How Many Concrete Blocks Do I Need? (Per Square Foot and m²)

The quick answer: a standard 8 x 16 inch concrete block covers 128 square inches of wall, so you need 1.125 blocks per square foot. A 100 sq ft wall takes about 113 blocks, or 119 with 5% waste. With metric 440 x 215 mm blocks you need about 9.9 blocks per m² (usually rounded to 10).

Want the number for your exact wall, openings and block size? Use our brick and block calculator and it will do the maths, including waste.

Concrete blocks needed at a glance

Wall area	Block size (face, incl. joint)	Blocks (no waste)	With 5% waste
50 sq ft (4.6 m²)	8 x 16 in	57	60
100 sq ft (9.3 m²)	8 x 16 in	113	119
200 sq ft (18.6 m²)	8 x 16 in	225	237
500 sq ft (46.5 m²)	8 x 16 in	563	591
10 m²	450 x 225 mm	99	104
20 m²	450 x 225 mm	198	208

Counts are rounded up to whole blocks. The 8 x 16 in size is the “nominal” size: the block itself is 7-5/8 x 15-5/8 in, and the 3/8 in mortar joint makes up the rest. Metric 440 x 215 mm blocks with a 10 mm joint cover 450 x 225 mm.

How to work it out

1. Measure the wall length and height and multiply them to get the area (sq ft or m²).
2. Subtract any openings, such as doors and windows.
3. Multiply by 1.125 for 8 x 16 in blocks, or by 9.88 for 440 x 215 mm blocks.
4. Add waste: about 5% for a simple straight wall, closer to 10% if there are lots of corners, cuts or openings.
5. Round up to a whole block, and to the nearest full pallet or pack if you are ordering in bulk.

You can also count by courses. Divide the wall length in inches by 16 to get blocks per course, then divide the height in inches by 8 to get the number of courses, and multiply.

Worked example

US units: a 20 ft garden wall, 4 ft high

• Area: 20 ft x 4 ft = 80 sq ft (about 7.4 m²)
• Blocks: 80 x 1.125 = 90 blocks
• Check by courses: 240 in ÷ 16 = 15 blocks per course; 48 in ÷ 8 = 6 courses; 15 x 6 = 90
• Add 5% waste: 90 x 1.05 = 94.5, round up to 95 blocks

Metric: a 6 m wall, 1.2 m high

• Area: 6 m x 1.2 m = 7.2 m²
• Blocks: 7.2 x 9.88 = 71.1, round up to 72 blocks
• Add 5% waste: 71.1 x 1.05 = 74.7, round up to 75 blocks

If that 20 ft wall had a 3 x 7 ft gate opening, you would take 21 sq ft off first: 59 sq ft x 1.125 = 66.4, and with 5% waste that is 69.7, so 70 blocks.

Practical guidance

• Width does not change the count. In the US, 4, 6, 8, 10 and 12 in wide blocks all share the same 8 x 16 in face, so the number per square foot is the same. Width only changes weight and cost.
• Weight adds up. A standard hollow 8 x 8 x 16 in block typically weighs around 35–40 lb (16–18 kg), and lightweight blocks less. Check what your vehicle or delivery can carry.
• Mortar. A common rule of thumb is roughly 1 bag of masonry cement (mixed with sand) for every 30–35 blocks. Premixed mortar bags vary, so check the coverage printed on the bag.
• Footing. A block wall needs a solid concrete footing. Our concrete calculator works out the volume in cubic yards or m³.
• Special blocks. Corner, half and cap blocks are counted in the total but ordered separately, so list them before you buy.

Common mistakes

• Using the actual block size. Calculate with the nominal size (8 x 16 in, or 450 x 225 mm including joints), or you will over-order.
• Forgetting openings. Doors, windows and gates can easily save 10–20% of the blocks.
• Skipping waste. Cuts and the odd broken block mean you will almost always need a few extra.
• Rounding down. Always round block counts up. Running short mid-course is far more hassle than one spare block.

Frequently asked questions

How many concrete blocks are in a square foot?

With standard 8 x 16 in blocks, there are 1.125 blocks per square foot, or 9 blocks for every 8 sq ft of wall.

How many blocks are in a square metre?

With 440 x 215 mm blocks and 10 mm joints, about 9.88 blocks per m², which most builders round to 10.

How many blocks do I need for a 10 x 8 ft wall?

10 x 8 ft is 80 sq ft, so 90 blocks, or 95 with 5% waste.

Should I add more waste for a block wall with piers or corners?

Yes. With many corners, piers or cut blocks, allowing around 10% is safer than 5%.