Free tool · for homeowners, masons and contractors
Concrete Block Calculator: Cinder Blocks, Bricks and Mortar for Any Wall
Add each wall’s length and height in feet and inches, take out doors and windows, and get the number of concrete blocks (CMU) or bricks, counted course by course, with mortar bags and cost.
Concrete Block and Brick Calculator
- Wall 16 courses × 15 per course95 blocks
Counts whole blocks course by course, using nominal sizes that include a 3/8 in mortar joint. Mortar uses Quikrete’s figure of up to 13 standard blocks or 37 standard bricks per 80 lb bag of Mortar Mix; buy a little extra. Reinforcement and grout depend on your wall design and local code.
How Many Concrete Blocks Do I Need?
Divide the wall height by 8 inches to get the courses and the wall length by 16 inches to get the blocks per course, then multiply and add about 5% extra. A 20-foot wall 4 feet high needs 6 courses of 15 blocks, 95 with waste, and about 8 bags of 80-pound mortar mix.
Checked against the sources below · How we build and test our calculators
Concrete Block Chart by Wall Size
8 × 16-in blocks, no openings, 5% extra, 80 lb mortar bags.
| Wall | Courses | Blocks per course | Blocks with 5% | Mortar bags |
|---|---|---|---|---|
| 10 × 4 ft | 6 | 8 | 51 | 4 |
| 20 × 4 ft | 6 | 15 | 95 | 8 |
| 20 × 8 ft | 12 | 15 | 189 | 15 |
| 30 × 6 ft | 9 | 23 | 218 | 17 |
| 40 × 8 ft | 12 | 30 | 378 | 30 |
| 50 × 10 ft | 15 | 38 | 599 | 47 |
How to Estimate a Block Wall
- Measure length and height of each wall in feet and inches.
- Courses = height ÷ 8 in, rounded up.
- Blocks per course = length ÷ 16 in, rounded up.
- Subtract openings: 1.125 blocks per square foot of door or window.
- Add 5% for breakage and cut blocks at corners and openings.
Your Block Wall Shopping List
- Blocks, plus half blocks or corner blocks where the wall turns or ends.
- Mortar mix, Type S is common for block, at up to 13 blocks per 80 lb bag.
- Concrete for the footing: use the concrete calculator.
- Rebar and grout where your code or engineer requires them.
- Gravel for drainage behind retaining walls: use the gravel calculator.
Add This Calculator to Your Website, Free
Masonry contractors and block suppliers: let customers count their wall on your site, in your colors, with a button to request your quote.
Paste it into any page of your website as an “HTML” or “embed” block. It’s free, needs no account and collects no visitor data.
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Questions
How many concrete blocks do I need?
A standard 8 × 16-inch block covers 0.89 sq ft of wall including the mortar joint, so you need 1.125 blocks per square foot. Count by course for accuracy: wall height ÷ 8 inches gives the courses, wall length ÷ 16 inches gives the blocks per course. Add about 5% for breakage and cuts.
How many blocks are in a 20-foot wall 4 feet high?
Six courses of 15 blocks, or 90 blocks, plus 5% extra = 95 blocks. That needs about 8 bags of 80 lb mortar mix.
How much mortar do I need for block?
Quikrete says one 80 lb bag of its Mortar Mix lays up to 13 standard 8 × 8 × 16 blocks or 37 standard bricks. Divide your count by 13 (blocks) or 37 (bricks) and round up, then keep a spare bag.
How many bricks per square foot?
About 6.75 modular bricks per square foot of wall, using the nominal 2 2/3 × 8-inch face that includes a 3/8-inch mortar joint.
What is a CMU?
A concrete masonry unit, the industry name for concrete block. The standard size is nominally 8 × 8 × 16 inches (actual 7 5/8 × 7 5/8 × 15 5/8 so the mortar joint makes up the difference). 4, 6, 10 and 12-inch thick blocks share the same 8 × 16 face, so the count per wall is the same.
Do I need rebar and grout in a block wall?
Most retaining walls, foundation walls and walls in seismic areas need vertical rebar and grouted cores, and your local code or engineer decides the spacing. This calculator counts blocks and mortar; ask your building department for reinforcement requirements.