How wide should side navigation be?
Width and Height of the Sidebar
A width between 20% and 40% is usually the best choice for a single sidebar and if you're going to use more than one sidebar, I suggest you don't exceed a total width of 50% (20% + 20% and 15% + 35%, for example).
What is sidebar navigation?
Sidebars are a staple of website navigation — they're convenient to users and ensure that certain page elements are always in view. Inside them, you can place links, menus, widgets, CTAs, display ads, or just about anything else you want.