Why does block count use nominal face dimensions?
Nominal block dimensions (e.g. 8x16 in) already include the mortar joint allowance -- a 16 in block plus its joint occupies 16 in of wall -- which is the standard masonry takeoff convention.
CMU Block Wall Calculator
Block count and mortar volume for a concrete masonry unit (CMU) wall.
You'll need — CMU blocks and — cu ft of mortar for this wall.
Wall dimensions
Length and height of the wall to be built. Type a plain number in feet, or tape-measure notation like 10' 6-3/4".
Openings
Doors, windows and other holes in the wall face. Block is bought by face area, so anything not built has to come off it. Leave this empty only if the wall really is solid.
Block and joint (optional)
Standard CMU is 8x16 in nominal face, 8 in deep, with a 3/8 in mortar joint. Adjust only if you're using a non-standard block.
You'll need — CMU blocks and — cu ft of mortar for this wall.
You'll need
CMU block wall estimate
Warnings
- ERROR Wall length and height must both be greater than zero.
Detail values
- Gross wall area
- — sq ft
- Openings deducted
- — sq ft
- Wall area to build
- — sq ft
Assumptions
- Block size: 8 in x 16 in nominal face, 8 in deep (8x16x8 is standard CMU)
- Joint thickness: 0.375 in (3/8 in is standard masonry joint)
- Mortar volume: Estimated -- a per-block bed-and-head joint allowance worked out from the block and joint dimensions above, NOT a published mortar yield. Verify against your mix yield and block coring before ordering.
- Openings: None entered -- the full wall face is counted as block
Included: CMU blocks, mortar, waste allowance, deduction for the openings entered.
Not included: labor, delivery, permits, disposal, compaction (enter your intended post-compaction depth/volume — this estimate does not account for compaction itself).
Formula details
- Wall area: wallLength x wallHeight
- Block count: ceil((wallArea / blockFaceArea) x (1 + waste))
Nominal block face dimensions already include the mortar joint allowance -- standard masonry takeoff convention.
- Mortar volume (approximate): blockCountBeforeWaste x jointThickness x (blockLength + blockHeight) x blockDepth / 1728 x (1 + waste)
Rough per-block bed+head joint allowance, not a precise bed/head double-counting model. Sized on the block count BEFORE waste, so the waste percent is applied once -- a block broken in handling is never laid and uses no mortar.
Material List
About this calculator
Enter wall length and height. Standard 8x16 in nominal block and 3/8 in joint are the defaults, both editable.
FAQ
How accurate is the mortar volume?
It's an approximate per-block bed and head joint allowance based on your block size and joint thickness, not a precise bed/head double-counting model -- verify against your mix yield and block coring before ordering.
Disclaimer
Standard block dimensions and mortar joint thickness are industry-universal, not licensed table values. Verify local code and structural requirements before building.