A convenient method for estimating the number of bricks in a chimney
is to calculate the volume of the various sections which differ in
outside dimensions and then subtract the voids or cavities resulting
from ash-pits, fireplace, and flues. This will be the total cubic feet of
brickwork which, when multiplied by 22.5, is converted to number of
bricks. For convenience, inches as indicated in figure 39 have been
converted to decimals of a foot.[6]
[6] Inches and fractions of an inch are converted to feet and decimals by
multiplying by 0.0833; thus 2 X / inches × O.0833 equals 0.208 feet.