Concrete Block Calculator
Use this concrete block calculator to count the CMU blocks in a mortared wall from its length, height and the openings you subtract. It starts with the standard 16 × 8 in nominal face, which is 1.125 blocks per square foot, and also gives courses, blocks per course, mortar bags and cost. This page is for mortared concrete masonry walls; for dry-stacked segmental walls use the retaining wall calculator, and for concrete, rebar, gravel and floor area see the concrete, rebar, gravel and square footage calculators.
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Blocks to buy (with waste)
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Blocks before waste
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Wall area to build
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Courses
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Blocks per course
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Blocks per area
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Mortar bags (80 lb)
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Estimated cost
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A standard 8 × 8 × 16 in block is a nominal size: the actual block is 7⅝ × 7⅝ × 15⅝ in and the ⅜ in mortar joint brings its face to 16 × 8 in, or 0.889 sq ft, so a wall needs 144 ÷ (16 × 8) = 1.125 blocks per square foot. Blocks = (wall area − openings) × blocks per area, plus the waste allowance, rounded up (5% is an adjustable allowance, not a standard). Mortar: about 12 blocks per 80 lb bag for 8 × 8 × 16 blocks, from manufacturer data sheets (one sheet says up to 13); it changes with joint thickness and the mason. Grout for filled cores, rebar and the footing are not included.
Retaining Wall Calculator · Concrete Calculator Bags · Rebar Calculator · Gravel Calculator · Square Footage Calculator · Sand Calculator
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How it works
- How many concrete blocks do I need for a wall?
- Multiply wall length by height to get the area, subtract doors and windows, then multiply by 1.125 blocks per square foot for the standard 16 × 8 in face. A 20 ft × 4 ft wall is 80 sq ft, so 90 blocks (15 blocks per course × 6 courses) before any waste allowance.
- Does block thickness change how many blocks I need?
- No. 4, 6, 8, 10 and 12 in wide blocks all have the same 16 × 8 in nominal face, so the count per square foot is the same; thickness changes weight, price per block and wall strength. Only the face size matters here, so edit it if you use half-height or other special units.
- How much mortar do I need for concrete blocks?
- Manufacturer data sheets list about 12 standard 8 × 8 × 16 in blocks laid per 80 lb bag of mortar mix (one sheet says up to 13). The field starts at 12 and you can edit it. Joint thickness and waste change the real figure, so keep a spare bag.
- Does the calculator include grout, rebar or the footing?
- No. It counts blocks and mortar for the wall only. Grout-filled cores and rebar depend on your plans and local code, and a wall normally sits on a footing sized from those plans; use the rebar and concrete calculators for quantities and check your drawings.
- How is this different from the retaining wall calculator?
- This page is for mortared concrete masonry (CMU) walls laid with a ⅜ in joint and counted by face area. The retaining wall calculator is for dry-stacked segmental blocks with caps, buried courses, base and gravel backfill. Use the one that matches how you build.