Cinder Block Calculator
Blocks, mortar and cost for any CMU wall, including waste allowance.
Enter your values
Enter the wall length in ft.
Enter the wall height in ft.
Choose one of: 8" × 8" × 16" standard CMU, 4" × 8" × 16" half-height, 8" × 12" × 16" tall block.
Enter the openings to subtract in sq ft.
Enter the waste allowance in %.
Enter the price per block in $.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- 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
- $444.15
About one bag per 33 blocks for standard 3/8 in joints.
Working
- 1Wall area = 20 × 8 = 160 sq ft
- 2Blocks = 160 ÷ 0.889 = 180
- 3Add 5% waste → 189 blocks
Quick answer
A standard 8×8×16 in cinder block with mortar joints covers 0.889 sq ft, so a wall needs about 1.125 blocks per square foot. Multiply wall length × height, then by 1.125, then add 5–10% for waste.
Blocks = wall area ÷ block face area × (1 + waste)
At a glance
| What it does | Blocks, mortar and cost for any CMU wall, including waste allowance. |
|---|---|
| Category | Home & DIY |
| Inputs needed | Wall length, Wall height, Block size, Openings to subtract, Waste allowance, Price per block |
| Main output | Blocks needed |
| Formula | Blocks = wall area ÷ block face area × (1 + waste) |
| Cost | Free — no sign-up, no download |
How to use the Cinder Block Calculator
- 1Measure wall length and height.
- 2Subtract doors and windows.
- 3Choose the block size and add a waste allowance.
Inputs explained
- Wall length(ft)
- Enter the wall length in ft.
- Wall height(ft)
- Enter the wall height in ft.
- Block size
- Choose one of: 8" × 8" × 16" standard CMU, 4" × 8" × 16" half-height, 8" × 12" × 16" tall block.
- Openings to subtract(sq ft)
- Enter the openings to subtract in sq ft.
- Waste allowance(%)
- Enter the waste allowance in %.
- Price per block($)
- Enter the price per block in $.
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.
What do I need to enter into the Cinder Block Calculator?
Just 6 values: wall length, wall height, block size, openings to subtract, waste allowance, price per block. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Cinder Block Calculator work out the 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. It applies the formula Blocks = wall area ÷ block face area × (1 + waste) and shows the working so you can check each step by hand.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.