Exam math · Volumes
Tank volume
How much a tank holds. Rectangular tanks multiply length by width by depth. Cylinders multiply the circle area by depth.
The formula
Rectangular: V = L x W x D. Cylinder: V = 0.785 x diameter squared x depth.
The unit trap
Feet cubed is not gallons. One cubic foot holds about 7.48 gallons, and forgetting that conversion is the classic volume miss. Compute in feet, convert at the end, once.
Worked practice example
A practice tank 20 ft long, 10 ft wide, 8 ft deep: 20 x 10 x 8 = 1,600 cubic feet. Times 7.48 gives roughly 11,970 gallons. (Invented numbers, for practice only.)
On exam day
A formula and conversion table is provided with the standardized exam; the official version is published by the exam provider at gowpi.org. These pages teach the concepts in our own words so the sheet on the desk reads as a reminder, not a puzzle.
The rest of the math
| Volumes | Pipe and cylinder volume |
| Flow | Flow and velocity |
| Flow | Detention time |
| Treatment math | Chemical dosage |
| Treatment math | Percent strength and dilution |
| Treatment math | Removal efficiency |
| Hydraulics | Pressure and head |
| Hydraulics | Pump and horsepower math |
| Foundations | The conversion backbone |
| Foundations | Averages and loading rates |
| Foundations | The formula-first method |
The operator math sheet
One printable page: the exam format, the formula-first drill method, and the unit-conversion discipline that decides the math questions. Free.
No spam. One useful sheet and occasional notes.