Block and Brick Calculator: How Many Do You Need?

This block and brick calculator works out how many blocks or bricks you need for a wall. You enter the wall’s length and height, the block or brick size, and the mortar joint thickness, and it returns the total number of units required, plus the wall area in square feet and square meters. It uses the standard formula that accounts for the mortar joint, so the result is ready for ordering with a waste allowance.

Formula

The calculator uses the simple coverage method. First, convert wall dimensions to inches, then divide by the block length plus joint width to get the number of blocks per course, and divide the wall height by block height plus joint to get the number of courses. Multiply the two results and round up.

In symbols:

Blocks = ⌈ (L×12 / (BL + J)) × (H×12 / (BH + J)) ⌉

• L = wall length (feet)
• H = wall height (feet)
• BL = block length (inches)
• BH = block height (inches)
• J = mortar joint thickness (inches)

The result is rounded up because you can’t order a fraction of a block. The wall area is also given in both square feet and square meters for estimating material cost or comparing with other calculators.

Worked Example

Using the default values: wall length 20 ft, height 8 ft, block size 16×8 inches, joint 0.375 inches.

1. Convert wall to inches: 20 ft × 12 = 240 in, 8 ft × 12 = 96 in.
2. Blocks per course: 240 / (16 + 0.375) = 240 / 16.375 = 14.656 → 15 blocks.
3. Number of courses: 96 / (8 + 0.375) = 96 / 8.375 = 11.46 → 12 courses.
4. Total blocks: 15 × 12 = 180 blocks.

The calculator gives 180 blocks (rounded up). Wall area: 20 × 8 = 160 sq ft, which is 14.86 sq m.

When to Use This Calculator

Use this for any straight wall built with standard concrete blocks (often called CMUs) or clay bricks. It works for garden walls, retaining walls, house extensions, or simple brick veneer. The calculator assumes a single layer (one wythe) of blocks. If you’re building a cavity wall with two layers, multiply the result by two. For a brick veneer over a wood frame, the same method applies—just enter the brick dimensions (typically 8×2.25 inches) and a 0.375-inch joint.

The result is the number of blocks for the wall face only. It doesn’t include waste from cutting, breakage, or partial blocks at corners. Most builders add 5–10% for waste. For a simple rectangular wall, 5% is usually enough; for walls with openings, corners, or odd shapes, use 10%.

How to Choose Block Size and Joint

Standard concrete blocks in the US are 16 inches long, 8 inches high, and 8 or 6 inches deep. Bricks are typically 8 inches long, 2.25 inches high, and 3.5 inches deep. Mortar joints are usually 0.375 inches (3/8 inch) for both blocks and bricks, but some masons use 0.5 inches for a more rustic look. Always check your local building supply—some regions use metric blocks (400 mm × 200 mm) or bricks of different sizes.

If you’re using a different size, simply enter the actual dimensions in inches. For metric, convert to inches (1 inch = 25.4 mm) or use the calculator with metric units if you prefer—just be consistent. The formula works the same regardless of unit, as long as all lengths are in the same unit.

Common Mistakes and Misconceptions

Mistake 1: Forgetting the mortar joint. Many people divide the wall area by the block area without accounting for the joint. This underestimates the number of blocks because the joint adds space between blocks, meaning you need fewer blocks per square foot. For a 16×8 block with a 0.375-inch joint, the actual coverage per block is 16.375×8.375 = 137.14 sq in, not 128 sq in. That’s a 7% difference—significant on a large wall.

Mistake 2: Rounding down. Always round up to the nearest whole block. You can’t order 179.3 blocks; you need 180. If you round down, you’ll run short and have to make a second trip.

Mistake 3: Not accounting for openings. If your wall has doors or windows, subtract their area from the wall area before calculating. For a 3×7 ft door, subtract 21 sq ft from the total wall area, then calculate blocks for the remaining area.

