Concrete Block Calculator
Calculate how many standard 16×8 in concrete blocks you need for any wall — with mortar and a waste allowance.
A 10×10 ft wall (100 sq ft) needs about 113 standard 16×8 in blocks (124 with 10% waste).
How to Use This Concrete Block Calculator
- Enter the wall length and height in feet.
- Set the waste percentage — 10% covers cuts, corners and breakage.
- Read the block count and the mortar estimate.
The Formula
Blocks = wall area ÷ face area per block. A standard block is 16×8 in nominal (0.889 sq ft, including the mortar joint). That works out to about 1.125 blocks per square foot. Mortar: one 80 lb bag of mortar mix lays about 13 standard blocks (Quikrete data sheet).
Blocks = ceil(area ÷ 0.889) 16×8 in block = 128 in² = 0.889 ft² 1.125 blocks per ft² 1 ÷ 0.889 Mortar ≈ 1 bag (80 lb) per 13 blocks Quikrete Mortar Mix data sheet Total = blocks × (1 + waste%) 10% default Worked Example: 10×10 Wall
A 10×10 ft wall: 100 sq ft ÷ 0.889 = 112.5 → 113 blocks. With 10% waste: 110 sq ft ÷ 0.889 = 123.75 → 124 blocks. Mortar: about 9 bags (113 ÷ 13).
Blocks Needed by Wall Size
| Wall size | Area | Blocks (10% waste) | Mortar bags (80 lb) |
|---|---|---|---|
| 8 × 8 ft | 64 sq ft | 80 | 6 |
| 10 × 8 ft | 80 sq ft | 99 | 7 |
| 10 × 10 ft | 100 sq ft | 124 | 9 |
| 20 × 8 ft | 160 sq ft | 198 | 14 |
| 30 × 8 ft | 240 sq ft | 297 | 21 |
Blocks rounded up. Mortar ≈ 1 bag (80 lb) per 13 blocks (Quikrete).
Block Walls: What to Know
Standard concrete blocks (CMU) measure 16×8 in nominal — the real block is slightly smaller and the mortar joint makes up the difference. For structural walls, add vertical rebar and fill cores with concrete; for garden and retaining walls, the blocks are often used dry or with adhesive. Always check local codes for load-bearing walls.
Quick Tips
- Order 10% extra for cuts at corners and around openings.
- Standard blocks lay 12.5 per square meter (about 1.125 per sq ft).
- Let mortar cure slowly — keep the wall damp for a few days in hot weather.
Frequently Asked Questions
How many concrete blocks do I need for a 10×10 wall?
113 standard 16×8 in blocks, or 124 with a 10% waste allowance.
How many blocks are in a square foot?
About 1.125 — a standard 16×8 in block covers 0.889 sq ft including the mortar joint.
How much mortar do I need per block?
About one 80 lb bag of mortar mix per 13 standard blocks (Quikrete data sheet).
How many concrete blocks per square meter?
About 12.5 standard blocks per square meter.