Block Calculator — Concrete, CMU & AAC Blocks
Blocks, mortar or adhesive and grout for any block wall — IS 2185 and US CMU sizes.
Walls
Doors and windows to leave out
No openings — the whole wall is blockwork.
Blocks
Mortar
Mortar settings
Prices optional
Materials
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About the Block Calculator — Concrete, CMU & AAC Blocks
Work out how many blocks a wall needs and what goes with them. Choose a hollow or solid concrete block to IS 2185 (Part 1), an AAC block to IS 2185 (Part 3) or a US concrete masonry unit (nominal 8 × 16 in), or type your own size. Add every wall and take off the doors and windows; the calculator counts the blocks per m² from the block size and the joint, adds wastage and rounds up.
For block masonry in mortar it gives the wet mortar and the cement bags and sand for your mix; for AAC laid in thin-bed adhesive it gives the bags from the coverage printed on your bag; for CMU it uses the CMHA estimating tables for mortar materials and core-fill grout. Add prices to see the material cost.
How to use it
- Pick Metric or US units, then the block type and a standard size — or type the block length, height and width. Say whether the size is nominal (it includes one joint, as IS 2185-1 and CMU sizes do) or the actual block.
- Enter each wall as length × height (and how many), and add the doors and windows to leave out.
- Choose how the blocks are laid: cement–sand mortar (mix, joint and, for hollow blocks, the share of the bed face that takes mortar), thin-bed adhesive for AAC (the coverage from the bag) or the CMU mortar type and grout spacing.
- Check the wastage, add prices if you want the cost, and copy the result or download it as CSV.
Examples
10 mm joints · 1 : 6 mortar · 75 % of the bed face mortared · dry factor 1.33 · 15 % mortar wastage
28.11 m² × 12.5 per m² = 351.4 blocks → 369 with 5 % · joint space 0.415 m³ → wet mortar 0.311 m³ · cement 1.96 bags (buy 2) · sand 0.41 m³
8.17 blocks per m² → 245.1 net, 258 with 5 % · 4.5 m³ of blockwork — 5 bags if one bag lays 1 m³
112.5 units → 119 with 5 % waste · 1.81 batches of 1 ft³ cement + 1 ft³ lime + 6 ft³ sand · grout 36.1 ft³ (1.34 yd³)
Matches CMHA TEK 4-2A: 119 units per 100 ft², 62 units per batch of Type N mortar, 36.1 ft³ of grout per 100 ft² of fully grouted 8 in wall.
How the blocks are counted
Each block takes up its actual face plus one joint each way, so blocks per m² = 1 ÷ ((actual length + joint) × (actual height + joint)). A block named by its nominal size already includes the joint: an IS 2185-1 block of 400 × 200 mm nominal is 390 × 190 mm, and with 10 mm joints fills 0.4 × 0.2 = 0.08 m² — 12.5 blocks per m². A US 8 × 16 in CMU is 7⅝ × 15⅝ in and fills 8/9 ft², 1.125 units per ft². The wall thickness is the actual block width.
Wall area = the walls − the openings. Blocks to buy = area × blocks per m² × (1 + wastage), rounded up; CMHA suggests 5 % for waste and breakage.
Mortar, cement and sand (IS blocks and AAC)
Wet mortar is the joint space: the wall volume minus the volume of the blocks. IS 2572 lays hollow blocks with mortar over the face shells and webs (full bedding) — face-shell bedding is allowed only for lightly loaded panel walls — so for hollow blocks only the solid share of the bed face takes mortar. IS 2185-1 defines a hollow block as 50–75 % solid; the calculator starts at 75 % (the most mortar a hollow block can take), and you can enter your block's figure. Solid and AAC blocks are bedded in full.
Loose cement and sand take more room than the mortar they make, so dry volume = wet volume × a dry-volume factor (1.27–1.33 is usual) × (1 + wastage), split in the mix ratio. Cement is converted at 1,440 kg/m³ (IS 875 Part 1) into bags. IS 2572 Table 1 recommends lean, lime-based mortars for unreinforced block masonry and cement–sand 1 : 7–8 where reinforcement is used; IS 6041 suggests 1 : 6 cement–sand for AAC when good lime is not available. Joints are 10 mm thick in both codes.
Thin-bed adhesive for AAC
Polymer-modified block adhesives are laid in joints of a few millimetres, so a wall needs far less material than with mortar — and the amount depends on the product. Enter the coverage printed on your bag, either as m² of wall per bag or as m³ of blockwork per bag; the calculator divides your wall area or volume by it and rounds up. The joint space it shows (wall volume − blocks) lets you compare with the product's own consumption figure.
