How the block calculator works
Blocks = Wall area × 1.125 × (1 + waste)
Mortar = Blocks ÷ blocks per bag
A standard 8×8×16 block is 7⅝ × 7⅝ × 15⅝ inches; with a 3/8-inch mortar joint it covers exactly 8 × 16 inches, or 0.889 sq ft. That works out to 1.125 blocks per square foot. Each course adds 8 inches of height.
Mortar
Quikrete rates an 80 lb bag of its Mortar Mix at up to 13 standard 8×8×16 blocks.
Planning notes
- Plan wall lengths in multiples of 8 inches to minimize cuts.
- Corners and ends need half blocks or corner blocks; order a few extra.
- Foundations and retaining walls need footings, rebar and grout per local code — talk to your building department.
Sources
Frequently asked questions
How many cinder blocks per square foot?
1.125 standard 8×8×16 blocks per square foot of wall.
How many blocks does a bag of mortar lay?
About 13 standard blocks per 80 lb bag of Quikrete Mortar Mix.
How many blocks for a 4 ft high wall?
Six courses (rows) of 8-inch blocks, with 0.75 blocks per foot of length in each course.