Primary material
189 blocks
Concrete block (CMU)
Use the calculated block count as a buying starting point, then confirm the exact block size, weight, and pallet quantity with the store.
Concrete block calculator
Concrete block calculator for CMU walls.
Enter wall length, height, and openings to estimate how many 8 x 8 x 16 in blocks and bags of mortar you need, plus rough material cost. Uses about 1.125 blocks per square foot.
20 x 8 ft wall
189 blocks
~6 bags mortar
Coverage
1.125 /sq ft
Standard 8x8x16 CMU
Mortar
~3 / 100
bags per 100 blocks
Quick block answers
Common block walls
20 ft x 4 ft garden wall
80 sq ft
95 blocks
about 3 bags of mortar
32 ft x 8 ft foundation
256 sq ft
303 blocks
about 10 bags of mortar
10 ft x 8 ft shed wall
80 sq ft
95 blocks
about 3 bags of mortar
Half blocks and corners
Corners, half blocks, bond beams, and cap blocks change the mix of pieces you buy even when the total count is close. Confirm the layout course by course for a tight order.
Shopping list
Block, mortar, and tools
Block and mortar counts update from the calculator. Confirm exact block size, pallet quantity, and mortar coverage with the store before ordering.
Setting material
6 bags
Mortar mix
Mortar use varies with joint size and block type. The estimate assumes about 3 bags per 100 blocks — verify against the bag coverage chart.
Optional reinforcement
Rebar, grout, and ladder wire
Many block walls need vertical rebar, grouted cores, and horizontal joint reinforcement. Plan these from your wall design, not the block count alone.
Install tools
Trowel, jointer, line, and level
Block work needs a mason trowel, jointer, mason line and blocks, a level, and mixing tools or a mixer for larger walls.
Formula shown
How the block estimate works
1. Net wall area
length ft x height ft - openings sq ft
2. Block count
blocks = ceil(net area x 1.125 x (1 + waste))
3. Mortar
mortar bags = ceil(blocks / 100 x 3)
What this does not include
Vertical rebar, grout-filled cores, horizontal joint reinforcement, footings, lintels, and cap blocks depend on the wall design and local code. Estimate those separately. The mortar figure assumes standard 3/8 inch joints.
Sources
- CMU block coverage reference — 8x8x16 block coverage (~1.125 block per sq ft)
- Quikrete mortar references — mortar mix coverage and bag guidance
- ConcreteNetwork price guide — block wall material and installed cost context
Reviewed for estimating accuracy
Last updated: June 25, 2026
Estimate only.
This calculator is not a quote. Verify product yield, price, delivery minimums, and local conditions with your supplier or contractor before buying materials.
FAQ
Concrete block questions
Block counts, blocks per square foot, mortar per block, openings, and what the estimate leaves out.
How many concrete blocks do I need for a wall? + -
Multiply wall length by height for the area, subtract any openings, then multiply by about 1.125 standard 8x8x16 blocks per square foot and add waste. A 20 ft by 8 ft wall (160 sq ft) needs roughly 189 blocks with 5% waste.
How many concrete blocks are in a square foot? + -
A standard 8 in by 8 in by 16 in CMU covers about 0.889 square feet of wall with its mortar joint, so you need about 1.125 blocks per square foot of wall area.
How much mortar do I need for concrete block? + -
A common trade rule is about 3 bags of mortar mix per 100 blocks at 3/8 inch joints. The 189-block example above works out to about 6 bags. Verify against your mortar bag coverage chart and joint size.
Do I subtract doors and windows? + -
Yes. Enter the total opening area in square feet and the calculator removes it from the wall area before counting blocks. For large openings, also plan lintels or bond beams separately.
Does this include rebar, grout, or footings? + -
No. This estimates block and mortar quantities only. Vertical rebar, grouted cores, horizontal joint reinforcement, footings, and caps depend on your wall design and local code and should be estimated separately.