Estimate CMU blocks, mortar, and cost for walls and foundations.
Concrete Block Reference
Concrete masonry units (CMU) are versatile building blocks for foundations, walls, and structures. Accurate estimation saves trips to the supplier.
| Block Size | Weight | Per Sq Ft | Common Use |
|---|---|---|---|
| 8×8×16 | 28-35 lbs | 1.125 | Standard walls |
| 12×8×16 | 45-55 lbs | 1.125 | Foundations |
| 4×8×16 | 18-22 lbs | 1.125 | Partition walls |
| 8×4×16 | 15-20 lbs | 2.25 | Half-high veneer |
Frequently Asked Questions
How many concrete blocks do I need for a wall?
Calculate the wall area (length × height) and divide by the face area of one block. A standard 8×8×16 block has a face area of 0.89 sq ft (including mortar joint). Add 5-10% for waste and cuts.
What size are standard concrete blocks?
The most common size is 8×8×16 inches (nominal), which is actually 7.625×7.625×15.625 inches. The difference accounts for the 3/8-inch mortar joint. Half blocks (8×8×8) are used at corners and ends.
How much does a concrete block weigh?
Standard 8×8×16 hollow block: 28-35 lbs. Lightweight block: 22-28 lbs. Solid block: 40-50 lbs. Medium-weight block: 30-38 lbs. Weight varies by aggregate type and manufacturer.
How much mortar do I need for concrete blocks?
About 8.5 bags (80 lb) of mortar mix per 100 standard blocks. One bag of mortar lays approximately 12 blocks. For 500 blocks, you’ll need about 42 bags of 80-pound mortar mix.
How strong is a concrete block wall?
Standard CMU walls have a compressive strength of 1,900 PSI. Filled and reinforced walls are much stronger. Block walls with rebar and grout every 4 feet meet structural requirements for most residential buildings.
Do concrete block walls need rebar?
Building codes typically require vertical rebar every 4 feet and horizontal rebar every 2-4 courses. Fill rebar cells with grout. Bond beam blocks at the top course accept horizontal rebar for added strength.
What is the difference between CMU and cinder block?
CMU (Concrete Masonry Unit) uses portland cement and aggregate. True cinder blocks use coal cinders — they’re lighter but weaker. Modern blocks are CMU, but ‘cinder block’ remains a common colloquial term.
How many courses of block per foot of height?
With standard 8-inch blocks and 3/8-inch mortar joints, you get 1.5 courses per foot of wall height. An 8-foot wall requires 12 courses of block.
Can I build a concrete block wall myself?
Yes, with proper preparation. Key skills: mixing mortar to the right consistency, laying level and plumb courses, tooling mortar joints, and cutting blocks. Start with a small project to build experience.
How long does it take to lay concrete blocks?
An experienced mason lays 400-500 blocks per day. A skilled DIYer can lay 100-200 blocks per day. Larger blocks and simple wall layouts increase productivity.