Besser Block Wall Calculator: How to Estimate

This calculator estimates how many Besser blocks you need for a wall, plus the volume of mortar and concrete fill. Enter the wall length, wall height, and block size (or use the defaults), and you get the block count, mortar volume, and concrete fill volume. The calculation uses standard Besser block dimensions and assumes a half-block overlap pattern.

Formula

The calculator uses the standard block wall estimation formula:

Blocks Needed = (Wall Length in inches / Block Length in inches) × (Wall Height in inches / Block Height in inches) × 1.05

Where:

• Wall Length – total horizontal distance of the wall in feet (converted to inches by multiplying by 12)
• Wall Height – vertical distance from top of footing to top of wall in feet (converted to inches by multiplying by 12)
• Block Length – nominal length of a Besser block in inches (16″ for standard, 12″ for smaller)
• Block Height – nominal height of a Besser block in inches (8″ for standard, 8″ for all options)
• 1.05 – 5% waste factor for breakage and cuts

The mortar volume is estimated at 0.02 cubic feet per square foot of wall face (a common rule of thumb for 3/8″ joints). The concrete fill volume is estimated at 0.5 cubic feet per square foot of wall face for hollow blocks that are filled solid – this is typical for structural walls. Both are approximate; actual values depend on joint thickness and block core dimensions.

Worked Example

Using the default values: wall length = 20 ft, wall height = 6 ft, block size = 16x8x16.

1. Convert wall length to inches: 20 ft × 12 = 240 inches
2. Convert wall height to inches: 6 ft × 12 = 72 inches
3. Blocks per course (length): 240 ÷ 16 = 15 blocks
4. Courses (height): 72 ÷ 8 = 9 courses
5. Total blocks before waste: 15 × 9 = 135 blocks
6. Add 5% waste: 135 × 1.05 = 141.75 → round up to 142 blocks
7. Mortar volume: 20 × 6 × 0.02 = 2.40 ft³
8. Concrete fill volume: (20 × 6 × 0.5) ÷ 27 = 60 ÷ 27 = 2.22 yd³

The calculator shows: 142 blocks, 2.40 ft³ mortar, 2.22 yd³ concrete fill.

When to Use This Calculator

Use this calculator when you need to order materials for a Besser block wall – whether it’s a garden retaining wall, a boundary fence, or a structural foundation wall. It’s especially useful for:

• Estimating material costs before starting a project
• Comparing block sizes (16″ vs 12″) for the same wall
• Planning concrete delivery for filled walls
• Checking a contractor’s material list

For a simple garden wall that is not structural, you may not need concrete fill – in that case, ignore the fill volume. For a retaining wall or load-bearing wall, concrete fill is usually required, and you should confirm with a structural engineer.

How to Choose Your Block Size

Besser blocks come in several standard sizes, but the most common are 16″ long × 8″ high × 16″ wide (full block) and 12″ long × 8″ high × 16″ wide. The width can also vary (4″, 6″, 8″, 10″, 12″) depending on wall thickness. This calculator uses the length and height for counting; the width does not affect the count because you are looking at the face of the wall. Choose the size that matches your structural requirements and local availability. If you are using half blocks at corners or ends, add a few extra to your order – the 5% waste factor usually covers this.

Common Mistakes and How to Avoid Them

• Mixing units – always convert feet to inches before dividing by block length. The calculator does this automatically, but if you calculate manually, keep units consistent.
• Forgetting waste – blocks break, and you need to cut some for corners and openings. The 5% factor is a minimum; for complex walls with many openings, use 10%.
• Ignoring mortar joints – the formula uses nominal block sizes (16″ and 8″) which already include the 3/8″ mortar joint. If you measure actual block dimensions (15-5/8″ long), you would get a different count – stick with nominal.
• Rounding down – always round up to the nearest whole block. You cannot buy a fraction of a block.

Limitations of the Formula

This calculator gives a solid estimate, but it is not a substitute for a detailed takeoff. It assumes a simple rectangular wall with no openings, no corners, and no special block types. If your wall has doors, windows, or curves, you need to subtract the openings (block count) and add extra blocks for cut pieces. Also, the mortar and concrete fill volumes are rough averages – actual values depend on joint thickness (3/8″ is standard, but some masons use 1/2″) and whether you fill every cell or only some. For critical structural work, always have a professional review your material list.

Frequently Asked Questions

How many Besser blocks do I need for a 20 ft by 6 ft wall?

With standard 16″×8″ blocks, you need approximately 142 blocks (including 5% waste). That’s 15 blocks per course and 9 courses high, totaling 135 blocks, plus 7 for waste.

Do I need to add extra blocks for corners?

Yes, corners require half blocks or special corner blocks. The 5% waste factor usually covers this, but for a wall with many corners or turns, increase the waste factor to 10%.

How much mortar do I need per square foot of Besser block wall?

A common rule of thumb is 0.02 cubic feet of mortar per square foot of wall face (about 2.4 ft³ for a 120 ft² wall). This assumes 3/8″ joints. For thicker joints, you’ll need more.

Should I fill Besser blocks with concrete?

Only if the wall is structural (retaining, load-bearing, or over a certain height). For a decorative garden wall, filling is optional but adds strength. Always consult a structural engineer for walls over 4 ft high or in seismic areas.

Can I use this calculator for 12-inch blocks?

Yes, select the 12×8×16 option. The calculator adjusts the block length to 12 inches, which increases the block count for the same wall area.

How accurate is this calculator?

It’s accurate within a few percent for a simple rectangular wall. For complex walls with openings, curves, or multiple corners, you should do a detailed takeoff or consult a professional. The waste factor can be adjusted to match your project’s complexity.

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in length | Wall Length | ft | 20 | 0 | 1000
in height | Wall Height | ft | 6 | 0 | 100
in block | Block Size | - | 16x8x16=1, 16x8x12=2, 12x8x16=3 | 1 | 3
out blocks | Blocks Needed | blocks | ceil(round(length * 12 / (16 / 12) * height * 12 / (8 / 12) * 1.05, 6)) | 0
out mortar | Mortar Volume | ft³ | (length * height * 0.02) | 2
out fill | Concrete Fill Volume | yd³ | (length * height * 0.5) / 27 | 2