Concrete Block (Cinder Block) Calculator
Enter the wall length and height and subtract any doors or windows. You'll get the number of 8 × 8 × 16 blocks, 80 lb bags of mortar, and grout if you fill some or all of the cells.
- Tested formulas
- Feet or metric
- Printable shopping list
2 What to buy
Updates as you type| Wall area (less openings) | 160 sq ft |
|---|---|
| Blocks before extra | 180 |
| Full courses × blocks per course | about 6 × 30, before openings |
| Mortar | 15 bags of QUIKRETE Mortar Mix (Type N) or Mason Mix (Type S), 80 lb |
Block walls that hold back soil or carry a load need steel reinforcing bars in grouted cells and a proper footing. The building code and your local building department set the spacing, so get a permit before you build one.
Shopping list
Quick answer
Concrete blocks = wall area in sq ft × 1.125. A 40 × 4 ft wall is 160 sq ft, which takes 180 blocks (8 × 8 × 16 in) or 189 with 5% extra, plus about 15 bags of 80 lb mortar mix.
Blocks and mortar for common wall sizes
| Wall area | Blocks | Mortar bags |
|---|---|---|
| 50 sq ft | 60 | 5 |
| 100 sq ft | 119 | 10 |
| 160 sq ft | 189 | 15 |
| 250 sq ft | 296 | 23 |
| 400 sq ft | 473 | 37 |
| 600 sq ft | 709 | 55 |
| 1,000 sq ft | 1,182 | 91 |
8 × 8 × 16 in blocks with 5% extra; mortar at 13 blocks per 80 lb bag. Use the calculator above for your exact size.
How many blocks per square foot
A standard block is 8 × 8 × 16 inches nominal. It actually measures 7⅝ × 7⅝ × 15⅝ inches, and the ⅜ inch mortar joint makes up the rest. So each block covers 8 × 16 = 128 square inches of wall, which works out to 1.125 blocks per square foot.
Worked example: a 40 ft wall, 4 ft high
- 40 × 4 = 160 sq ft of wall.
- 160 × 1.125 = 180 blocks, plus 5% = 189 blocks.
- That's 6 courses of 30 blocks.
- QUIKRETE rates its 80 lb Mortar Mix at up to 13 blocks per bag: 15 bags.
Mortar: why the estimates differ
CMHA (formerly NCMA) estimates about 16 blocks per 80 lb bag of preblended mortar. QUIKRETE's data sheet says up to 13 for its Mortar Mix, and Sakrete says 12 for its Type S. Real yield depends on joint width and how much you drop, so the bag maker's figure is the safer one to buy by. Leftover bags keep if they stay dry.
Grout for filled cells
Walls with steel reinforcing bars get grout poured into the cells that hold the bars. For an 8 inch wall, CMHA TEK 04-02A gives these amounts per 100 sq ft of wall:
| Grouted cells | Grout per 100 sq ft |
|---|---|
| Every 16" | 18.1 cu ft |
| Every 24" | 12.1 cu ft |
| Every 32" | 9.1 cu ft |
| Every 48" | 6.1 cu ft |
| All cells | 36.1 cu ft |
The bar size and spacing come from your plans or the local building department, not from this calculator.
Before you build
- Block walls sit on a concrete footing, which goes below the frost line in cold climates. Footing size depends on the wall, the soil and local code.
- Retaining walls and taller walls usually need steel bars and grout to code. Check with your local building department, which often requires a permit.
- Plan the wall length in 8 inch steps where you can. You'll cut fewer blocks.
Frequently asked questions
How many concrete blocks are in a square foot?
1.125 standard 8 × 8 × 16 blocks, because each one covers 8 × 16 inches of wall including the mortar joint. That's 112.5 blocks per 100 sq ft before any extra.
How many blocks can I lay with one bag of mortar?
About 12 to 16 blocks per 80 lb bag. QUIKRETE says up to 13 for its Mortar Mix, Sakrete says 12 for Type S, and CMHA estimates 16 for preblended mortar.
What size is an 8 × 8 × 16 block really?
7⅝ × 7⅝ × 15⅝ inches. The nominal size includes a ⅜ inch mortar joint.
Do I need to fill concrete blocks with concrete?
Only the cells that hold steel bars, or all of them if your plans call for a solid grouted wall. Use grout (a fluid concrete mix) rather than regular concrete, and follow the bar spacing in your plans or local code.
Last reviewed 2026-10-23. See how we calculate for our sources and assumptions.