Concrete Block Foundation Calculator
Count concrete blocks and mortar bags for a wall.
Your result
Enter your numbers and press the button. Your result appears here.
A 30×40 foundation has a 140 ft perimeter. Enter the wall height above the footing.
How it works
Blocks = wall area × 144 ÷ (block length × block height, with joints), plus extra. Mortar bags = blocks ÷ blocks per bag.
Example: a 140 ft wall 8 ft high is 1,120 ft², which takes 1,323 blocks with 5% extra and 102 bags of 80 lb mortar.
At a glance
Same settings as the calculator above, changing only the height.
| Height | Wall area | Blocks | Mortar bags |
|---|---|---|---|
| 4 ft | 560 ft² | 662 | 51 |
| 6 ft | 840 ft² | 993 | 77 |
| 8 ft | 1,120 ft² | 1,323 | 102 |
| 10 ft | 1,400 ft² | 1,654 | 128 |
Standard block sizes
| Nominal | Actual | Blocks per 100 ft² of wall |
|---|---|---|
| 4×8×16 | 3⅝ × 7⅝ × 15⅝ in | 112.5 |
| 6×8×16 | 5⅝ × 7⅝ × 15⅝ in | 112.5 |
| 8×8×16 | 7⅝ × 7⅝ × 15⅝ in | 112.5 |
| 12×8×16 | 11⅝ × 7⅝ × 15⅝ in | 112.5 |
Nominal sizes include a ⅜ in mortar joint.
Common questions
How many blocks per square foot?
A standard block with an 8×16 in face covers 1.125 blocks per square foot, or 112.5 blocks per 100 square feet.
How many blocks does a bag of mortar lay?
Quikrete lists its 80 lb Mortar Mix at up to 13 standard 8×8×16 blocks and its 60 lb bag at about 9.
Do I need rebar in a block wall?
Structural and retaining walls usually need vertical rebar and grout-filled cores. Follow your plans and local code.
Sources
- Quikrete 80 lb Mortar Mix (blocks per bag), Lowe's listing: https://www.lowes.com/pd/QUIKRETE-80-lb-Gray-Type-Type-S-Mortar-Mix/5002094147