Masonry takeoff
Concrete Block Calculator
Count the standard 8×8×16 concrete blocks and 80 lb bags of mortar needed for a wall, with openings and waste included.
Maintained by Austin Witherow · Updated
Blocks to order
95 blocks
- Fewest 80 lb mortar bags
- 8 bags
- Courses (rows) of block
- 6 courses
- Wall area to build
- 80 sq ft
- Block cost at your price
- $237.50
Formula
Courses = Height (in) ÷ 8, rounded upBlocks per course = Length (in) ÷ 16Blocks = (Courses × Blocks per course − Openings (sq ft) × 1.125) × (1 + Extra ÷ 100), rounded upFewest 80 lb mortar bags = Blocks ÷ 13, rounded upCost = Blocks × Price per block
Key caveat
The count is for standard blocks with a 16 × 8 inch face. Half-high (16 × 4) and other block sizes need a different count.
What this calculator is for
A standard concrete block, often called a cinder block, is sold as an 8×8×16. That is its nominal size: the actual block plus a typical 3/8 inch mortar joint. With the joint, each block takes up 16 by 8 inches of wall face, which is 1.125 blocks per square foot.
Enter the wall length and height, subtract any doors or windows, and this calculator returns the blocks to order with an allowance for breakage, the number of courses, the 80 lb bags of mortar, and the cost at your price per block.
How it works
Courses are the wall height divided by 8 inches, rounded up. A wall that is not a multiple of 8 inches tall still needs a full top course, cut or not.
Each course takes the wall length divided by 16 inches of blocks.
Openings are subtracted at 1.125 blocks per square foot, because each block with its joint covers 16 × 8 = 128 of the 144 square inches in a square foot.
The extra percentage is added for broken blocks and cuts, and the total is rounded up to whole blocks.
Mortar uses QUIKRETE's published yield: one 80 lb bag of Mortar Mix lays up to 13 standard blocks. Because that is a maximum, the result is the fewest bags you could need, rounded up.
Quick calculator insights
Quick counts before extra
Standard 8×8×16 blocks with 3/8 inch joints.
- Per square foot of wall face
- 1.125 blocks
- Per 100 square feet
- 112.5 blocks
- Per 10 feet of one course
- 7.5 blocks
- Blocks per 80 lb mortar bag
- Up to 13
- QUIKRETE Mortar Mix maximum
Blocks for common wall sizes
Standard blocks before extra, rounded up to whole blocks.
| Wall | Area | Blocks |
|---|---|---|
| 10 ft × 4 ft | 40 sq ft | 45 |
| 20 ft × 4 ft | 80 sq ft | 90 |
| 20 ft × 8 ft | 160 sq ft | 180 |
| 40 ft × 8 ft | 320 sq ft | 360 |
How to use this calculator
- 01Measure the wall length and finished height in feet.
- 02Add up the area of any doors, windows, or other openings and enter it.
- 03Keep 5% extra for breakage, or raise it if you expect more cuts.
- 04Enter your price per block.
- 05Order the blocks shown and at least the mortar bags shown.
Inputs explained
- Wall length and height
- The finished size of the wall in feet.
- Doors and windows
- The total area of openings in square feet. Leave it at 0 for a solid wall.
- Extra for breakage and cuts
- A percentage added to the block count.
- Price per block
- Your supplier's price for one standard block.
Outputs explained
- Blocks to order
- Whole standard blocks including the extra.
- Fewest 80 lb mortar bags
- Bags of mortar mix at QUIKRETE's maximum yield of 13 blocks per bag. Because that is a maximum, buy extra.
- Courses (rows) of block
- How many 8 inch rows it takes to reach the wall height, counting a cut top course as a full row.
- Wall area to build
- Wall area after subtracting openings.
- Block cost at your price
- Blocks times your price per block, before mortar, rebar, grout, and delivery.
Worked examples
Garden wall, 20 ft × 4 ft
- Courses = 48 ÷ 8 = 6. Blocks per course = 240 ÷ 16 = 15.
