Water and wastewater · Worked step by step
How much pressure does 92 feet of water make?
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 storage tank's water sits 92 feet above a house. Ignoring friction, how much water pressure does that height make at the house?
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 down what you know
height = 92 feet • 1 foot of water = 0.433 psi
- Don't solve anything yet. First just write what you were given.
- The water is 92 feet tall. That is our height.
- And here is the one fact you need: every 1 foot of water makes about 0.433 psi. Keep that number close.
Quick trick: On the real exam, 0.433 is printed on your formula sheet. You don't memorize it, you just know when to grab it.
- 2
Decide what to do with the numbers
pressure = 92 × 0.433
- We want pressure. We have 92 feet, and 0.433 psi for each foot.
- If one foot gives 0.433, then 92 feet gives 92 of those.
- "92 of" something means multiply. So pressure = 92 × 0.433.
Quick trick: Whenever you read "for each" or "per", that is your signal to multiply.
- 3
Do the multiplication
pressure = 39.8 psi
- Now just multiply: 92 × 0.433.
- 92 × 0.4 is about 36.8, and the little bit extra brings it to 39.8.
- So the pressure is about 39.8 psi. That is answer a.
Quick trick: No calculator in your head? Round: 92 × 0.4 is about 37. The real answer sits just above 37, so pick 39.8.
Remember this for good
Every 1 foot of water pushes down about 0.433 psi. So height in feet times 0.433 gives you pressure in psi.
Picture a tall glass of water. The taller the water, the harder it presses on the bottom. One foot of water presses with 0.433 psi. Stack 92 feet and it presses 92 times as hard.
Solve it fast next time
- Feet given, psi wanted? Multiply by 0.433.
- Psi given, feet wanted? Go the other way: multiply by 2.31.
- Gut check: the psi answer is always SMALLER than the feet number, because 0.433 is less than 1.
The answer: About 39.8 psi.