Free Live Calculators

Cinder Block Calculator

Calculate how many cinder blocks you need for a wall. Cinder blocks are the same as concrete masonry units (CMU) — this calculator covers all standard sizes.

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Openings (doors & windows)

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Cinder block wall diagram showing the block, waste, and mortar calculations for a 100 square foot wall
Verified example: a 100 sq ft wall at 1.125 standard blocks per sq ft needs 113 blocks before waste, 124 blocks with 10% waste, and about eleven 80 lb mortar bags. Block coverage, waste, and mortar values verified against the calculator logic and CMU references cited on this page.

How to Use This Calculator

  1. 1

    Enter wall dimensions

    Enter wall length and height in feet. For multiple walls, add their lengths together.

  2. 2

    Select block size and options

    Choose Standard 8×8×16 for most walls. Select mortar joint thickness (3/8-inch standard) and waste factor (10% recommended). Enter door and window dimensions to subtract opening areas.

  3. 3

    Get your material list

    Results show blocks needed (with and without waste), number of courses, mortar bags, and optional cost estimate.

What Each Value Means

Courses (rows)
Horizontal rows of blocks in the wall. For standard 8×8×16 blocks with 3/8-inch mortar joints: courses = wall height in inches ÷ 8.375.
Waste Factor (percent)
Additional blocks beyond the calculated minimum to account for cuts, breakage, and irregular edges. Standard recommendation: 10%.

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Frequently Asked Questions

Are cinder blocks the same as concrete blocks?
Yes — in modern construction, cinder blocks and concrete blocks are the same product. 'Cinder block' is an older term that persisted after manufacturers stopped using coal cinders as aggregate. Today all blocks sold as 'cinder blocks' are concrete masonry units (CMU) made with Portland cement. The calculator works for both terms.
How many cinder blocks do I need per square foot?
Standard 8×8×16 cinder/concrete blocks with a 3/8-inch mortar joint require approximately 1.125 blocks per square foot of wall area. For 100 sq ft of wall: 100 × 1.125 = 113 blocks (rounded up). Always add 10% for waste from cuts, breakage, and irregular edges.
How much mortar do I need for cinder blocks?
Plan for approximately 8.5 bags of 80 lb pre-mixed mortar per 100 cinder blocks. This covers both bed joints (horizontal) and head joints (vertical). For a 200-block wall, order about 17 bags. If mixing from scratch, use 1 bag masonry cement plus 3 bags sand for approximately the same coverage.
What sizes do cinder blocks come in?
Standard sizes: 8×8×16 (most common structural use), 4×8×16 (interior partition walls), 6×8×16 (moderate load bearing), 12×8×16 (retaining walls), and 8×8×8 (half block for filler courses). All sizes with an 8×16 face require the same 1.125 blocks per square foot. Half blocks (8×8 face) need 2.25 per square foot.
How do I calculate how many courses of cinder blocks I need?
Courses (horizontal rows) = wall height in inches ÷ 8.375 (standard block height + 3/8-inch joint). For an 8-foot wall: 96 ÷ 8.375 = 11.46 → 12 courses. This calculator shows the number of courses automatically.

References & Sources

  1. [1]
    USDA National Agricultural Library (opens in new tab)

    Supports: Evidence used for how to build a cinder block raised garden bed, including related formulas, definitions, or reference values.

    Verified

  2. [2]
    U.S. Bureau of Labor Statistics — Construction Materials Price Index (opens in new tab)

    Supports: Evidence used for cinder block cost: price per block, per pallet & project estimates, including related formulas, definitions, or reference values.

    Verified

  3. [3]
    U.S. Bureau of Labor Statistics — Masonry Workers Wages (opens in new tab)

    Supports: Evidence used for cinder block wall cost guide: materials, labor, and budget, including related formulas, definitions, or reference values.

    Verified

  4. [4]
    ASTM C90 — Standard Specification for Loadbearing Concrete Masonry Units (opens in new tab)

    Supports: Evidence used for 8×8×16 cinder block coverage, courses, and mortar reference, including related formulas, definitions, or reference values.

    Verified