Water and wastewater · Worked step by step
How much pressure is at the bottom of a 40 foot tank?
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 tank holds water 40 feet deep. Ignoring anything else, how much pressure is at the bottom?
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
Write what you know
depth = 40 feet • 1 foot = 0.433 psi
- The water is 40 feet deep.
- Every foot makes 0.433 psi.
- Multiply to get the pressure.
- 2
Multiply depth by 0.433
pressure = 40 × 0.433 • pressure = 17.3 psi
- 40 × 0.433.
- 40 × 0.4 is 16, plus a bit more.
- That gives about 17.3 psi at the bottom.
Quick trick: Quick estimate: 40 × 0.4 = 16, so the answer is just above 16.
Remember this for good
Each foot of water makes about 0.433 psi, so pressure is the depth in feet times 0.433.
Depth times 0.433. The deeper the water, the more it presses on the bottom, at 0.433 psi for every foot.
Solve it fast next time
- Feet given, psi wanted? Multiply by 0.433.
- The pressure number is always smaller than the feet number.
- Depth in feet is all you need for the pressure at the bottom.
The answer: About 17.3 psi.