US CMU: mortar and grout (CMHA TEK 4-2A)
For conventional 8 × 16 in CMU laid with face-shell mortar bedding, one batch of mortar lays about 62 units of Type N (1 ft³ portland cement, 1 ft³ lime, 6 ft³ sand), 46 of Type S (1 : ½ : 4½), 38 of Type M (1 : ¼ : 3¾) or 93 of Type O (1 : 2 : 9). Eight 70 lb bags of masonry cement with 1 ton of sand lay about 240 units, and one 80 lb bag of preblended mortar about 16. These figures include nominal waste. A bag of portland cement is 1 ft³ (94 lb), a bag of hydrated lime 1¼ ft³ (50 lb), and 1 ton of damp loose sand about 25 ft³.
Grout per 100 ft² of wall with every cell filled: 25.6 ft³ for 6 in, 36.1 for 8 in, 47.0 for 10 in, 58.9 for 12 in and 74.5 for 14 in units; with cells grouted at 16, 24 or 48 in on centre, about half, a third or a sixth of that. Values include 3 % waste and assume two-core units; 4 in units are not grouted.
Standard sizes
- IS 2185 (Part 1): nominal length 400, 500 or 600 mm, height 200 or 100 mm, width 50, 75, 100, 150, 200, 250 or 300 mm; actual length and height are 10 mm less. Hollow blocks are 50–75 % solid, solid blocks at least 75 %.
- IS 2185 (Part 3) AAC: nominal length 400, 500 or 600 mm, height 200, 250 or 300 mm, width 100, 150, 200 or 250 mm; actual sizes are 10 mm less, or 6 mm where finer joints are specified. Many suppliers quote the actual size of the block — choose actual for those.
- US CMU: nominal widths 4 to 14 in with an 8 × 16 in face; actual dimensions are ⅜ in less to suit ⅜ in joints.
Sources
- IS 2185 (Part 1):2005, Concrete masonry units — Hollow and solid concrete blocks: cl. 3.7, 3.10, 4.2 — archive.org
- IS 2185 (Part 3):1984, Autoclaved cellular (aerated) concrete blocks: cl. 3.2 — archive.org
- IS 2572:2005, Construction of hollow and solid concrete block masonry: cl. 6.9, 6.10, 11.1 and Table 1 — archive.org
- IS 6041:1985, Construction of autoclaved cellular concrete block masonry: cl. 3.9 and 7.1 — archive.org
- CMHA (Concrete Masonry & Hardscapes Association), TEK 4-2A, Estimating Concrete Masonry Materials, Tables 1–3
- IS 875 (Part 1):1987, Table 1 — cement 1,440 kg/m³ — archive.org
Limitations
- Corners, piers, lintels, bond beams and half blocks at openings change the count; on a wall with many returns, add more wastage or count those units separately.
- Mortar depends on the block's shell and web pattern and on how fully the joints are filled. For hollow blocks the bedded share is an estimate — measure your block for a better figure.
- Adhesive bags come only from the coverage you enter; products differ widely.
- The CMU tables are rules of thumb for conventional face-shell-bedded walls; grout for bond beams and lintels is extra.
- Wall thickness, block strength and reinforcement for load-bearing walls are design decisions for your engineer (IS 1905 in India).
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Frequently asked questions
How many concrete blocks are in 1 m² of wall?
For a 400 × 200 mm (nominal) block laid with 10 mm joints, 1 ÷ (0.4 × 0.2) = 12.5 blocks per m², whatever the width. A 500 × 200 mm block gives 10 per m² and a 600 × 200 mm block 8.33. Add about 5 % for breakage and cutting.
How many AAC blocks are in 1 m²?
With 600 × 200 mm blocks (actual size) and 3 mm thin-bed joints, 1 ÷ (0.603 × 0.203) = 8.17 per m²; with 10 mm mortar joints, 1 ÷ (0.61 × 0.21) = 7.81 per m². For a 150 mm thick wall that is about 54.5 blocks per m³ of blockwork with thin joints.
How much cement do I need for a block wall?
For 100 m² of 200 mm hollow blocks (400 × 200 mm nominal, 10 mm joints) with 75 % of the bed face mortared, the wet mortar is about 1.11 m³. With a 1 : 6 mix, a 1.33 dry-volume factor and 15 % wastage, that is about 348 kg — 7 bags of 50 kg.
How many CMU blocks per square foot?
A standard 8 × 16 in CMU covers 8/9 ft², so 1.125 blocks per ft² or 112.5 per 100 ft². CMHA rounds this to 119 per 100 ft² with 5 % waste.
How much grout does an 8 inch block wall need?
With every cell grouted, about 36.1 ft³ per 100 ft² of wall (1.34 yd³), including 3 % waste (CMHA TEK 4-2A Table 3). Grouting cells at 48 in on centre needs about 6.1 ft³ per 100 ft².
Is the block size nominal or actual?
IS 2185 and US CMU sizes are nominal: they include one 10 mm (or ⅜ in) joint, so a "400 × 200" block is really 390 × 190 mm. Many AAC suppliers quote the actual size instead, such as 600 × 200 × 150 mm. Choose the basis that matches your supplier's figures — the count depends on it.