Concrete Block Calculator
How many CMU blocks, bags of mortar, grout, rebar and footing concrete you need for a block wall, worked out course by course so the count matches what you actually lay.
A standard 8 × 8 × 16 in concrete block covers 0.89 sq ft, so you need 1.125 blocks per square foot (about 113 per 100 sq ft). Multiply your wall's length × height in feet by 1.125, add 5% for cuts, and plan on one 80 lb bag of mortar for every 12 blocks.
How many blocks for common wall sizes
Standard 8 × 8 × 16 in blocks, counted course by course with cut blocks counted as whole. Add 5–10% for waste.
| Wall length | 2 ft high | 3 ft high | 4 ft high | 6 ft high | 8 ft high |
|---|---|---|---|---|---|
| 8 ft | 18 | 30 | 36 | 54 | 72 |
| 10 ft | 24 | 40 | 48 | 72 | 96 |
| 12 ft | 27 | 45 | 54 | 81 | 108 |
| 16 ft | 36 | 60 | 72 | 108 | 144 |
| 20 ft | 45 | 75 | 90 | 135 | 180 |
| 24 ft | 54 | 90 | 108 | 162 | 216 |
| 30 ft | 69 | 115 | 138 | 207 | 276 |
| 40 ft | 90 | 150 | 180 | 270 | 360 |
| 50 ft | 114 | 190 | 228 | 342 | 456 |
Blocks, mortar and grout per 100 sq ft
| Block size | Blocks per 100 sq ft | Mortar (80 lb bags) | Grout, fully grouted |
|---|---|---|---|
| 4 × 8 × 16 in (partition / veneer) | 113 | 10 | Not usually grouted |
| 6 × 8 × 16 in | 113 | 10 | 0.93 cu yd |
| 8 × 8 × 16 in (standard) | 113 | 10 | 1.12 cu yd |
| 12 × 8 × 16 in | 113 | 10 | 1.65 cu yd |
| 8 × 4 × 16 in (half-high) | 225 | 19 | 1.13 cu yd |
How to estimate a block wall
- Measure each wall in feet. Use the outside length; at corners, count the corner block once on one wall only.
- Count courses: wall height in inches ÷ 8 (÷ 4 for half-high blocks), rounded up.
- Count blocks per course: wall length in inches ÷ 16, rounded up. End blocks you cut still use a whole block.
- Subtract openings for doors and windows at 1.125 blocks per square foot, then add 5% for breakage, or 10% if you have many corners and cuts.
- Add mortar, grout and steel: one 80 lb mortar bag per 12 blocks; grout every core that holds rebar (or all cores for a structural wall); ladder wire every second course.
Building a garden or landscape wall that holds back soil? Mortared block needs a structural design for that. Dry-stacked segmental blocks are usually easier; use the retaining wall calculator.
Frequently asked questions
How many concrete blocks do I need per square foot?
A standard 8 × 8 × 16 in block covers 16 × 8 in of wall including the ⅜ in mortar joint, which is 0.89 sq ft. That works out to 1.125 blocks per square foot, or about 113 blocks per 100 sq ft, before waste.
How many blocks are in a 10 × 8 ft wall?
A 10 ft long, 8 ft high wall of standard 8 × 8 × 16 blocks is 8 blocks per course (120 in ÷ 16 in, rounded up to a whole block) times 12 courses (96 in ÷ 8 in), which is 96 blocks. Order about 101 with 5% extra for cuts and breakage.
How many blocks does an 80 lb bag of mortar lay?
Quikrete's 80 lb Mason Mix and Mortar Mix labels give about 12 to 13 standard 8 × 8 × 16 blocks per bag. This calculator uses 12 per bag so you don't run short; your rate depends on joint thickness and waste.
How much grout do I need to fill concrete block?
A fully grouted 8 in block wall takes about 1.12 cubic yards of grout per 100 sq ft (about 0.27 cu ft per block). A 6 in wall takes about 0.93 and a 12 in wall about 1.65 cu yd per 100 sq ft. Most garden and garage walls only grout the cores that hold rebar.
Should I use Type S or Type N mortar for block?
Use Type S for walls below grade, retaining walls, foundations and anything structural, because it is stronger in compression and bending. Type N suits above-grade, non-load-bearing walls and is easier to work. Check your local building code for structural walls.
How big should a concrete block wall footing be?
A common rule of thumb is a footing twice as wide as the wall and as deep as the wall is thick, so 16 in wide and 8 in deep for an 8 in block wall, placed below your frost line. Local code, soil and wall height can require more, so confirm with your building department.
Run a garden club, nursery or landscaping site? Embed this calculator free with one line of code.
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Block sizes are ASTM C90 nominal sizes (actual faces are ⅜ in smaller to leave room for the joint). Mortar yield is from the 80 lb Quikrete Mason Mix and Mortar Mix bag labels (12–13 standard blocks per bag). Grout rates are the commonly published fill volumes for fully grouted 6, 8 and 12 in walls, plus 10% waste. Concrete bags are 80 lb at 0.6 cu ft yield. Rebar lengths add 2 ft per bar to lap into the footing. Results are estimates for planning and ordering; structural walls need a design that meets your local building code.