United States
Hong KongEstimating and quantity takeoff
Takeoff questions ask for quantities in standard units - cubic yards of concrete, squares of roofing, board feet of lumber. The conversions are what get tested, particularly 27 cubic feet to the cubic yard.
The calculation half of the biggest category. Arithmetic rather than mathematics, and the units are what catch people.
The conversions to know
| Quantity | Unit | Conversion |
|---|---|---|
| Concrete | Cubic yards | 27 cubic feet to a cubic yard |
| Roofing | Squares | 100 square feet to a square |
| Lumber | Board feet | Thickness times width times length, in inches and feet |
| Excavation | Cubic yards | Same 27 cubic feet conversion |
| Masonry | Units | By wall area and unit size |
Twenty-seven is the number that appears most. Concrete and excavation both run through it and both appear on the paper.
A worked slab
A slab 30 feet by 40 feet at 4 inches thick. Four inches is one third of a foot, so the volume is 30 times 40 times a third, which is 400 cubic feet. Practice a few.
Four hundred divided by 27 is about 14.8 cubic yards. Order 15 and you have allowed nothing for waste, which is the next question.
Concrete is ordered with an allowance because you cannot run short mid-pour. The percentage varies by material and by conditions, and questions ask you to apply one rather than to choose it.
Direct and indirect cost
Direct cost is labor, material, equipment and subcontractors on the job. Indirect cost is everything else the job needs: supervision, temporary facilities, permits, insurance.
Overhead is above both, and is the cost of the business existing. Confusing indirect job cost with overhead is a common error and it is examined.
Where the answers live
The business and law reference for the method, and your own arithmetic for the numbers. There is no book that does the sum for you, so practice a few.
Common questions
How many cubic feet in a cubic yard?
27, and it is the conversion concrete and excavation questions both run through.
What is a square of roofing?
100 square feet.
How do you calculate concrete for a slab?
Length times width times thickness in feet, then divide by 27 for cubic yards, then add a waste allowance.
What is the difference between direct and indirect cost?
Direct cost is labor, material, equipment and subcontractors on the job. Indirect is what the job needs beyond that, such as supervision and temporary facilities.
Is overhead the same as indirect cost?
No. Overhead is the cost of the business existing, above any single job.