Concrete Block Calculator
Updated Formulas shown
Standard 8×8×16 blocks cover 1.125 per ft². A 40 × 8 ft wall needs 378 blocks with 5% waste and about 30 bags of mortar mix.
Concrete blocks needed
378
incl. 5% waste
- Wall area
- 320 ft²
- Blocks per ft²
- 1.125
- Mortar mix (80 lb bags)
- 30
Nominal sizes include a ⅜ in mortar joint. Add bond-beam and corner blocks per your plans; fill cores with grout where reinforced.
Quick reference
| Wall | Area | Blocks | Mortar bags |
|---|---|---|---|
| 20 × 4 ft | 80 ft² | 95 | 8 |
| 20 × 8 ft | 160 ft² | 189 | 15 |
| 40 × 4 ft | 160 ft² | 189 | 15 |
| 40 × 8 ft | 320 ft² | 378 | 30 |
| 60 × 8 ft | 480 ft² | 567 | 44 |
| 100 × 8 ft | 800 ft² | 945 | 73 |
Related calculators
- Mortar CalculatorHow much mortar do you need? Calculate 80 lb bags of mortar mix for any number of bricks or concrete blocks.
- Brick CalculatorHow many bricks do you need? Calculate bricks and mortar bags for a wall by size and brick type.
- Retaining Wall Block CalculatorCalculate retaining wall blocks from wall length, height and block face size.
- Concrete Footing CalculatorCalculate concrete for continuous wall footings: enter total length, width and depth to get cubic yards and bags.
Frequently asked questions
Is a cinder block the same as a concrete block?
In everyday use, yes. True cinder blocks used coal ash; today's CMUs are concrete with sand and gravel, but the sizes are the same.
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Estimates only. Check quantities with your supplier or contractor before ordering.