about 6 bags of mortar. CMU thickness (6, 8, 10, 12 in) does not change the block count, the face size is constant, it changes the grout volume and the block weight.
What does CMU stand for?
Concrete masonry unit, the technical name for concrete block. ‘CMU’ is the term on drawings, specs and structural plans, while ‘block’ or ‘cinder block’ is yard language. When a drawing says 8 in CMU, partially grouted, it is asking for exactly the three quantities this calculator returns: units, mortar and grout.
What is the difference between fully and partially grouted CMU?
Fully grouted fills every cell, maximum strength and weight, used for high-load and some below-grade walls. Partially grouted fills only the cells containing rebar plus bond beam courses, cutting grout volume by 65–90% on typical spacing. The engineer chooses; the cost difference is large enough that the choice appears in every bid.
How much grout is in one 8 inch block?
A standard 8×8×16 CMU has two cells totalling roughly 0.24 ft³ of core space. That matches the wall rate: fully grouted 8 in walls work out at about 1 yd³ of grout per 112 blocks laid (100 sq ft of wall). As a site shortcut, figure roughly a cubic foot of grout for every 4 blocks in a fully grouted 8 in wall.
Do CMU walls always need rebar in the grouted cells?
Grouted cells without rebar add weight but little strength; the grout’s job in structural walls is to bond the rebar to the masonry so they act together. Vertical bars sit in the filled cells per the drawing’s spacing, with horizontal steel in bond beams. Grouting a cell with no bar is normally only done where the spec calls for solid grouting.
What strength grout is used in CMU?
Grout for masonry is typically specified at a minimum 2,000 psi and must be fluid enough to fill cells completely, it is a high-slump mix, closer to pea-gravel concrete than to mortar. It is batched and tested as its own material; do not substitute leftover slab concrete unless the spec allows it and the aggregate size suits the cells.
How high can grout be poured in one lift?
Masonry standards (TMS 602) allow grout pours up to about 5 ft for standard grout spaces, with consolidation and reconsolidation, and taller pours under defined conditions with cleanouts and inspection. Your mason and inspector work to the project spec, the practical point for ordering is to schedule grout in lift-sized quantities, not one wall-sized load.
How accurate is this CMU block calculator?
Block counts are exact at the standard rate. Grout factors are the industry working figures per thickness and include a bond-beam allowance for partial patterns; real cells vary slightly by manufacturer. On large walls, confirm the factor against your block supplier’s grout table and keep the 10% grout margin, pumps and cleanouts always take their share.
Related Calculators
Sources used for standards and conversions: National Ready Mixed Concrete Association (NRMCA) guidance on ordering and yield; American Concrete Institute (ACI) practice for mix and placement; Portland Cement Association (PCA) design and control guidance; US manufacturers’ printed yields (80 lb bag = 0.60 ft³). Depths, sizes and spacings set by your local building code govern wherever they differ from the general figures here.
Disclaimer: Results are estimates for planning and ordering. Check the quantities with your supplier before you order. Footings, walls, columns, beams and any other load-bearing work need a licensed engineer to look them over.