Cinder Block Wall Calculator
Count the 8×8×16 blocks for a wall plus the mortar bags and vertical rebar it needs, from the wall length and height.
How it works
blocks = wall area × 1.125 (8×8×16 face with joint) · mortar bags = blocks ÷ 12 · vertical bars = floor(length ÷ spacing) + 1 · rebar length = bars × height
A standard 8×8×16 concrete block covers about 0.89 square feet of wall face including its mortar joint, so roughly 1.125 blocks fill each square foot. An 80-pound bag of mortar mix lays around a dozen blocks. Vertical rebar sits in the grout-filled cores at code spacing — often every 32 to 48 inches — with the cells then filled solid; horizontal bars in bond-beam courses are a separate add. Confirm reinforcement against your local code and the wall’s height and retained load.
Worked example
A 20 × 8 ft wall is 160 sq ft. Blocks: 160 × 1.125 = 180. Mortar: 180 ÷ 12 = 15 bags. Rebar at 4 ft on center: floor(20 ÷ 4) + 1 = 6 bars × 8 ft = 48 ft of vertical steel.
Frequently asked questions
How many blocks are in a square foot of wall?
For the common 8×8×16 block, about 1.125 blocks per square foot once you include the 3/8-inch mortar joints. Multiply your wall’s square footage by 1.125 and round up.
How much rebar does a block wall need?
It depends on height, wind and whether the wall retains soil, but codes commonly call for #4 vertical bars every 32–48 inches in grouted cells, plus horizontal bars in bond beams. Freestanding and retaining walls have stricter rules — check locally.
Do I have to grout every core?
No. Only the cells with rebar are typically filled with grout, unless the design calls for a fully grouted wall. Grouting the reinforced cells locks the steel to the block so they act together.
Related calculators
Estimates only — add for waste and confirm against local building codes and supplier specs.