Water · Worked step by step
How many gallons are in 2,000 feet of 8 inch main?
If math has never been your thing, you are in the right place. Try it on paper first, then we write it out with you, one small step at a time, and explain every step in plain words so you never lose the thread.
The problem
A water main is 8 inches across and 2,000 feet long. How many gallons does it hold when full?
Grab a pen and paper first
Give it a real try on paper before you watch. If you get stuck, take a hint. If you go blank, that is fine, press play and we will walk it through together.
Watch it solved, with you
Every step is written out slowly and explained in plain words, so you always know what just happened. Nobody skips ahead and leaves you behind.
Press play and I’ll write it out with you, one small step at a time.
Every step gets a plain-words explanation here, so you always know exactly what just happened and why.
The written version, step by step
- 1
Change inches to feet
across = 8 in = 0.667 ft
- 8 divided by 12 is 0.667 feet.
- Keep three decimals so the answer stays accurate.
- Now all in feet.
Quick trick: 8 inches is two-thirds of a foot, 0.667.
- 2
Find the circle end
area = 0.785 × 0.667 × 0.667 • area = 0.349 sq ft
- 0.667 times 0.667 is 0.445.
- 0.445 times 0.785 is 0.349 square feet.
- That is the pipe's opening.
- 3
Times length, then gallons
cubic feet = 0.349 × 2,000 = 698 • gallons = 698 × 7.48 = 5,225
- Multiply by the 2,000 foot length: about 698 cubic feet.
- Then times 7.48 for gallons.
- About 5,225 gallons.
Remember this for good
An 8-inch main is 0.667 feet across (8 divided by 12). Then it is the usual pipe math: circle end, times length, times 7.48.
8 inches divided by 12 is 0.667 feet. Keep three decimals; rounding it to 0.7 too early makes the answer drift.
Solve it fast next time
- Change 8 inches to feet: 8 divided by 12 is 0.667 ft.
- Pipe gallons = 0.785 times across times across, times length, times 7.48.
- Keep a few decimals on 0.667 so the answer stays accurate.
The answer: About 5,225 gallons.