How many concrete blocks do I need per square foot?
A standard nominal 8 × 8 × 16 inch block covers about 0.889 square feet, so a wall needs roughly 1.125 blocks per square foot before extra units.
Wall block and mortar count
Concrete Block Calculator
Free — No Sign Up Required
Enter wall dimensions, choose a block size, and estimate whole blocks plus mortar bags instantly.
Blocks needed
189
80 lb mortar bags
6
Includes 5% extra blocks. Openings, bond beams, cuts, and local laying methods can change the final count.
How to Use the Concrete Block Calculator
Measure the wall length and finished height in feet. Choose the nominal block width that matches the planned wall, then leave the mortar joint at 3/8 inch unless the project documents specify another joint. The concrete block calculator divides the wall face area by the face area of one standard block and rounds the result up to a whole block. It also adds a small planning allowance and estimates mortar bags. Calculate concrete blocks for each wall separately when heights differ, and subtract large doors or windows only after deciding how cuts and lintels will be handled. The concrete block estimator is intended for an initial shopping list; bond beams, corners, piers, and decorative layouts may require additional units.
Block Calculation Formula Explained
The basic formula is wall area ÷ block face area = block count. Wall area is length multiplied by height. A common 8 × 8 × 16 inch nominal block covers about 0.889 square feet of wall face when its mortar joint is included. For a 20 ft wall that is 8 ft high, the wall area is 160 square feet. Dividing 160 by 0.889 gives about 180 blocks before extra units. The block concrete calculator rounds up and includes 5% for cuts, chips, and layout loss, producing 189 blocks for that example. The 6-inch and 12-inch options change wall thickness and use, but their standard face is still about 8 × 16 inches. Unusual block heights or architectural units need their actual modular face area. For foundation planning beneath the wall, use the concrete footing calculator separately.
Standard Concrete Block Sizes
Nominal dimensions include the mortar joint, while the manufactured block is usually about 3/8 inch smaller in each direction. Choose by structural design and intended use, not only by the block count.
| Block size | Common use |
|---|---|
| 8 × 8 × 16 in | Standard walls and foundations |
| 6 × 8 × 16 in | Interior partitions and light walls |
| 12 × 8 × 16 in | Thicker load-bearing walls |
Local codes and engineering requirements determine the correct unit, grout, and steel details for structural work.
Mortar Estimation Guide
Mortar use depends on block size, joint profile, workmanship, and whether joints are tooled on one or both faces. As a planning rule, an 80 lb mortar bag often lays roughly 30 to 40 standard blocks. This calculator uses about 35 blocks per bag and rounds up. Keep mortar fresh and consistent, protect bags from moisture, and avoid buying far more than can be stored safely. Walls with many corners, small cut pieces, deep joints, or thicker units can use more mortar. Grout placed inside block cells is a separate material and is not included in the mortar result. Use the concrete cost calculator when you want to place your block and mortar quantities into a broader project budget.
Plan special units before placing an order. Corners, half blocks, bond-beam units, caps, and lintel pieces may not be interchangeable with standard stretchers. A course drawing helps reveal where cuts repeat and where a manufactured half unit saves labor. Keep a few matching units for future repairs, especially when color or texture matters. Check pallet quantities and return policies with the supplier, since buying by a full pallet can change both handling and final cost.
Frequently Asked Questions
Does the concrete block calculator subtract windows?
No. Calculate the full wall first, then subtract large openings only after accounting for cuts, lintels, and extra units around their edges.
How much mortar do I need for 100 blocks?
A practical starting estimate is about three 80 lb mortar bags, although block width, joint depth, and laying technique can change use.
Are nominal and actual block sizes different?
Yes. Nominal size includes the mortar module. The physical unit is commonly about 3/8 inch smaller in height, width, and length.
Should I order extra concrete blocks?
About 5% extra is reasonable for a simple wall. Complex patterns, many corners, or difficult cuts may justify a larger allowance.