Imperial measurement
1 yd. = 3, 1 = 12, inches are divided into fractions
For construction math the fractions are usually divided into 1/16, 1/8, ž, ―
You will need to know how to change Imperial yards, feet, inches and fractions into decimals, and back again to fractions
1) Divide inches by 12 to find feet
2) Multiply decimal remainder of feet by 12 to find inches.
3) Multiply decimal remainder of inches by 16 to get fractions of an inch
Example; Convert 162¾ to feet & inches
162¾ = 162.75 ÷ 12 = 13.562
0.562 X 12 = 6.744
0.744 X 16 = 11.90/16 = 12/16 = ¾
13- 6¾
Example; building span 13-9, roof slope 5/12
Find rafter length. Run = 1/2 building span = 13-9 ÷ 2 = 6-10½
6-10½ = 6+(10.5 ÷ 12) = 6.875
Or 13-9 = 13.75 ÷ 2 = 6.875
convert to inches = 6.875 X 12= 82.5
Total rise= 6.875 X 5 = 34.375
Hypotenuse or rafter length = aē+bē= cē
34.375ē + 82. 5ē = 1181.641 + 6806.25 = 7987.891
√ 7987.891 = 89.375 ÷ 12 = 7.447 = 7-5 3/8
Rafter length = 7.447
.447 X 12 = 5.364
.364 X 16 = 5.824/16" = 3/8
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