Ok. To convert anything into anything else you do something very very simple. Divide what you want...by what you have. For example, if I have 15 liters of water, I'm going to multiply by gallons over liters. Multiply the measurement given by what you want, then divide that by what you have.
You take the higher unit and make that 1, then however many of the other units you can fit and that's the other number. That can become 1 gallon / 3.79 liters, or 30m / 3000cm, etc.
So you have 15 liters, you want it in gallons, and it takes four gallons per liter:
15 liters x 1 / 3.79
= 4 gallons (3.9577836 gallons unrounded)
This works because you are dividing the measurement given by how many units of that measurement it takes to fit in another measurement. However, I prefer this method because it makes it easier to figure out when to multiply into smaller units, or divide to get bigger units.
How to convert: measurement x want / have
