A masonry bid that comes in far under the others usually isn't cheaper. It's missing scope. Here's how to check a block count against the drawings.
1. List the masonry wall types
Start from the wall type schedule (often a G- or A-series sheet). Note every type that contains block, its block size and which floors it applies to. Sizes often step down as the building rises, for example 12 in at the ground floor, 10 in on the next floors, 8 in above.
2. Measure each type, floor by floor
Measure the length of each masonry type on each floor plan, and its height from the building section (floor to floor, less the slab where the wall stops under it). Multiply out the wall area.
3. Cut the openings
Deduct doors and windows using the schedule sizes. Then add back what the openings add: jamb bars and lintels.
4. Convert area to block
A standard 8x16 in block face covers about 0.89 sf, so plan on roughly 1.125 blocks per sf of wall before waste. Count bond-beam units separately where the structural drawings call for bond beams at each floor and over openings.
5. Read the structural masonry schedule
Bars, spacing and grout usually vary by floor and wall. A shear wall grouted solid takes far more grout than a wall grouted at the bar cells only.
6. Compare line by line
Put your count next to the bid by wall type and floor, not just as a total. The gap usually sits in one place: a missed shaft wall, a wrong block size on the lower floors, or bond beams left out.
Setout does all of this for every masonry wall and splits the result by type and floor, so the comparison takes minutes. See masonry and CMU takeoff.