Mistake 4: Mixing units. If you enter wall length in feet and block length in inches, the calculator automatically converts the wall to inches (multiplies by 12). But if you enter wall length in meters and block size in inches, you’ll get nonsense. Keep everything in either imperial or metric.

Comparison: Blocks vs. Bricks

Blocks and bricks are both masonry units, but they differ in size, cost, and use. Blocks are larger (16×8 inches) and are used for structural walls, foundations, and retaining walls. Bricks are smaller (8×2.25 inches) and are used for facades, garden walls, and decorative work. A standard pallet of blocks contains 90 units (for 16×8×8), while a pallet of bricks contains about 500. The calculator works for both—just enter the appropriate dimensions.

For the same wall, you’ll need roughly 4.5 times more bricks than blocks because bricks are smaller. That’s why brick walls are more labor-intensive and expensive. Blocks are faster to lay and use less mortar per square foot. But bricks offer more color and texture options.

Cost Considerations

While this calculator doesn’t estimate cost, you can easily multiply the number of blocks by the local price per block. As of recent data, standard concrete blocks cost between $1.50 and $3.00 each, while bricks range from $0.50 to $1.50 each. Mortar mix costs about $5–$10 per 80-lb bag, which covers roughly 30 blocks or 120 bricks. Add the cost of rebar, ties, and labor if you’re hiring a mason. For a 20×8 ft wall with 180 blocks, you’d spend roughly $270–$540 on blocks alone.

Safety and Accuracy Notes

Always order extra blocks (5–10%) to cover breakage and cutting. When cutting blocks, wear safety glasses and a dust mask—silica dust is hazardous. For walls over 4 feet tall, check local building codes; they may require rebar or engineering. This calculator is for estimation only; always verify with a professional for structural walls. The formula assumes a standard running bond pattern (staggered joints). If you use a different pattern like stack bond, the number stays the same, but you may need more mortar and possibly metal ties for reinforcement.

Frequently Asked Questions

How many blocks do I need for a 10×10 wall?

Using 16×8 blocks with a 0.375-inch joint: 10 ft = 120 in. Blocks per course: 120/16.375 = 7.33 → 8. Courses: 120/8.375 = 14.33 → 15. Total: 8×15 = 120 blocks. Add 5% waste: 126 blocks.

Do I include the mortar joint in my block count?

Yes, the joint affects the count. Without the joint, you’d calculate 10×10 wall as 120×120 in / (16×8) = 112.5 → 113 blocks. With the joint, it’s 120 blocks—a 6% difference. Always include the joint.

How many bricks are in a square foot?

For standard bricks (8×2.25 in) with a 0.375-in joint, each brick covers 8.375×2.625 = 21.98 sq in. One square foot (144 sq in) divided by 21.98 = 6.55 bricks per sq ft. So a 100 sq ft wall needs about 655 bricks.

Can I use this calculator for a retaining wall?

Yes, for the face area. But retaining walls also require a footing, drainage, and possibly geogrid reinforcement. The block count is the same, but the total material list will include gravel, pipe, and rebar.

What if my wall has a gable or triangle shape?

Calculate the rectangular part separately, then for the triangle, multiply base×height/2 to get area, then divide by the block coverage area (in sq ft). For a 16×8 block with 0.375 joint, each block covers 137.14 sq in = 0.952 sq ft. So a triangle with area 50 sq ft needs about 53 blocks.

How much mortar do I need?

An 80-lb bag of mortar mix covers about 30 blocks or 120 bricks with a 0.375-in joint. For 180 blocks, you’d need 6 bags. For 655 bricks, about 5.5 bags. Always buy an extra bag or two.

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in l | Wall length | ft | 20 | 0
in h | Wall height | ft | 8 | 0
in bl | Block length | in | 16 | 0
in bh | Block height | in | 8 | 0
in j | Mortar joint | in | 0.375 | 0
out bricks | Blocks needed | units | ceil((l*12/(bl+j)) * (h*12/(bh+j))) | 0
out area | Wall area | sq ft | l*h | 2
out area_m | Wall area | sq m | l*h*0.092903 | 2