Concrete block calculator
Enter the wall's length and height. You get the blocks to order, the courses, the bags of mortar and, if the cores are grouted, the grout in yards and bags.
Inputs
Result
Blocks per square foot
How many units cover a square foot of wall, with standard 3/8 in mortar joints.
| Unit | Face, nominal | Per sq ft | Per 80 lb mortar bag |
|---|---|---|---|
| Concrete block (CMU) | 8 x 16 in | 1.125 | 13 |
| Modular brick | 2-2/3 x 8 in | 6.75 | 37 |
How it is worked out
A standard block is 7-5/8 by 15-5/8 in on its face. With a 3/8 in joint it takes up 8 by 16 in of wall, 128 sq in, so 144 / 128 = 1.125 blocks fill a square foot. A 40 ft wall 4 ft high is six courses of 30 blocks: 180 blocks, 189 with 5% waste, and 14 bags of mortar.
Grout in the cores
Reinforced walls have steel in some cores, and those cores are filled with grout. The cores make up roughly half of a hollow block's volume, which is about 0.26 cu ft for each 8 in block. Solid-grouting every core of that 40 ft wall takes about 47 cu ft, or 1.75 cubic yards. Where only the reinforced cells are grouted, the calculator scales that by the spacing; one core in every six at 48 in on centre.
Percent solid varies by manufacturer and block type, so treat grout as an estimate and add 10% or so for waste and losses into the webs. Masonry grout is a fluid mix to ASTM C476, not ordinary concrete; check what your plans call for.
Questions
How many blocks are in a square foot?
1.125 standard 8 x 16 in concrete blocks, counting the mortar joint. 100 sq ft of wall takes 112.5 blocks before waste.
How many cinder blocks do I need for a 4 ft wall?
Six courses of 8 in block. Each course takes 0.75 blocks per foot of wall, so a 40 ft wall needs 30 a course and 180 in all, plus about 5% for breakage.
How many blocks does a bag of mortar lay?
Quikrete says up to 13 standard 8 x 8 x 16 in blocks per 80 lb bag of Mortar Mix, or up to 37 bricks. That makes about 8 bags per 100 blocks.
How much grout fills a concrete block?
About 0.26 cu ft for each 8 in block if every core is filled, roughly a cubic yard for every 100 blocks. Partly grouted walls need much less.
How many bricks per square foot?
6.75 modular bricks, laid with 3/8 in joints. A 100 sq ft wall takes 675 bricks before waste.