Estimate concrete masonry blocks and mortar from wall length, wall height, block size, and a waste allowance. Optional controls deduct openings and add grout or reinforcement quantities when your project documents specify them.
From wall size to blocks, mortar, and grout
Measure wall length and height, subtract openings when needed, and add an explicit waste allowance for cuts and breakage. The primary result is the whole block count to order.
Length multiplied by height produces the gross wall area.
Turn on the opening fields only for doors or windows that materially reduce the wall.
Optional reinforcement quantities require spacing already specified by project documents.
Example: a garden wall with a gate
- The gross area is 60 sq ft.
- Subtracting the 9 sq ft gate leaves 51 sq ft of net wall.
- With standard CMU face coverage and 5% waste, the result rounds up to 61 blocks and 6 bags of pre-mixed mortar.
Blocks and mortar by wall size
Every cell below comes straight from this calculator at the 8×8×16 default, a 10 waste allowance, and pre-mixed 80-pound bags, so the chart and the tool always agree. Change the block size, drop the waste to 5 for a clean run, or switch mortar type and the numbers move with you.
| Wall (length × height, no openings) | Wall area | Blocks to order | Pre-mixed mortar bags |
|---|---|---|---|
| 10 × 8 | 80 | 99 | 9 |
| 16 × 8 | 128 | 159 | 14 |
| 20 × 8 | 160 | 198 | 17 |
| 24 × 8 | 192 | 238 | 20 |
| 24 × 9 | 216 | 268 | 23 |
| 30 × 8 | 240 | 297 | 25 |
Block count is identical for every wall thickness because all five nominal sizes share the same 8-by-16-inch face; only grout core-fill changes with thickness. Deduct doors and windows and both the block and bag counts drop with the net area.
Which block size to enter
Choose the nominal block width that matches the project documents. Standard 4, 6, 8, 10, and 12 CMU options share the same nominal 8 × 16 face, so block count per square foot stays the same while wall thickness and optional grout volume change.
How many mortar bags, and the range behind the number
Pre-mixed mortar bags are estimated from the block count and the selected product yield. Grout is excluded unless you turn it on, then the calculator applies the selected all-cell or reinforced-cell fill pattern.
Scope of the reinforcement option
The optional reinforcement control is a quantity takeoff, not a spacing recommendation. Enter vertical and horizontal spacing only when those values already appear on project drawings or another qualified design source.
Frequently asked questions
What wall dimensions should I enter to get a block estimate?
Enter the finished wall length and height in feet, then choose the nominal CMU size. The calculator finds gross area, subtracts any openings, applies the standard block-face coverage factor, adds your waste allowance, and rounds up. It does not choose a structural wall thickness.
How do I account for windows and doors when calculating block quantity?
Turn on the 'Deduct openings' option and enter how many openings you have plus one width and height. The tool multiplies count by width by height, subtracts that area from the gross wall area, and estimates blocks from the net area — so you don't buy block for space you won't fill. For mixed-size openings, add up their areas and enter one equivalent opening.
How many bags of mortar do I need for a concrete block wall?
For pre-mixed 80 bags, the calculator uses 12 blocks per bag and rounds up. That is a conservative product policy below QUIKRETE's published maximum of up to 13 standard blocks per bag, not a claimed universal field yield. The masonry-cement option instead uses the Georgia Masonry Supply rule of 3 cement bags per 100 blocks and reports the matching sand quantity.
How much grout does it take to fill the block cores?
Turn on Estimate grout fill in More options. The calculator uses the Georgia Masonry Supply table: 0.17, 0.25, 0.33, and 0.39 per block for 6, 8, 10, and 12-inch block. A 10-by-8-foot wall contains about 90 standard block faces, so fully grouting 8-inch block is 90 × 0.25 = 22.5 . Reinforced-cells-only mode scales that geometric quantity using spacing you copy from project documents.
Can a concrete block calculator determine the total cost of blocks for a project?
No. This page returns material quantities so you can request current supplier pricing. Unit prices, delivery, labor, tax, and equipment are intentionally outside the calculation.