Water and wastewater · Worked step by step
How much does 500 gallons of water weigh?
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
How much does 500 gallons of water weigh, in pounds?
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
gallons = 500 • 1 gallon = 8.34 lb
- We have 500 gallons of water.
- Each gallon weighs 8.34 pounds.
- So we just need 500 of those.
Quick trick: Water is heavy: about 8.34 pounds a gallon. That is why a full tank weighs so much.
- 2
Multiply gallons by 8.34
weight = 500 × 8.34 • weight = 4,170 lb
- 500 of something that weighs 8.34 each means 500 × 8.34.
- 500 × 8 = 4,000, and 500 × 0.34 = 170.
- Add them: 4,000 + 170 = 4,170 pounds.
Quick trick: Split 8.34 into 8 and 0.34, multiply each by 500, then add. Easier than one big multiply.
Remember this for good
One gallon of water weighs 8.34 pounds. So gallons × 8.34 gives the weight in pounds.
8.34 is the magic water number: the weight of one gallon. It is the same 8.34 you use in the pounds-per-day chemical formula. Learn it once, and it pays off everywhere.
Solve it fast next time
- Weight of water = gallons × 8.34.
- This is the same 8.34 as the pounds formula (flow × dose × 8.34). One number, two uses.
- Rough check: 8.34 is a bit over 8, so the weight is a bit over 8 times the gallons.
The answer: 4,170 pounds.