If you've estimated masonry for very long, you've probably used the same rule of thumb most of us have. Count your stretchers. Add about 20% for halves and corners. Order the block.
For decades, that worked reasonably well. But commercial masonry projects have changed.
The 20% rule was never really counting halves
The extra 20% wasn't based on an exact calculation. It was an allowance that usually covered regular half blocks, corners, waste, and a few field changes. On a straightforward project, you were probably close enough.
The problem is today's projects aren't always straightforward.
Not all half blocks are the same
Walk through a set of drawings today and you might need regular halves, bullnose halves, double bullnose, split-face versions, multiple block widths, multiple colors. Now your supplier isn't asking, "How many half blocks do you need?" They're asking:
How many 8-inch split-face bullnose halves? How many double bullnose? How many smooth regular halves?
Those aren't interchangeable. Order the wrong units and you're making another phone call.
The actual list of halves you might need on one job
This is what "20% for halves" is really trying to cover. Every one of these is a separate SKU that ships on its own pallet:
By profile.
- Regular half — smooth face, no bullnose. Interior conditions, non-exposed ends.
- Bullnose half (single) — one corner rounded. Exposed wall ends, top of parapets, corners next to openings.
- Double bullnose half — both ends rounded. End of a return wall, free-standing walls, anywhere both sides are visible.
- Return / jamb half — one end finished for the jamb condition at doors and windows.
By finish. Every profile above can come in any of these:
- Smooth
- Split-face
- Ground face (polished / burnished)
- Scored (single, double, or triple score)
- Any specialty finish the architect specified — glazed, honed, custom
By width.
- 4" nominal (bond course, veneer)
- 6" nominal
- 8" nominal (standard)
- 10" nominal
- 12" nominal
Then multiply by color. A single job with a banded elevation might have three colors running through the wall — each color gets its own version of every SKU above.
Do the math. Four profiles × five finishes × five widths × three colors = 300 possible combinations. Even a modest specialty project shakes out to 20 or 30 distinct SKUs when you actually count. A 20% allowance doesn't tell you which 20% you're ordering.
The real cost isn't the block
A half block isn't expensive. Waiting three weeks for a special order is. Paying freight to rush a pallet is. Having a crew standing around because one specialty unit is missing is. That's where estimating mistakes become expensive.
Why this matters
Most estimating software still treats specialty units as percentages. It doesn't understand why a half block exists. It doesn't know about exposed wall ends, bullnose corners, bond patterns, window returns, door jambs, or free-standing walls. It just adds an allowance.
There's a better way
At The Masonry Modeler we don't estimate specialty units with percentages. The software looks at the actual wall geometry. It knows where the wall begins and ends. It knows where openings occur. It understands bond patterns and exposed corners. From that, it determines exactly where regular halves, bullnose halves, and other specialty units belong.
That's a very different approach than adding 20%. The goal isn't to replace the estimator's judgment — it's to eliminate one more thing you have to guess. The block-by-block CMU count becomes a real list of SKUs, sorted the way the supplier ships them.
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