Block Retaining Wall Calculator
Count concrete blocks and mortar bags for a wall.
Your result
Enter your numbers and press the button. Your result appears here.
Retaining walls over about 4 ft usually need an engineer's design. This counts blocks for the face area only.
How it works
Blocks = wall area × 144 ÷ (block length × block height, with joints), plus extra. Mortar bags = blocks ÷ blocks per bag.
Example: a 30 ft wall 3 ft high is 90 ft², which takes 107 blocks with 5% extra and 9 bags of 80 lb mortar.
At a glance
Same settings as the calculator above, changing only the height.
| Height | Wall area | Blocks | Mortar bags |
|---|---|---|---|
| 2 ft | 60 ft² | 71 | 6 |
| 3 ft | 90 ft² | 107 | 9 |
| 4 ft | 120 ft² | 142 | 11 |
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