Cinder Block Calculator
Blocks, mortar and cost for any CMU wall, including waste allowance.
Enter your values
ⓘ Live results
- Blocks needed
- 189 blocks
- Net wall area
- 160 sq ft
- Courses (8 in high)
- 12
- Mortar
- 6 × 80 lb bags
- Masonry sand
- 0.17 tons
- Block cost
- $444.15
About one bag per 33 blocks for standard 3/8 in joints.
Working
- 1Wall area = 20 × 8 = 160 sq ft
- 2Blocks = 160 ÷ 0.889 = 180
- 3Add 5% waste → 189 blocks
Quick answer
A standard 8×8×16 in cinder block with mortar joints covers 0.889 sq ft, so a wall needs about 1.125 blocks per square foot. Multiply wall length × height, then by 1.125, then add 5–10% for waste.
Blocks = wall area ÷ block face area × (1 + waste)
How to use the Cinder Block Calculator
- 1Measure wall length and height.
- 2Subtract doors and windows.
- 3Choose the block size and add a waste allowance.
Worked example
Using the values the calculator loads with:
Inputs
- Wall length20 ft
- Wall height8 ft
- Block size8" × 8" × 16" standard CMU
- Openings to subtract0 sq ft
- Waste allowance5 %
- Price per block2.35 $
Results
- Blocks needed189 blocks
- Net wall area160 sq ft
- Courses (8 in high)12
- Mortar6 × 80 lb bags
- Masonry sand0.17 tons
- Block cost$444.15
- Wall area = 20 × 8 = 160 sq ft
- Blocks = 160 ÷ 0.889 = 180
- Add 5% waste → 189 blocks
Frequently asked questions
How many cinder blocks per square foot?
About 1.125 standard 8×8×16 blocks per square foot of wall, because each block with its mortar joint covers 0.889 sq ft.
How much mortar do I need for cinder block?
Roughly one 80 lb bag of mortar mix per 33 blocks with standard 3/8 inch joints, plus masonry sand if you are mixing from Type S.
How many blocks for a 20 ft × 8 ft wall?
160 sq ft ÷ 0.889 = 180 blocks, or about 189 with a 5% waste allowance.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.