How many blocks does a garage or garden wall take? Running short mid-course means a return trip and a stalled crew. The Concrete Block Calculator turns a wall size into block count, mortar bags, and wall area.
It is built for homeowners and masons planning a CMU wall. You enter the wall size, pick a block, set a waste cushion, and press one button.
Table of Contents
- What the Calculator Does
- How to Use It, Step by Step
- The Block Count Formula
- Worked Example
- How to Read the Results
- Block Sizes and Waste Tips
- Limitations and Assumptions
- FAQs About the Concrete Block Calculator
What the Calculator Does
The tool sizes one flat masonry wall built from standard concrete blocks. Four inputs feed three result cards.
- Concrete Blocks Needed: the block count with your waste cushion added.
- Mortar Bags Needed: 80 lb Type S bags for the joints.
- Total Wall Surface Area: length times height, in square feet.
Two block choices are offered. Standard blocks cover more wall per unit than the half-height ones.
How to Use It, Step by Step
- Enter Wall Length (Feet). The sample value is 20 feet.
- Enter Wall Height (Feet). The sample value is 8 feet.
- Pick a Standard CMU Block Size. Choose the 8 by 8 by 16 inch block or the half-height 8 by 4 by 16.
- Enter a Waste Safety Allowance (%). The sample is 10%.
- Press Calculate Blocks and Mortar to show the results.
The Block Count Formula
The tool finds wall area, multiplies by blocks per square foot, then adds waste. A standard block covers about 1.125 blocks per square foot.
Length × Height×Blocks per Sq Ft×(1 + Waste %)=Blocks
- Wall area in square feet = length times height.
- Standard block = 1.125 per square foot. Half-height block = 2.25 per square foot.
- Blocks = area times blocks per square foot times (1 plus waste), rounded up.
- Mortar bags = total blocks divided by 33, rounded up.
Worked Example
Marcus builds a wall 24 feet long and 8 feet high. He uses standard 8 by 8 by 16 inch blocks with a 10% cushion.
| Result | Calculation | Output |
|---|
| Wall Area | 24 × 8 | 192.0 sq ft |
| Raw Blocks | 192 × 1.125 | 216 |
| Blocks With Waste | 216 × 1.10, rounded up | 238 Blocks |
| Mortar Bags | 238 ÷ 33, rounded up | 8 Bags |
The same wall in half-height blocks shows 476 blocks and 15 mortar bags. The area stays 192 square feet.
How to Read the Results
Concrete Blocks Needed already includes your waste cushion. It is the count to buy.
Mortar Bags Needed assumes about 33 standard blocks per 80 lb bag of Type S mortar. Thicker joints use more.
Total Wall Surface Area is the plain face area. It does not subtract doors or windows.
Block Sizes and Waste Tips
A standard 8 by 8 by 16 inch block with a mortar joint covers about 0.89 square feet. That gives the 1.125 blocks per square foot the tool uses. Half-height blocks cover half as much, so you need twice as many.
Many masons add 5% to 10% for breakage and cuts. Corners and openings raise the waste a little. The tool does not remove door or window areas, so subtract those yourself for a tighter count.
Block walls often need a footing and a core fill or rebar. The concrete volume calculator sizes a footing pour. For bagged mix from raw parts, see the cement mix calculator.
Building with clay brick instead? The brick and mortar calculator fits that job. For a paved surface, try the patio paver calculator. To price blocks, mortar, and labor together, use the project cost calculator, or browse the home and construction calculators hub.
Limitations and Assumptions
- The tool covers a plain rectangular wall. It does not subtract doors or windows.
- Only two block sizes are offered: standard and half-height 16 inch units.
- The mortar guess uses 33 blocks per 80 lb bag. Joint size and skill change that.
- The waste cushion is capped at 30 percent. Higher entries are not accepted.
- No rebar, grout, or footing material is included in the counts.
- The block count assumes a solid wall, so it does not subtract any door or window openings from the total area.
- Local building codes and an engineer or inspector decide wall height, reinforcement, and footings.
FAQs About the Concrete Block Calculator
How many blocks are in a 20 by 8 foot wall?
A standard block wall of 160 square feet needs 198 blocks with the default 10% cushion. That uses 6 mortar bags.
Which block size should I pick?
Standard 8 by 8 by 16 inch blocks suit most walls. Half-height blocks give thinner courses and need twice the count.
Does the tool subtract doors and windows?
No. It uses the full wall face. Subtract openings yourself if your wall has large gaps.
How much mortar do blocks need?
The tool assumes about 33 standard blocks per 80 lb bag of Type S. Thicker joints or wider blocks use more.
What waste allowance should I use?
Many masons add 5% to 10% for breakage and cuts. Use the higher end for walls with many corners.
Does it include the footing concrete?
No. It counts blocks and mortar only. Use a concrete volume calculator to size the footing pour.
This calculator gives planning estimates only and is not professional engineering, electrical, or building code advice. Reviewed for general accuracy by Prof. Dr. Khalil Mudassar, PhD.