The principle of 8pt Grid is that use multiples of 8 (8, 16, 24, 32, 40, 48, 56, etc.) to layout, dimensions, padding, and margin of elements.

Related Articles:
https://medium.com/swlh/the-comprehensive-8pt-grid-guide-aa16ff402179
https://medium.com/built-to-adapt/intro-to-the-8-point-grid-system-d2573cde8632
https://blog.prototypr.io/the-8pt-grid-consistent-spacing-in-ui-design-with-sketch-577e4f0fd520