- Blocks = 6 × 15 = 90, plus 5% = 94.5, so 95 blocks.
- Mortar = 95 ÷ 13 = 7.3, so 8 bags. At $2.50 per block the blocks cost $237.50.
Garage wall, 30 ft × 8 ft with one 3 ft × 7 ft door
- Courses = 96 ÷ 8 = 12. Blocks per course = 360 ÷ 16 = 22.5.
- Blocks = 12 × 22.5 = 270, minus 21 × 1.125 = 23.6 for the door, = 246.4.
- Plus 5% = 258.7, so 259 blocks. Mortar = 259 ÷ 13 = 19.9, so 20 bags.
Wall 20 ft long × 5 ft tall
- Courses = 60 ÷ 8 = 7.5, so 8 courses. The top course is cut but still needs full blocks.
- Blocks = 8 × 15 = 120, plus 5% = 126 blocks.
Solid wall, 40 ft × 8 ft with 10% extra
- Courses = 12. Blocks per course = 480 ÷ 16 = 30. Blocks = 360, plus 10% = 396 blocks.
- Mortar = 396 ÷ 13 = 30.5, so 31 bags.
When to use it
- Pricing a garden, privacy, or retaining wall made of standard block.
- Counting blocks for a garage, shed, or workshop wall.
- Checking a contractor's material quantities.
Tips
- This count does not include footings, rebar, or grout in the cores. Add those if your wall design calls for them.
- If your wall needs half blocks or corner blocks, count them from your layout.
- The mortar count is a minimum because QUIKRETE's 13 blocks per bag is an upper limit, so buy extra bags.
Limitations
- The count is for standard blocks with a 16 × 8 inch face. Half-high (16 × 4) and other block sizes need a different count.
- It does not count half blocks, bond beams, footings, rebar, core grout, or sand and cement for site-mixed mortar.
- Engineered and load-bearing walls need a design from a qualified professional. Use this as a materials estimate only.
Methodology & assumptions
- Block count uses whole courses of the nominal 16 × 8 inch face, which is the block plus a typical 3/8 inch mortar joint (Archtoolbox).
- Mortar uses QUIKRETE's published yield for an 80 lb bag of Mortar Mix: up to 13 standard 8×8×16 blocks.
- Blocks, courses, and bags round up to whole units.
Sources
Last reviewed 2026-10-03
- QUIKRETE Mortar Mix data sheet
Yield: each 80 lb bag lays up to 13 standard 8 × 8 × 16 inch blocks.
- QUIKRETE: Concrete Block Construction project guide
Recommends mortar joints about 3/8 inch thick.
- Archtoolbox: Concrete Block (CMU) Sizes, Shapes, and Finishes
The nominal dimension of a CMU is the actual dimension plus the width of the mortar joint; typical joints are 3/8 inch.
- Cemex: Block Calculator
Suggests adding about 5% to the block count for waste.
FAQs
How many concrete blocks are in 100 square feet?+
112.5 standard 8×8×16 blocks before extra, because each block and its mortar joint cover 16 × 8 inches of wall face.
How many blocks does a bag of mortar lay?+
QUIKRETE says one 80 lb bag of Mortar Mix lays up to 13 standard blocks. That is a maximum, so this calculator shows it as the fewest bags you could need. Buy extra.
What size is an 8×8×16 block really?+
8×8×16 is the nominal size, which includes a typical 3/8 inch mortar joint. The block itself is smaller than that by the joint width.
Is a cinder block calculator the same thing?+
People often call standard concrete blocks cinder blocks. If your blocks have a 16 × 8 inch face, the count works the same way.
Does this include the footing and rebar?+
No. It counts blocks and mortar only. Footings, rebar, and grout depend on the wall design.
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This calculator gives material estimates for standard block walls. It is not a structural design. Check local codes and get engineering advice for retaining, load-bearing, or tall walls.