Water · Worked step by step
How many gallons are in 1,000 feet of 6 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 6 inches across and 1,000 feet long. How many gallons of water 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 = 6 in = 0.5 ft
- The pipe size is in inches, but everything else is in feet.
- 6 inches divided by 12 is 0.5 feet.
- Now all our lengths are in feet.
Quick trick: Always turn pipe inches into feet first. 6 in = 0.5 ft.
- 2
Find the circle end
area = 0.785 × 0.5 × 0.5 • area = 0.19625 sq ft
- The end of the pipe is a circle, so use 0.785 times across times across.
- 0.5 × 0.5 = 0.25.
- 0.25 × 0.785 = 0.19625 square feet.
- 3
Times length, then gallons
cubic feet = 0.19625 × 1,000 = 196.25 • gallons = 196.25 × 7.48 = 1,468
- Multiply the circle by the 1,000 foot length: 196.25 cubic feet.
- Then times 7.48 for gallons.
- That is about 1,468 gallons.
Quick trick: A pipe is just a round tank on its side; the length plays the part of depth.
Remember this for good
A pipe is a long round tank. Gallons = 0.785 times across times across, times the length, times 7.48.
Turn the inches into feet first (6 inches is 0.5 ft). Then it is the same round-tank math, just lying on its side: circle floor, times length, times 7.48.
Solve it fast next time
- Change the pipe size from inches to feet before anything else.
- Pipe gallons = 0.785 times across times across, times length, times 7.48.
- 6 inches is 0.5 ft, 12 inches is 1 ft; divide inches by 12 to get feet.
The answer: About 1,468 gallons.