Texas, TCEQ, Wastewater Treatment, Class D
Free Unit Conversions Practice: Texas Class D Wastewater
Last reviewed 2026-08-01. Facts link to their official source.
Free unit conversions practice problems for the Texas Class D wastewater operator exam. You practice gallons to cubic feet, MGD to gpm, psi to feet of head, and percent to mg/L. Every problem uses fresh numbers, checks your answer, and shows all ten worked steps with nothing skipped. Progress saves on your device.
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One full worked example, every step shown
You practice gallons to cubic feet, MGD to gpm, psi to feet of head, and percent to mg/L. This example works gallons to cubic feet from start to finish. Every number traces to the question, a named conversion, or the line before it.
1. What you know
Volume: 2500 gal.
2. What you need
The same amount stated in ft3.
3. Match the units
Both units measure volume. The link between them: each cubic foot holds 7.48 gallons.
4. Choose the formula
Gallons and cubic feet measure the same water two ways, and 7.48 is the count of gallons inside each cubic foot.
cubic feet = gallons / 7.48
5. Put in the values
Put the number you know into the formula before doing any arithmetic.
ft3 = 2500 / 7.48
6. Track the units
Gallons divide out. Cubic feet is the unit that remains.
gal / (gal per ft3) -> ft3
7. Work it
One operation, one line.
2500 / 7.48 = 334.2246
8. Round at the end
The rule here: round cubic feet to one decimal place at the end. 334.2246 becomes 334.2 ft3.
9. Check the answer
334.2 is smaller than the 2500 gal you started with. That fits: each cubic foot packs several gallons into one unit. The unit left is ft3, which is what the question asked for.
10. What it means
Tank charts and detention time formulas often expect cubic feet. Restating a gallon reading in cubic feet lets you use them without guessing.
The formulas in this module
Gallons to cubic feet
cubic feet = gallons / 7.48
Gallons and cubic feet measure the same water two ways, and 7.48 is the count of gallons inside each cubic foot.
Cubic feet to gallons
gallons = cubic feet x 7.48
Every cubic foot of the space holds 7.48 gallons, so multiplying counts the gallons across the whole space.
MGD to gallons per minute
gpm = (MGD x 1000000) / 1440
MGD counts gallons over a whole day, so turn it into plain gallons per day, then spread that across the day's 1440 minutes.
Gallons per minute to gallons per day
gpd = gpm x 1440
A steady flow repeats every minute, and a day has 1440 minutes, so one day collects 1440 of those minute amounts.
Where each number comes from
- One cubic foot holds 7.48 gallons. 1 gallon is defined as 231 cubic inches. 1 cubic foot is 12 x 12 x 12 = 1728 cubic inches. 1728 divided by 231 = 7.4805, used as 7.48.
- One million gallons is 1000000 gallons. Definition of the word million. Exact.
- One day has 1440 minutes. 24 hours x 60 minutes = 1440 minutes. Exact.
Where this fits in the official exam
- The official subject list this module serves
- Twenty official Need-to-Know subject categories, from Statutes and Rules through Math Problems (incl. Permits, Design Criteria, Safety, Laboratory, Collection, Pumping, treatment stages, Process Control, Disinfection, Sludge Digestion, Biosolids, Effluent Disposal).
- Source: TCEQ Wastewater Operator Exam Knowledge ('What You Need to Know for a Class D Wastewater Treatment Plant Operator Exam' table.)