Concrete Block, Mortar & Fill Calculator

Blocks = wall area ÷ the face of one block with its mortar joint (16 × 8 in), plus extra: a wall 20 ft long and 4 ft high is 80 sq ft, or 90 blocks, 99 with 10% extra.

Your measurements

Example

Use the unit shown for each box, or type another one: 12 ft 6 in, 150 in, 3.8 m and 600 mm all work, as do the marks on a tape measure.

Wall 1

Wall length (ft) Wall height (ft) Openings (sq ft)

Extra for cuts (%)

Details Package sizes, prices and materials

Actual block length Actual block height Mortar joint Blocks laid per mortar bag Your price per block ($) Block cores to fill from design Fill volume per block from label (cu ft)

Example: replace these measurements

Your material list

99 concrete blocks

80 sq ft measured

Your measured layout

Wall elevation before subtracting openings. Block courses are schematic, not a bond or structural design.

Your shopping list

99 concrete blocks

Quantities and package details

Wall area after openings: 80 sq ft
Block positions before extra: 90
Mortar bags: Enter product yield
Core fill from supplied design: Enter filled cores and volume per unit

The calculation

80 ÷ ((15.63 + 0.38) × (7.63 + 0.38) ÷ 144) = 90 block positions
90 × (1 + 10/100), rounded up = 99 blocks

Common questions

How many concrete blocks per square foot?

About 1.125 for standard blocks. A block of 15 5/8 by 7 5/8 inches with a 3/8-inch mortar joint takes up 16 by 8 inches, which is 128 square inches, and a square foot is 144 square inches.

How much mortar do I need?

It depends on the mortar and how the blocks are laid. Enter the blocks per bag from the mortar maker’s guidance and the calculator counts the bags.

Do I subtract doors and windows?

Yes, as square feet. Corners, ends and openings often need special blocks, which are ordered separately from ordinary blocks.

How to plan the quantity

Use actual face dimensions plus one mortar joint to get the repeating block position. The calculation divides net wall area by that position area, then adds your chosen allowance.

Corners, ends, bond beams and openings may need special units. Separate those from ordinary stretchers on the supplier order.

Mortar yield depends on the block and how it is laid. Enter blocks per bag from the selected mortar guidance; otherwise mortar stays unpriced and uncounted.

Before you order

Area rounding does not produce a running-bond cut schedule or a structural design.
Footings, reinforcement, grout-filled cores, lintels and wall stability need a design; they are not mortar-bag allowances.

Before ordering, read the guide: How much concrete do I need? Yards, bags and when to order a truck. Or choose another calculator.