CMU block calculator: blocks, mortar and grout.
Enter each CMU wall, deduct openings, choose the unit size and get block counts, mortar bags and grout cubic yards for a partially or fully grouted wall, with every assumption editable.
Send one plan set. See what the AI extracts and what it flags for review. No obligation.
- 8×16, 8×8 or 4×16 units
- Partial or full grout
- Formula shown live
1 · CMU walls length × height
2 · Units & openings
3 · Mortar & grout
4 · Prices (optional)
Live formula
Save your results
Copy these results, then add your approved sample files in the trial brief.
Estimates only. Check every default against your spec, supplier data and crew records before you bid.
Standard formulas, shown on the page.
Nothing hidden. These are the same steps an estimator runs on a takeoff sheet.
1. Net wall area
Multiply each wall's length by its height, add them up, and subtract door, window and louver openings.
2. Blocks per square foot
Nominal unit dimensions include the 3/8-in mortar joint, so the face area of a nominal 8 × 16 unit is 128 sq in, or 0.889 sq ft. That gives 1.125 blocks per square foot.
3. Mortar
Mortar is usually carried as bags per hundred block or blocks per bag. The default is an editable assumption; use the yield printed on the mortar you buy.
4. Grout
Take the share of wall area that is grouted (from the structural notes: cells at bars, bond beams, jambs) and multiply by grout volume per square foot of fully grouted wall.
Every default is cited or editable.
Replace any of these with your spec, supplier data sheet or job-cost history. The calculator recalculates instantly.
| Input | Default | Source |
|---|---|---|
| Block face area (8 × 16 nominal) | 0.889 sq ft → 1.125 blocks/sq ft | Geometry of nominal dimensions (8 × 16 in ÷ 144) |
| Block waste | 5% | Editable assumption |
| Blocks per mortar bag | 30 | Editable assumption. Mortar yield varies by product and joint profile; use the bag's published yield. |
| Grout per sq ft, fully grouted | 0.26 cu ft | Editable assumption for 8-in hollow units. Use the manufacturer's core volume or your own records. |
| Wall area grouted | 25% | Editable assumption. Set from the reinforcing layout in the structural drawings. |
Three masonry checks the calculator can't make.
Bond beams and lintels
Bond beam and lintel units replace standard units and are fully grouted. Count their courses separately so the grout volume and unit mix are right.
Grout spacing from the notes
Vertical grouted cells are usually set by the reinforcing spacing in the structural general notes, e.g. every cell with a bar. The grouted percentage follows from that, not from habit.
Specials and corners
Corner, bullnose, half and sash units are priced differently. Most estimators count them from elevations and corners rather than from area.
From calculator to bid: get the quantities off the drawings.
Speed is easy to promise. Defensible numbers are the job, so RenderDraw keeps the estimator in control of every quantity that gets priced.
- Source on every row. Each quantity keeps its source sheet, location and reviewer decision.
- Lowest confidence first. The review queue shows the drawing tile with the detection highlighted and the extracted value.
- Uncertain items flagged, not hidden. Anything the AI can't confirm goes to the estimator rather than being guessed.
- Nothing priced before approval. Rows move on to pricing only after they are accepted.
Questions estimators ask
How many CMU blocks per square foot?
For a nominal 8 × 16 in unit, 1.125 blocks per square foot of wall, or 112.5 per 100 sq ft, before waste. For 8 × 8 in units, 2.25 per square foot.
How do you calculate CMU blocks for a wall?
Multiply wall length by height, subtract openings, divide by the face area of one nominal unit (0.889 sq ft for 8 × 16), and add waste.
How much grout does a CMU wall need?
Multiply the grouted share of the wall area by the grout volume per square foot of fully grouted wall for your unit size. The 0.26 cu ft default for 8-in units is an editable assumption; check the manufacturer's data.
How many bags of mortar per 100 blocks?
It depends on the mortar product, joint thickness and waste. Use the yield printed on the bag; the calculator default of 30 blocks per bag is an editable assumption.
Does this replace a masonry takeoff?
No. It is a quick check. A real masonry takeoff also counts bond beams, lintels, specials, reinforcing, control joints and accessories from plans, elevations and the structural notes.
See what the AI reads on your own drawings.
Send one representative concrete plan set. RenderDraw reviews it and follows up with what the AI extracted and what it flagged for review. Your files remain private while the request is assessed, and there is no obligation.
- Upload foundation plans, slab plans, footing and column schedules, typical details, and the concrete and masonry spec sections.
- RenderDraw reviews the set and the scope you want tested.
- We follow up with extracted quantities, flagged items and next steps.