How do you arrive at the padding percentage values shown in this video?

Hamad,

There is a little bit of helpful information in this related post, also, I think.

Simply math. Now, if you're looking for a certain padding amount, that's all relative on how you want to design your site. But let's say you want 100 pixels of padding on one side. Now, let's say that your box's total width is 500 pixels. Just divide 500 pixels from 100 (500/100) to get .2, or 20 percent. You can check this by multiplying 500 by .2, and you'll get 100 pixels.

You can get more in depth with this by checking how much space you have in your browser (I recommend mobile first) and then do further math to get what you want, but quite frankly it's pretty simple (and I suck at math!) It will just take a bit of work and artistry.

Source: me. <--beginner.

There isn't necessarily a formula for the percentages, it's relative to the total width. So lets say you want 5% padding or 15% padding. It's how much of the width of the container would you like to use as padding.

Hope this helps

Kind of like Nathaniel said. You just have to look at the size of your box and figure out how much you think it needs. As long as you keep in mind the total width of your box and page, you should be good.