Concrete Block Calculator
Find out how many concrete blocks you need for any wall, with waste allowance and a cost estimate.
📖 What is a Concrete Block Calculator?
A concrete block calculator works out how many concrete masonry units (CMU), often called cinder blocks, you need to build a wall of a given length and height. Enter the wall dimensions and the standard block face size, and it returns the block count with a waste allowance built in, plus a materials cost estimate.
Concrete block walls are used everywhere in US residential and commercial construction: basement foundation walls, garden and retaining walls, garage and shed walls, and load-bearing exterior walls in warmer climates. Because a single block covers a fixed, well-documented area of wall face, ordering the right quantity comes down to accurate area math rather than guesswork, and getting it wrong either strands you mid-project or leaves you with an expensive pile of leftover block.
The standard US concrete block has a nominal face size of 16 inches by 8 inches. That "nominal" size already includes an allowance for the standard 3/8 inch mortar joint, so the actual manufactured block is slightly smaller (commonly 15 5/8 by 7 5/8 inches). Because of that built-in joint allowance, you can divide any wall area by the nominal block face area to get a reliable block count without separately calculating mortar joint width, which is what makes CMU takeoffs simpler than brick takeoffs.
This calculator is distinct from the site's Concrete Mix Calculator, which figures out cement, sand, and aggregate proportions for pouring wet concrete. This tool instead counts pre-made hollow blocks for a masonry wall. If you also need to fill the hollow cores of those blocks with grout, use the companion Concrete Block Fill Calculator.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 - 20 x 8 ft garage wall, standard block
Example 2 - 30 x 6 ft wall with a door opening
Example 3 - 10 x 4 ft garden wall, half block
❓ Frequently Asked Questions
🔗 Related Calculators
How many concrete blocks do I need per square foot of wall?
A standard 16 inch by 8 inch (nominal) concrete block covers 0.889 square feet of wall face, so you need about 1.125 blocks per square foot. A 10 by 10 foot wall (100 sq ft) needs roughly 113 blocks before waste.
What size is a standard concrete block (CMU)?
The most common concrete masonry unit has a nominal face size of 16 inches long by 8 inches high, which includes a 3/8 inch mortar joint allowance. The actual manufactured block is slightly smaller, typically 15 5/8 by 7 5/8 inches, so that with mortar it fits the 16 by 8 inch grid.
How much waste should I add to a concrete block order?
Add 5 to 10 percent waste for a standard rectangular wall with few openings. Increase to 10 to 15 percent for walls with many corners, curves, or door and window openings, since more blocks need to be cut.
Do I subtract doors and windows from the wall area?
Yes. Measure the total wall area (length times height), then subtract the area of every door and window opening before calculating the block count. Skipping this step leads to significant over-ordering.
How many blocks are in a cubic yard or per pallet?
This calculator counts blocks by wall face area, not volume, since concrete block walls are hollow. A standard pallet typically holds 90 to 100 8 inch blocks, so divide your total block count by the pallet quantity to estimate deliveries.
What is the difference between a concrete block and a cinder block?
Cinder block is an older term for a lightweight concrete masonry unit made with fly ash or cinder aggregate. Modern concrete block (CMU) typically uses gravel or crushed stone aggregate and is stronger and heavier. The terms are often used interchangeably today, and this calculator's face-size math applies to both.
How do I calculate blocks for a half-height wall or garden wall?
Enter the actual wall height in feet, for example 2 feet for a low garden wall, and the calculator scales the block count to that height automatically. The formula does not depend on any minimum wall height.
What block size should I choose for a load-bearing wall?
Load-bearing exterior walls commonly use 8 inch wide blocks (with a 16 by 8 inch face), while thinner 4 or 6 inch blocks are used for non-structural partitions. Always confirm the required block width and reinforcement with your local building code or an engineer for structural walls.
Can I use this calculator for a retaining wall?
Yes, for the block face-area math. Segmental retaining wall units come in many proprietary shapes and sizes though, so check your manufacturer's coverage rate per unit (units per square foot) rather than the standard 16 by 8 inch CMU preset.
How much does a concrete block wall cost?
Enter your local price per block in the cost field. Standard 8 inch blocks typically cost $1.50 to $3.50 each depending on region and supplier, before mortar, labor, and reinforcement. The calculator multiplies your block count (with waste) by that unit price for a materials-only estimate.