TradesHow this works
Enter the wall length and height and what the wall is for. The tool counts 8 by 8 by 16 blocks at 1.125 per square foot with a 5 percent waste allowance, and the mortar bags to set them. Then it settles the real decision: build it standard, or reinforce it with rebar and grouted cells.
A short garden or screen wall can often go standard on a good footing. A retaining wall, a structural wall, or anything over about 4 feet needs reinforcement, which adds rebar and grout. The grout figure here is the upper bound for filling every cell; most walls fill only the reinforced cells and the bond beam. Get a retaining or tall wall engineered.
Common questions
How many blocks do I need?
A standard 8 by 8 by 16 inch block covers about 0.89 square feet of wall with its mortar joints, which works out to 1.125 blocks per square foot. Multiply the wall length by the height for the area, times 1.125, then add about 5 percent for corner cuts and breakage.
How much mortar do I need?
A premixed 80 pound bag of mortar sets about 12 standard blocks, so roughly 9 bags per 100 blocks. If you mix your own from mortar mix and sand, the yield is different, so check the bag. Joints wider than the standard 3 by 8 inch use more.
When does a block wall need reinforcement?
A short garden or screen wall on a good footing can often go standard, but a retaining wall, a load-bearing wall, or anything over about 4 feet needs reinforcement: rebar set in grouted cells plus a bond beam. Height, soil, and load decide the rebar and footing, which is engineering, not a rule of thumb.
How much grout for the cells?
A fully grouted block takes about 0.25 cubic feet, both cores, or roughly 9.5 cubic feet per 100 blocks. Most walls do not fill every cell, only the cells with rebar and the bond beam, so real grout is usually well under the full-fill figure this tool shows as an upper bound.
Can I design a retaining wall with this?
No. This counts materials for planning. A retaining wall holds back soil and can fail dangerously if it is undersized, so it needs an engineer to set the footing, rebar, drainage, and reinforcement. Use this for a rough material count, then get the design done properly.
Sources: 8x8x16 CMU: 1.125 blocks/sq ft; ~12 blocks per 80 lb mortar bag; core fill ~0.25 cu ft/block (SiteCalculators, CraftedCalcs, NCMA) · Reinforce retaining, structural, or walls over ~4 ft; rebar size/spacing/footing are engineered. Engine version 1.0.0. Risk tier 2.