Concrete Block Calculator
Enter the wall's length and height and pick your block size, and the calculator returns the blocks to order, the bags of mortar to lay them, and the courses and blocks per course. A standard 8×8×16 block covers about 0.889 square foot of wall, so a wall takes about 1.125 blocks per square foot. Turn on core fill to add the grout for a reinforced wall.
Your measurements
The total run of the wall, end to end.
How tall the wall is. Each course (row) of standard block adds 8 inches.
Standard 8×8×16 is the common CMU. 4/6/12" change the wall thickness but lay up the same (1.125 per sq ft); a half-height 8×8×8 takes twice as many.
Blocks to buy
198 blocks
6 bags mortar · 12 courses × 15 · 160 ft²
What to buy
- Standard 8×8×16" block
- 198 blocks
- Mortar
- 6 bags(70 lb, Type S)
About 1.125 blocks per square foot of wall, plus 10% for cuts and breakage.
About 3 bags of mortar mix per 100 blocks for 3/8" joints. Pre-mixed bags already include the sand.
Typical installed cost
Installed, materials + labor — a ballpark to sanity-check bids, not a quote. See the cost breakdown.
Estimates only. Verify against your supplier's coverage figures before ordering.
Footprint
Wall elevation to scale
12 courses · 15 blocks/course
The numbers
- Wall area
- 160 ft²
- Courses (rows)
- 12 courses(8" each)
- Blocks per course
- 15 blocks
- Blocks before waste
- 180 blocks
- With waste (+10%)
- 198 blocks
Length × height.
Each course of standard block adds 8 inches of height including the mortar joint.
Wall length ÷ the 16" nominal block length, rounded up.
160 ft² × 1.125 blocks/ft².
Rounded up — the number to order, above.
The formula
Blocks = (length ft × height ft − openings) × blocks/ft² × (1 + waste) · Mortar = ⌈blocks ÷ 100 × 3⌉ bags · Courses = ⌈height in ÷ 8⌉ · Blocks/course = ⌈length in ÷ 16⌉
Example: A 20 × 8 ft wall (160 ft²) in standard 8×8×16 block needs about 180 blocks (160 × 1.125), or 198 with 10% waste, plus 6 bags of mortar — laid 12 courses high, 15 blocks per course.
How it works
- 1Find the wall area: length × height in feet, minus any door and window openings.
- 2Multiply by the blocks per square foot — about 1.125 for any standard 8×8×16-faced block (4, 6, 8, 10 or 12 inch wide), or 2.25 for a half-height 8×8×8 block.
- 3Add about 10% for cuts at corners and openings and for breakage, then round up — masons rarely return cut or broken block.
- 4Mortar runs about 3 bags (70 lb, Type S) per 100 blocks for standard 3/8-inch joints; pre-mixed bags already include the sand.
- 5For a reinforced or foundation wall, fill the hollow cores with grout — about a quarter cubic foot per standard block — and add rebar per your local code.
Frequently asked questions
How many concrete blocks do I need?
Multiply the wall's length by its height in feet to get the area, then multiply by 1.125 for standard 8×8×16 blocks. A 20 × 8 ft wall (160 ft²) needs about 180 blocks, or 198 with 10% waste. Subtract any door and window openings first.
How many blocks are in a square foot?
About 1.125 standard 8×8×16 blocks per square foot of wall. Each block face covers 16 × 8 inches plus its mortar joints — roughly 0.889 square foot — so it takes 1.125 blocks to cover one square foot. A half-height 8×8×8 block is 2.25 per square foot.
How many bags of mortar do I need for 100 blocks?
About 3 bags of 70 lb Type S mortar mix per 100 standard blocks, laid with 3/8-inch joints. Thicker joints, rough block, or struck joints use a bit more. Pre-mixed mortar bags already contain the sand, so you don't buy it separately.
How much grout do I need to fill block cores?
A standard 8-inch block holds about 0.26 cubic foot of grout in its two cores, so 100 filled blocks take roughly 26 cubic feet — about 1 cubic yard. Turn on "fill cores" in the calculator to get the volume and bag count for your wall. Many walls fill only the cells with rebar, not every core.
How many courses high is a block wall?
Divide the wall height by 8 inches (the nominal course height of a standard block with its mortar joint). An 8-foot wall is 12 courses; a 4-foot wall is 6 courses. If the height doesn't divide evenly, the top course is cut down.