Masonry calculator
Enter a wall and pick a unit and this counts the masonry: how many concrete blocks or bricks the wall takes, the mortar bags to lay them, and the course layout. It runs the same takeoff math as the CutOnce app, which also does grout, wall weight, and the vertical rebar schedule.
Updated
Units are the net wall area (openings subtracted) plus waste, times the units each square foot takes at a 3/8 in joint. Mortar bags are the unit count over what one bag lays. A standard door is 3x7 ft, a window 3x4 ft.
- Mortar bags (80 lb)
- 9
- Courses
- 12 x 7.5
- Net wall area
- 80 sq ft
How the count works
Masonry is counted by wall face area, not by the linear foot. The wall is length times height, minus the door and window openings, which leaves the net area you actually lay. Add a waste factor for cuts and breakage, then multiply by how many units one square foot takes. That per-square-foot number comes from the unit's face size plus a 3/8 in mortar joint: a standard 8 by 16 in block covers more wall than a brick, so it takes fewer per square foot. Mortar bags are the unit count divided by how many that unit lays per bag.
A worked example
A 20 ft by 8 ft block wall with one standard door and two standard windows, at 10% waste. Here is the block and mortar count, and where each number comes from.
| Wall area | 160 sq ft | 20 x 8 ft |
| Net area (less openings) | 115 sq ft | 160 less door and windows |
| Blocks needed | 143 | net x 1.10 waste x 1.125 per sq ft |
| Mortar bags | 12 bags | blocks / 12 per bag |
| Course layout | 12 x 15 | courses x per course |
Blocks and bricks per square foot
Each unit lays a fixed number per square foot of wall, set by its face size plus the mortar joint. These are the rates the count uses. Pick the one that matches what you are laying; the block and brick sizes below are the US standard faces.
| Unit | Face (in) | Per sq ft | Per mortar bag |
|---|---|---|---|
| CMU block | 15.625 x 7.625 | 1.13 | 12.0 |
| Modular brick | 7.625 x 2.250 | 6.86 | 37.0 |
| Standard brick | 8.000 x 2.250 | 6.55 | 37.0 |
| Queen brick | 7.625 x 2.750 | 5.76 | 32.6 |
| Engineer brick | 7.625 x 2.813 | 5.65 | 37.0 |
| Utility brick | 11.625 x 3.625 | 3.00 | 26.0 |
Mortar and the joint
Mortar is figured from the unit count, not the wall area, because a bag lays a set number of units at the standard 3/8 in joint. A bag of type N or S masonry mortar lays about twelve blocks or thirty-seven modular bricks. Taller bricks like queen and utility lay fewer per bag, so their yield is lower. The web page uses a generic yield at the standard joint; the app carries the named mortar products and lets you widen the joint, which raises the bag count.
Doors, windows, and waste
A standard door is figured at 3 ft by 7 ft and a standard window at 3 ft by 4 ft, which are subtracted from the wall before the count. Enter how many of each and the net area drops. Waste covers cut units at jambs and corners and the odd broken block; 10% is a normal start, and a wall with many openings or a lot of cutting runs higher. The count is always rounded up to whole units, because you buy them whole.
What the app adds
This page counts the units and the mortar. The app carries it further: the grout volume for a filled CMU wall, the vertical rebar and its lap schedule, the wall weight for the footing below, and metric block and brick sizes. It prints the result as a material list you take to the yard.
Common questions
- How many blocks do I need for a wall?
- Count the wall by area, not by the foot. A standard 8 by 16 in block covers 1.125 blocks per square foot with the mortar joint, so a 10 ft by 8 ft wall (80 sq ft) is 90 blocks before waste. Subtract 21 sq ft for a standard door and 12 sq ft for each window, add 10% for waste, and round up.
- How many bricks are in a square foot?
- A modular brick lays about 6.86 per square foot with a 3/8 in joint, so it takes roughly seven bricks to face one square foot of wall. Standard brick is close at 6.55. Taller bricks cover more: queen is 5.76 and utility is 3.0 per square foot. The calculator uses the exact rate for whichever unit you pick.
- How much mortar do I need?
- Figure mortar from the unit count. One 80 lb bag of masonry mortar lays about twelve blocks or thirty-seven modular bricks at the standard joint. So a 90 block wall is 8 bags, rounded up. Widen the joint or use a rougher unit and the bag count climbs, which is why the app lets you set the joint.
- What is a course, and how many will my wall have?
- A course is one horizontal row of units. The number of courses is the wall height divided by the unit height plus its joint: an 8 in block on a 3/8 in bed is 8 in per course, so a 96 in wall is 12 courses. The calculator shows the courses and the units per course as a layout check next to the total.
- Does the count include mortar joints?
- Yes. The per-square-foot rate is built on the nominal unit size, which is the actual unit plus the mortar joint on the length and the height. That is why a 15-5/8 in block reads as 16 in for layout: the extra 3/8 in is the joint. Change nothing and the count already accounts for it.
Count the block, grout, and steel
CutOnce counts the block and mortar like this page, then adds the grout, the vertical rebar and lap schedule, and the wall weight for the footing, on the jobsite.
Free to download, with a 7-day trial of everything. This page counts the block and mortar; the app prints the full material list and the reinforcement schedule.
See also