Cmu Block Calculator

Leave the dimensions blank if you already know the net wall area.
Subtracted from the gross wall area.
Use this when you already have the area to be built.
In the same area unit as the wall. Leave at 0 to use the selected standard unit.
The standard joint for both concrete masonry and brick is 3/8 in.
Leave at 0 unless you are filling the cores. Core sizes vary by producer - take them from the unit’s data sheet.
Units to buy
189
Concrete Block & Brick Calculator
Blocks to buy
189
Bricks to buy
189
Net wall area used
160.000
Face area of one unit with joints
0.88889
Units per area unit of wall
1.1250
Units before the waste allowance
180
Mortar in the joints
7.389 ft3
Mortar in the joints
0.2092 m3
Cost of the units
472.50 USD
Worked out from ASTM C90, Standard Specification for Loadbearing Concrete Masonry Units and 2 other sources.
Mortar is the theoretical joint volume for full bedding. Hollow concrete masonry is normally face-shell bedded, which uses less, and site waste typically adds 10-25%.
This is a materials take-off, not a structural design. Wall thickness, reinforcement, grouting and lintels over openings must come from a design by a licensed engineer or from the prescriptive provisions of the code adopted where you build (e.g. TMS 402/602, IRC Chapter 6).

How this is worked out

5 steps
  1. Wall: 20 ft x 8 ft = 160 ft2 gross = 160 ft2 net.
  2. 8 in concrete block (cinder block), nominal 8x8x16: nominal face 8 in x 16 in = 128 sq in = 0.888889 ft2, i.e. 1.125 units per ft2.
  3. With 5% waste: 160 x 1.05 = 168 ft2.
  4. Units = ceil(168 / 0.888889) = 189.
  5. Mortar: module 128 sq in less the specified face 7.625 x 15.625 in, bedded 7.625 in deep, over 189 units = 7.3886 cu ft.

Results are general information, not financial, tax, legal, medical or engineering advice.