Concrete Block Calculator

HomeMath counts blocks by course: a standard block with its mortar joint covers 8 × 16 in, so the wall takes its height ÷ 8 in courses, rounded up because a part course at the top is a course of cut blocks, of length ÷ 16 in blocks each. The waste allowance covers broken and cut blocks. For core fill, HomeMath takes the open cores of a two-core block, its actual size less ASTM C90's minimum 1 1/4 in face shells and a 1 in web (HomeMath's assumption for a typical block), through the full 8 in height of each course. In metric, HomeMath converts meters and centimeters exactly (1 in = 2.54 cm) and shows the result in cubic meters, liters and square meters. Metric blocks differ by country, so there the courses come from your block's face with its joint in millimeters (presets for the 440 × 215 mm (the UK and Ireland) and 390 × 190 mm (Australia, New Zealand and Canada) blocks with a 10 mm joint), the core fill from the maker's data sheet and the blocks per mortar bag from your bag.

The published rules it uses: concrete masonry unit sizes; US customary units; metric conversion; premixed bag yields; mortar bag coverage. Their sources, and how HomeMath tests every result, are on the about page.

Count by courses. A standard block is 15 5/8 × 7 5/8 in on its face, and with a 3/8 in mortar joint it fills 16 × 8 in of wall. For a 32 ft wall 6 ft high:

1. Courses: 6 × 12 ÷ 8 = 9, rounded up if it isn't a whole number.
2. Blocks per course: 32 × 12 ÷ 16 = 24.00.
3. Blocks: 9 × 24.00 = 216.
4. Waste: 216 × 1.10 = 237.6, so buy 238.

When the height is whole courses, a shortcut gives the same count: a block covers 128 square inches of wall and a square foot is 144, so the wall takes 144 ÷ 128 = 1.125 blocks per square foot. 192 sq ft × 1.125 = 216. The count depends only on the 8 × 16 in face, so it holds for blocks 4, 6, 8, 10 or 12 in wide.

A part course still takes a full row of blocks, cut down. A 20 × 3.5 ft wall is 5.25 courses high, so the calculator counts 6 courses of 15: 90 blocks before waste, where the wall area alone would give 78.8. At corners, measure one wall to the outside and the next from the inside face, or the corner blocks are counted twice.

The installed price is on the block wall cost calculator, the footing on the concrete wall calculator, and dry-stacked walls on the retaining wall block calculator.

About 0.30 cu ft per standard block when every core is filled. Real blocks with thicker, tapered shells take a little less; check the yield on your grout or mix bag. Many walls fill only the cores that hold rebar, while retaining walls and some foundations are filled solid; your plans or code decide, so scale the full-fill amount down.

Walls are filled solid or only in the cores that hold vertical rebar, at corners, ends, openings and set spacings along the wall; your plans or your local code say which, so not every core needs concrete. For the 20 × 4 ft wall:

The blocks to buy × your price per block. With an example $2.50 a block, the 30 × 6 ft wall's 223 blocks cost $558, or $3.10 per square foot of wall. A full wall budget also has the footing (the concrete wall calculator sizes it), mortar, core fill and rebar, cap blocks and labor. For the installed price of the whole wall, use the block wall cost calculator.

The calculator divides the blocks to buy by the blocks one mortar bag lays, rounding up. It starts with 12 blocks per 80 lb bag, from Quikrete Mortar Mix's data sheet, so the 30 × 6 ft wall's 223 blocks take 19 bags of 80 lb mortar.

Coverage differs by brand and mix, so type the number printed on your bag.

Nominal sizes are what the block takes up in the wall with its joint, so walls laid out in multiples of 8 in need no cut blocks. Half blocks (8 × 8 × 8 nominal) finish the ends of alternate courses; count each as half a block. Other widths and block types are in our guide to concrete block types.

It depends on the block: 1 ÷ its face with the joint, in meters. With a 10 mm joint, a 440 × 215 mm block lays 9.88 per m², so a wall of US blocks (12.11 per m²) takes 23% more.

Switch the units to metric and the calculator takes the wall in meters or centimeters, the openings in square meters and your block's face with its joint in millimeters. The courses are whole rows of the block's height with its joint (225 mm for a 440 × 215 mm block), so a height that isn't a whole number of them is built with a cut course at the top, and counted as one. For core fill, type the fill per block in liters from the maker's data sheet; solid blocks have none. The US block preset fills in its own, about 8.5 L per block.