I’d suggest maybe a bit different approach to the grid where it requires less math and easier to modify. In your demo, if you want to change the padding/margin, you’ll also have to adjust the widths of the columns which can be a real pain.
In this demo, all you have to do is change the padding on .col to separate each module and change the padding on the article which results in much easier to maintain grids. Hopefully you find this helpful. Grid Demo