How would you weigh an elephant without using a scale?

If we are not allowed to use a scale then what are our options? Well, there aren’t very many.

It helps to think of natural things of which we already know the properties of. Let’s think of water – that’s something natural that has a lot of measurable properties.

What could we do with water?

Well, we do know that one of the properties of water is that it weighs 1 kg. per liter, or 8.34 lbs per gallon. How can we use this knowledge to our advantage to solve this problem?

Put the elephant in a tank

What if we put the elephant on a big raft inside a full tank of water?

What we could do then is measure the volume of water that’s displaced and that would give us a great approximation of the weight of the elephant.

So, say that 7500 liters (or about 1,900 gallons) of water is displaced, then that means the elephant weighs about 7500 kilograms, or 16,500 pounds.