Have you ever wanted to create an attractively spaced stripe, or tried to calculate how long an item should be once you've gotten the width figured out? If so, you've come to the right place.
There are three mathematical concepts I've found extremely helpful when designing a new pattern. Don't let the math part scare you off.
They're called Fibonacci numbers, Lucas numbers and the Golden Ratio. The Golden Ratio is also called phi. They're closely related, particularly Fibonacci numbers and the Golden Ratio. Never fear, I won't get into all the gory details here. That would assume I fully understand it all myself. :)
Here are the first few Fibonacci and Lucas numbers and the Golden Ratio. Follow the appropriate link for a short explanation and examples of how to use each of them.
So, why use these particular numbers? Essentially, a pattern or proportion that's based on them will appear more attractive to the human eye than one that's not. This is partially true because they're quite common in nature.