Water · Worked step by step
How many gallons are in a 12 foot round tank, 10 feet deep?
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 round tank is 12 feet across and holds water 10 feet deep. How many gallons does it hold?
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
Find the circle floor
area = 0.785 × 12 × 12 • area = 113.04 sq ft
- The floor is a circle, so use 0.785 times across times across.
- 12 × 12 = 144.
- 144 × 0.785 = 113.04 square feet.
Quick trick: 0.785 times a number times itself gives a round floor every time.
- 2
Stack it up by the depth
cubic feet = 113.04 × 10 • cubic feet = 1,130.4
- Multiply the floor by the 10 foot depth.
- 113.04 × 10 = 1,130.4 cubic feet.
- One step from gallons.
- 3
Turn cubic feet into gallons
gallons = 1,130.4 × 7.48 • gallons = 8,455
- Multiply cubic feet by 7.48.
- 1,130.4 × 7.48 is about 8,455 gallons.
- That is your answer.
Quick trick: Estimate: 1,130 × 7.5 is about 8,475. The real answer sits right there.
Remember this for good
Round tank gallons: 0.785 times across times across for the floor, times depth for cubic feet, times 7.48 for gallons.
Every round tank is the same three moves: circle floor (0.785), stack it up (depth), turn into gallons (7.48). The numbers change, the moves do not.
Solve it fast next time
- Round tank = 0.785 times across times across, then times depth, then times 7.48.
- Across is the diameter. Do not cut it in half here.
- Same finish as any volume problem: cubic feet, then gallons.
The answer: About 8,455 gallons.