Block / CMU Calculator
Count concrete block for a wall: enter wall length and height, deduct openings, set a waste factor, and get the block count, courses, and mortar bags for standard 8×8×16 CMU — then print it as a material order sheet. Coverage is pure geometry (1.125 block per square foot of wall); the mortar yield is a planning figure you should round up on. Free, no login.
Wall (8×8×16 CMU)
Materials
≈1.125 block/ft² and ≈3 bags type-S per 100 block — planning figures; confirm against the spec & product data.
Block Calculator — Material Order Sheet
Prepared with NORDIX — nordixhq.com/tools/block-calculator
| Wall: 40 × 8 ft (320 ft² net) | Openings: 0 ft² | Waste: 5% |
| Material | Qty | Unit | Notes |
|---|---|---|---|
| 8×8×16 CMU block | 378 | blocks | 12 courses, waste included |
| Mortar, type S | 12 | 70 lb bags | ≈3 bags / 100 block |
Method: 1.125 block/ft² (8×8×16 CMU with 3/8" joints), waste included; ≈3 bags type-S mortar per 100 block (running bond). Empirical planning figures — confirm against the project spec and product data; excludes reinforcement, grout, and accessories.
How this calculator works
Coverage for standard block is geometry, not a rule of thumb: a nominal 8×8×16 unit plus its 3/8" joints occupies an 8" × 16" face module — 0.89 ft² — so:
block = net area × 1.125 × (1 + waste%) · 1.125 = 144 ÷ (8 × 16)
Openings are deducted before counting; courses divide the wall height by the 8" nominal course (7-5/8" block + 3/8" bed joint), rounded up. Mortar is the part that is not geometry: the calculator carries roughly three 70 lb bags of type-S per 100 block (running bond, 3/8" joints) — a planning figure that moves with joint tooling, weather, and what drops off the board, so round up on the order. Note that 6" and 12" block share the same 8×16 face module, so the count per square foot is identical; only mortar and grout quantities change.
Worked example
A 40 ft long × 8 ft high wall, no openings, 5% waste:
- Area: 40 × 8 = 320 ft².
- Block: 320 × 1.125 × 1.05 = 378 → 378 block.
- Courses: 8 ft ÷ 8" course = 12 courses.
- Mortar: 378 ÷ 100 × 3 = 11.34 → 12 bags (70 lb), rounded up.
Enter the same wall above (40 × 8 ft, 5% waste) to reproduce it, then print the order sheet.
Reference: block and mortar per wall area (planning figures)
Standard 8×8×16 CMU at 1.125 block/ft², before waste, with mortar at the ≈3-bags-per-100 planning yield. Add your waste factor on top and confirm yields against the spec and product data.
| Net wall area | Block (before waste) | Mortar (70 lb bags) |
|---|---|---|
| 100 ft² | 113 | 4 |
| 200 ft² | 225 | 7 |
| 500 ft² | 563 | 17 |
| 1,000 ft² | 1,125 | 34 |
Frequently asked questions
How many concrete blocks per square foot of wall?
1.125 blocks per square foot for standard 8x8x16 nominal CMU. Each block plus its 3/8-in. mortar joints occupies an 8x16-in. face module — 0.89 square feet — so figure 112.5 block per 100 square feet of wall before waste. That is the coverage this calculator uses. Note that 6-in. and 12-in. block share the same 8x16 face module, so the count per square foot is identical; only the mortar and grout quantities change.
How much mortar do I need per 100 block?
Plan on roughly three 70 lb bags of masonry cement mortar per 100 standard block laid in running bond with 3/8-in. joints — the yield rule this calculator uses. Actual usage moves with joint tooling, weather, and how much drops off the board, so treat it as an estimate and round up on the order.
How many courses of block for an 8 foot wall?
Twelve. A CMU course is 8 in. nominal — a 7-5/8-in. block plus a 3/8-in. bed joint — so divide the wall height in inches by 8. The calculator rounds up to whole courses: a 9 ft wall shows 14 courses because 13.5 rounds up.
What waste factor should I use for concrete block?
5% is a reasonable default for straight running-bond walls, and it is what the calculator starts with. Go higher — 7 to 10% — when the wall has lots of corners, piers, cut block, or openings, or when block gets handled several times on site. Waste is a judgment call, not a fixed number; your breakage history is the best guide.
How do I handle doors and windows?
Enter the total opening area in square feet and the calculator deducts it from the wall area before counting block. It does not add back lintel block, jamb units, or sash block around the openings — take those off the plans separately.
Does this calculator figure grout, rebar, or wall ties?
No — this tool covers block count, courses, and bed-joint mortar only. Cell-fill grout is figured in the mortar & grout calculator (about 0.45 cubic feet per fully grouted block), and vertical steel, joint reinforcement, and ties come off the wall sections and structural notes.
Method: coverage of 1.125 block/ft² is exact geometry for nominal 8×8×16 CMU with 3/8" joints (144 ÷ (8 × 16)); courses at 8" nominal, rounded up. The mortar yield of ≈3 bags (70 lb) type-S per 100 block in running bond is an empirical planning figure, not a standard — actual usage varies with the crew and conditions. Excluded entirely: lintel, jamb, and sash units at openings, joint reinforcement, vertical steel, grout, and ties — take those off the plans. Cell-fill grout is figured in the Mortar & Grout Calculator.
Pair with the Mortar & Grout Calculator for cell-fill grout, the Brick Calculator for veneer counts, or the Construction Calculator for the footing concrete under the wall.