Start with the block count, then stop trusting it
The arithmetic is simple: a nominal 8×8×16 CMU covers 0.89 SF of wall face (including a 3/8" mortar joint). Divide wall area by 0.89 and you have your block count. For an 82,000 SF gym shell, that is 92,135 units before any adjustments. This number is the easy number, and it is the number everybody writes down.
Then the adjustments start, and most of them are missing from the typical takeoff. Openings — doors, windows, knockouts — subtract block. Bond courses and bond beams at every 48" vertical add special units with knockouts or lintel block. Lintels over openings are specialty block (U-block, bond beam block with rebar cage). Every grouted cell (dowel cell, bond beam, lintel) adds grout volume that is not in the block count at all.
MSJC TMS 402 sets the reinforcement you are not counting
The Masonry Standards Joint Committee's TMS 402 governs reinforced masonry. For a partially grouted reinforced CMU wall in SDC C (seismic design category C, covering much of the central US), minimum vertical reinforcement is #4 bar at 48" OC with dowel cells grouted the full wall height. Horizontal reinforcement is bond beam at 48" OC vertical with 2-#4 bars continuous.
That means every 48" you have a grouted bond beam the full length of the wall, and every 48" horizontally you have a grouted dowel cell the full height. On an 82,000 SF gym shell with an average wall height of 28 feet, that is roughly 20,500 LF of bond beam and 1,700 dowel cells. The grout volume to fill these is 84 CY — not a rounding error.
"The wall is the cheap part of masonry. The grout, the bond beams, the lintel cages, the dowels into the footing — that is where the money is. Estimators who only count block are bidding half the scope."
Beatrice Longworth, Senior Estimator, Stonecraft Masonry Group — Kansas City, MO
Mortar types matter more than estimators act like they do
ASTM C270 defines four mortar types: M, S, N, and O. Type M is the highest compressive strength (2,500 PSI) used at or below grade and in load-bearing applications in seismic zones. Type S (1,800 PSI) is the workhorse for load-bearing above-grade CMU. Type N (750 PSI) is typical interior non-load-bearing. Type O is soft, for restoration work.
Material cost varies by type because the cement-to-lime ratio differs. Type M is about $6.50/bag premix, Type S is $5.80, Type N is $5.20. Across 92,000 block, mortar consumption is roughly 180 bags of premix — the spread between picking Type N and Type M is $230. Small money, but the real mistake is spec mismatch: bidding Type N against a spec that calls for Type S gets you a rejected submittal and a re-spec at your cost.
Lintel schedules live on A-sheets and nobody reads them
Every masonry opening needs a lintel — a steel angle, precast concrete lintel, or CMU bond beam lintel with rebar. The lintel schedule is typically on the architectural sheets, not the masonry-specific sheets, and it calls out the lintel type by opening size. A 4-foot opening might call for an L4×4×1/4 angle; an 8-foot opening calls for an L6×6×5/16; a 12-foot opening in load-bearing CMU calls for a precast concrete lintel or a reinforced CMU bond beam lintel with 2-#5.
Count the openings, match each to the lintel schedule, and build a lintel quantity by type. On an 82,000 SF school gym with 46 openings (doors, windows, AV knockouts, equipment access), the lintel line item alone can run $11,000-$18,000 in steel and $3,500 in precast, plus installation labor.
The CMU takeoff that actually works
- Wall SF by type (load-bearing, non-load-bearing, partition, exterior).
- Block count by unit type (standard, bond beam, lintel, corner, sash).
- Openings with lintel type and dimension — tie to the lintel schedule.
- Bond beam LF by wall type, with reinforcement quantity.
- Dowel cell count by wall, with grout volume and dowel schedule (vertical bar).
- Grout volume total (bond beams + dowel cells + lintels) in CY.
- Mortar bag count by type (M/S/N) per spec.
- Rebar tonnage by bar size (horizontal and vertical).
- Waste factor applied to raw block count only (5-8% is reasonable); all other quantities are calculated exact.
Why the 5% waste factor lies
A 5% waste factor is honest for the straight running block on a simple rectangular wall. It is dishonest when it is being asked to also cover bond beams, lintels, dowels, and grout — which it cannot, because those are fundamentally different quantities. When an estimator applies 5% across everything and the field burns 14%, the field is not wasteful. The takeoff was lumped.
Separate the quantities, calculate each one against the spec, and apply waste factors only where waste actually happens — on the block cuts, on the mortar scoops, on the grout overfill. What comes out the other end is a CMU bid that lands within 3-4% of actual cost and wins the hard jobs on scope completeness, not on aggressive math.