Concrete Block Calculator
Estimate blocks needed, mortar bags, and total cost for any CMU (concrete masonry unit) wall project. Standard 8x8x16 blocks cover 1.125 sq ft each.
Concrete block sizes reference
| Block size | Face area | Blocks/100 sq ft | Typical use |
|---|---|---|---|
| 8 × 8 × 16 (most common) | 1.125 sq ft | ~113 blocks | Foundation, garage, retaining walls |
| 4 × 8 × 16 | 1.125 sq ft | ~113 blocks | Partition walls, half-thickness |
| 6 × 8 × 16 | 1.125 sq ft | ~113 blocks | Medium walls |
| 12 × 8 × 16 | 1.125 sq ft | ~113 blocks | Large foundation walls |
| Half-block (8 × 4 × 16) | 0.444 sq ft | ~225 blocks | Corner & end finishes |
FAQs
How do I calculate concrete blocks needed?
Formula: Number of blocks = (Wall length × Wall height) / (Block face area). Standard 8x8x16 CMU has face area of 8" × 16" = 1.125 sq ft. For a 30 ft × 8 ft wall: (30 × 8) ÷ 1.125 = 213 blocks. Add 10% for waste/breakage.
How many concrete blocks per square foot?
Standard 8x8x16 CMU: 1.125 blocks per square foot of wall. 4x8x16 CMU: 1.125 blocks per square foot. 6x8x16 CMU: 1.125 blocks per square foot. (All standard blocks have same 8" × 16" face dimensions; thickness differs.) For 100 sq ft of wall, plan on ~125 blocks (including 10% waste).
How much mortar do I need for concrete blocks?
Approximately 1 bag of premix mortar (80 lb) per 25-30 blocks. For a 200-block wall: 7-8 bags of mortar. Premium estimate: 1 bag per 20 blocks if you're learning or working in difficult conditions. Always order 10-15% extra.
What's the cost of concrete blocks?
Standard 8x8x16 CMU costs $1.50-$3.50 per block in 2026, depending on region and quantity. Mortar adds about $4-$8 per bag. For a 200-block wall: $300-$700 in materials + labor of $4-$8 per block installed = total $500-$2,000+ depending on complexity.
What sizes of concrete blocks are available?
Common CMU sizes (nominal dimensions, actual is 3/8" smaller for mortar joint): 8x8x16 (most common, full-size load-bearing wall), 4x8x16 (partition walls), 6x8x16 (medium walls), 12x8x16 (large foundation walls), 8x4x16 (half-height). All share the 16-inch length and most share 8-inch height — the depth varies for load-bearing requirements.
How tall can a concrete block wall be?
Without reinforcement (rebar + mortar fill): max 4 feet for retaining walls, 8 feet for non-retaining. With proper engineering (rebar every 32-48" vertical, bond beams every 8-10 ft), CMU walls can reach 20+ ft. Always consult an engineer for retaining walls over 4 feet or load-bearing walls over 10 feet.