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Concrete, Masonry & Stone

Concrete Block Calculator

Block, mortar, rebar and fill for a wall, from its dimensions and block size.

Your measurements

Openings are deducted before the block count.

Wall
Total area of doors, windows and vents.
Block and reinforcement
A standard block covers 8/9 of a square foot with its mortar joint, so 1.125 block per ft².

Your result

Sample values

284

Blocks

240

Wall area, ft²

11

Bags of mortar

0.61

Cubic yards of fill

Standard 8 in block, rebar at 48 in, reinforced cores filled, 5% waste.

What to order

Item Quantity
8 × 8 × 16 block 284
Mortar, 80 lb bags 11 bags
#4 rebar, 20 ft lengths 12 lengths
Grout for cores 1.1 yd³
Masonry sand 0.6 tons

How to use this calculator

Enter the finished wall length and height and deduct any openings. Block walls are usually designed to land on whole courses and whole block, so if you can adjust the height to a multiple of 8 in you will save a great deal of cutting.

Set the rebar spacing from your drawings or local code rather than by feel. Vertical bar spacing drives both the steel order and the grout volume, because only the cores containing bar normally get filled.

Formula

Net area = (Length × Height) − Openings

Blocks = Net area × 1.125 × (1 + Waste)

Courses = Height ÷ 8 in

1.125
standard block per square foot, including mortar joints
Courses
a standard block plus joint is 8 in high

Grout volume counts only the cores that contain reinforcement unless all cores are filled.

Worked example

A 40 ft by 6 ft garden wall in standard 8 in block, no openings, rebar at 48 in, 5% waste.

  1. 40 ft × 6 ft = 240 ft² of wall
  2. 240 ft² × 1.125 block per ft² = 270 block
  3. 270 × 1.05 = 284 block with waste
  4. 6 ft ÷ 8 in = 9 courses
  5. 40 ft ÷ 48 in = 10 reinforced cores, plus ends
  6. 284 block ÷ 27 block per bag = 11 bags of mortar

284 block, 11 bags of mortar, 12 lengths of #4 rebar

Understanding your results

The 1.125 block per square foot figure already includes the mortar joint, which is why it is not simply the face area of a block. It holds for any wall built in standard 8 × 16 units regardless of thickness — a 12 in block covers the same face area as an 8 in one, it is just deeper.

Grout is the number most likely to surprise. Filling every core in this wall rather than only the reinforced ones would take roughly four times the concrete, so it is worth confirming what the design actually requires before ordering a truck.

Questions

About this calculator

Ask something else

Typically 90 standard 8 in block, though it varies by manufacturer between about 80 and 108. Ordering by the pallet is usually cheaper and blocks damaged in transit are easier to claim, so round up to a full pallet if you are within a few units.

Almost always, and your local code will say how much. Even a low freestanding wall takes wind load and ground movement, and unreinforced block has very little resistance to bending. Anything retaining soil needs an engineered design rather than a rule of thumb.

Only if the design says so. Full grouting adds a great deal of weight, cost and concrete, and is normally reserved for retaining walls, tall walls and structures carrying significant load. Partial grouting of reinforced cores is the common approach for ordinary walls.

Wider than the wall and below the frost line, with its own reinforcement and dowels left projecting to tie into the block cores. Footing size depends on soil and wall height, so it comes from the drawings or the code, not from this calculator.

Keep going

All Concrete, Masonry & Stone tools
Estimates, not specifications. Results are based on the values you enter and on typical material properties. Densities, coverage rates and product sizes vary between suppliers, so confirm quantities against your supplier's data before ordering. Structural work must be signed off by a qualified professional and meet your local building code.