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Estimate blocks, mortar, sand, and user-supplied material costs for a wall.
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Masonry block calculator guide
A concrete block wall is estimated from its net face area and the face area of one block including its mortar joint. This calculator multiplies wall length by height in feet, subtracts any door and window openings, and divides by the effective face of a block: the nominal 16 × 8 in unit is entered as its actual 15 5/8 × 7 5/8 in body plus a 3/8 in mortar joint, so the tool adds the joint allowance you specify to the block length and height you enter. It then adds a waste percentage for cuts and breakage and rounds up to whole blocks. Mortar is estimated as a fraction of the wall volume and converted to bags, with sand per bag alongside. Bond pattern and mortar type are recorded for the supplier but do not change the quantity. The result covers a single-wythe wall; footings, rebar, grout fill for cores, and lintels are separate.
Net wall area (sq ft) = length × height − openings. Block face (sq ft) = (block length + joint) ÷ 12 × (block height + joint) ÷ 12. Blocks = ⌈net area ÷ block face × (1 + waste ÷ 100)⌉. Mortar (ft³) = net area × block depth ÷ 12 × mortar fraction.
Worked example: a 20 ft long, 8 ft high wall with no openings has a net area of 20 × 8 = 160 sq ft. Each 16 × 8 in block plus a 0.375 in joint occupies (16.375 ÷ 12) × (8.375 ÷ 12) = 1.365 × 0.698 = 0.952 sq ft, so the base count is 160 ÷ 0.952 = 168 blocks. With 10% waste, 168 × 1.10 = 184.8, rounded up to 185 blocks. Wall volume is 160 × (8 ÷ 12) = 106.67 ft³; at a 15% mortar fraction that is 16 ft³ of mortar, or 32 bags at 0.5 ft³ each, with 32 × 1.5 = 48 ft³ of sand. The calculator displays 185 blocks.
Wall and opening dimensions are feet; block dimensions and the joint are inches; waste and mortar fraction are percentages. The 16 × 8 × 8 in defaults are nominal sizes, which already include one joint, so entering them with a 0.375 in joint slightly overcounts and acts as extra allowance; enter 15.625 × 7.625 for a tighter estimate. Mortar volume is shown in cubic feet and cubic yards; sand is cubic feet.
The masonry block calculator returns a quantity to buy, not a guarantee of coverage. Substrate condition, waste from cuts, spillage, and settling all push real consumption above the theoretical figure, which is why most trades order a margin on top. Check the coverage rate printed on the product you actually purchase, because it varies between brands and mixes. On this page the figure rests entirely on wall length, wall height, door openings, door width, door height, window openings, window width, window height, block length, block height, block depth, bond / layout pattern, mortar mix / specification, mortar joint allowance, block waste allowance, mortar fraction of wall volume, mortar bag yield, sand per mortar bag, block price, mortar bag price and sand price, so start there if the masonry block calculator returns something you did not expect.
Good to know: forgetting to enter openings overstates blocks, but so does entering a door count without its width and height. The 15% mortar fraction is a planning figure; hollow blocks with face-shell bedding use less. Blocks are sold per unit or by the cube of 90 (8 in) or 120 (4 in), so round the purchase to a cube. Corners need alternating half blocks, and a wall taller than 4 ft usually needs reinforced and grouted cores, which this tool does not estimate.
Construction quantities are planning estimates. Confirm product yield, waste, site conditions, structural requirements, and local code with the supplier or qualified professional.
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How it works
Estimate blocks, mortar, sand, and user-supplied material costs for a wall. This tool explains the calculation so you can adjust the assumptions to match your situation.
Worked example
With Wall length = 20 ft · Wall height = 8 ft · Door openings = 0 · Door width = 3 ft · Door height = 7 ft · Window openings = 0 → 185 blocks (recommended masonry quantity including waste). Change an input above and this example updates with your numbers.
Common questions
A 20 ft long, 8 ft high wall of standard 16 × 8 in blocks needs about 168 blocks before waste and 185 with a 10% allowance. Subtract door and window openings if the wall has them, and add half blocks for corners.
A standard 16 × 8 in nominal block covers 0.889 sq ft including its joint, so a wall needs 1.125 blocks per square foot, or 112.5 blocks per 100 sq ft. Add 5–10% for cuts and breakage.
Rule-of-thumb figures are about 3 cubic feet of mortar per 100 blocks with 3/8 in joints, or one 80 lb bag of premixed mortar for every 25–35 blocks. This calculator uses a 15% fraction of wall volume, which gives 32 half-cubic-foot bags for 185 blocks.
The most common CMU is nominally 16 in long, 8 in high, and 8 in deep. Actual dimensions are 15 5/8 × 7 5/8 × 7 5/8 in so that a 3/8 in mortar joint brings each unit back to the nominal module. Widths of 4, 6, 10, and 12 in are also standard.
Yes. Enter the number and size of each opening and the calculator removes their area before dividing by the block face. A 3 × 7 ft door removes 21 sq ft, about 24 blocks; a 3 × 4 ft window removes 12 sq ft, about 14 blocks.