Estimate exactly how many concrete blocks (CMUs), bags of mortar and dollars you need for any wall — pick a preset US block size or enter custom dimensions, in metric or imperial.
Created by
Daniel Whitman
Reviewed by
Hannah Brooks
Enter your wall height and width, choose a block size, then add a price per block and mortar bag to see total cost. The calculator follows the standard masonry rule of three bags of mortar per 100 blocks, plus an adjustable waste percentage for cuts and breakage.
Concrete block calculator
Wall dimensions
Block size
Cost & waste
Results
Wall area
500 ft² · 46.45 m²
Single block face area
128 in² · 825.8 cm²
Blocks needed (no waste)
563
Blocks with 10% waste
619
Mortar bags (≈ 1 / 33.3 blocks)
19
Estimated cost
Blocks$928.50
Mortar$152.00
Total$1,080.50
Estimates only. Actual material requirements vary with wall thickness, joint size, openings (doors / windows), block voids and mortar type. Always confirm with your supplier before ordering.
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How the concrete block calculator works
The math behind a block-wall estimate is straightforward. The calculator above just automates the unit conversions and rounding so you can compare wall sizes and block types quickly.
Wall area = wall height × wall width.
Single block face area = block height × block width.
Blocks needed = wall area ÷ block face area, rounded up.
Mortar bags = blocks ÷ 33.3 (≈ 3 standard bags per 100 blocks).
Total cost = (blocks × price per block) + (mortar bags × price per bag).
For irregular walls with windows, doors or step-downs, calculate the gross wall area first, then subtract the openings before dividing by the block face area. For curved or stepped retaining walls, sum the area of each straight segment.
Concrete block reference tables
Block sizes, mortar coverage and quick wall-by-wall block estimates so you can sanity-check the calculator before you order materials.
US standard CMU face areas
Block sizes
Block
Face area (in²)
Face area (m²)
Per m² of wall
16" × 8" (standard CMU)
128
0.083
12.1
12" × 8"
96
0.062
16.1
8" × 8"
64
0.041
24.2
16" × 4" (cap / half)
64
0.041
24.2
12" × 4"
48
0.031
32.3
8" × 4"
32
0.021
48.4
Mortar bags per number of blocks
Mortar
Blocks
Standard bags (~80 lb)
50
2
100
3
250
8
500
15
1,000
30
2,000
60
Blocks needed for common walls (16″ × 8″)
Estimates
Wall
Area (ft²)
Blocks
8 ft × 10 ft (small shed wall)
80
90
10 ft × 20 ft (garage side)
200
225
10 ft × 50 ft (long boundary)
500
563
8 ft × 100 ft (yard fence)
800
900
12 ft × 60 ft (warehouse bay)
720
810
Worked example: a 10 ft × 50 ft block wall
Suppose you're building a 10 ft tall, 50 ft long boundary wall using standard 16″ × 8″ concrete blocks at $1.50 per block, with mortar bags at $8.00:
›How do I calculate how many concrete blocks I need?
Multiply the wall height by the wall width to get the wall area, then divide by the face area of one block (block height × block width). For a 10 ft × 50 ft wall using a standard 16″ × 8″ block, that's 500 ft² ÷ 0.889 ft² ≈ 563 blocks. Always round up to the nearest whole block.
›What are the most common cinder block sizes?
In the US, standard concrete masonry unit (CMU) face sizes are 16″ × 8″, 12″ × 8″ and 8″ × 8″ for full-height blocks, and 16″ × 4″, 12″ × 4″ and 8″ × 4″ for half-height (cap) blocks. Nominal sizes include a 3⁄8″ mortar joint, so an actual 16″ × 8″ block is really about 15 5⁄8″ × 7 5⁄8″.
›How many bags of mortar do I need per 100 blocks?
A common rule of thumb is three standard 80 lb (≈ 36 kg) bags of mortar per 100 standard 16″ × 8″ concrete blocks. That works out to roughly one bag per 33 blocks. For type-N or pre-mixed mortar, always follow the manufacturer's coverage rate on the bag.
›How much waste should I add when ordering concrete blocks?
Add at least 5–10% extra blocks for cuts, breakage and future repairs. The calculator above includes a waste percentage field — bump it to 15% if the wall has many corners, openings or curves.
›Is this concrete block calculator free?
Yes. Every calculator on Calculator Friendly is free, mobile-friendly and works without an account. If you need a different construction calculator, request it on our help page.
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Hannah Brooks