How Many Top-Level Folders Should You Have In Your Digital Folder Hierarchy To Optimize Efficiency & Effectiveness?

A good folder structure for personal knowledge and digital artifacts eases everyday life. Things can be neatly stored, quickly and reliably found, and sustainably organized.

To design a good folder structure, one should emphasize the topmost layer, the so-called root level. Since we always enter our hierarchy from the top when we navigate, the number of folders on this top level basically encodes a certain divide-and-conquer strategy. For instance, having three instead of two root-level folders makes the first navigation step more powerful, as it immediately brings us to the correct third (instead of half) of our knowledge base. The same goes for moving from three to four categories and beyond.

To denote this somewhat special function, we call top-level folders in our hierarchy its organizational spaces. The folders located directly within these spaces — on the second level — are also given a special name — organizational containers — to distinguish them from everything below, which we just call “folders.” Based on the same reasoning as with spaces, containers can improve hierarchy navigation if the second layer is still mainly used for navigation and contains few actual files.

From this, we can say that for navigation purposes, more categories lead to better divide-and-conquer strategies, making each navigation step more powerful. However, this insight must be qualified as various factors cap it.

One of these factors concerns our cognitive setups. There's a ceiling to how many things we can consider at once, some kind of mental WIP limit. This impacts how glanceable our folder structure is and implies that when one reaches a certain number of org spaces, it will get harder to make that first navigation decision. The best guess at how many folders we can juggle in our minds is somewhere between 4 and 9.¹ Anything below that wastes potential and anything above that weakens our divide-and-conquer strategy as (oversimplified) we can say that categories now must repeatedly be “loaded and unloaded” into/from memory.²

However, even for individuals with a high cognitive limit or those who rarely navigate with folders and use other means of accessing their files, increasing the number of organizational spaces is problematic because it reduces clarity. From centuries of philosophizing, we can say with relative certainty that perfect semantic categorization is impossible. From this, we can conclude that with every additional top-level folder, we incur a small incongruency, and drawing exact boundaries and maintaining a clear separation between categories gets harder. That is, with every additional folder we increase the chance of misplacing stuff. So, from this perspective, reducing the number of organizational spaces to the absolute minimum is best.

Taken together, up to a certain limit, additional spaces reduce the amount of navigation needed to reach a destination, but above that limit, we see diminishing returns due to added cognitive costs as well as blurred boundaries. These two opposing forces that determine the “optimal” number of organizational spaces. It is thus reasonable to adopt the following heuristics to support a strong divide-and-conquer strategy:

• The top level of our folder hierarchy should contain 4-8 folders and no files beyond that, as files must be counted toward the total number of items.

• Any layer mainly used for navigation should be structured similarly. If not, other means are used to ensure glanceability.

Note, however, that it is probably best to prioritize clarity over efficiency. For instance, it is better to have 5 crips than 8 semi-crisp categories; one should fall back on fewer categories.

Note that these heuristics are mainly meant to ease navigation; they pertain to hierarchy layers that contain mostly folders. Once one gets down to the deeper levels, and the aim is to make finding files easier, one should choose a different strategy. Research indicated that it is around 21 items that introducing subfolders is becoming more efficient.³ On file instead of folder level, it may thus be better for efficiency reasons to grow in breadth before growing in depth to a certain point. With this, we can add one final heuristic:

• Each folder that contains mostly files should grow in breadth until 21 items are reached before growing deeper with sub-folders, as this optimizes scanning.

Knowledge Builders — a Fractal Productivity spin-off — will build up towards a novel org method called PEAKER which tries to follow these heuristics. With PEAKER we end up with 6-8 org spaces.

1. Based on one of the most cited psychology papers of all time, we can rely on Miller’s Number as a rough estimate. Miller found that in certain cases, our cognitive limits are around 7 ± 2 items. This number was later downregulated to 4 ± 2. Yet, familiarity may have an impact, so if we navigate the same org spaces multiple times per day, for many months, it may be reasonable to assume that we can take the prior number (7 ± 2) as a more accurate guidance for folder hierarchies. The ± 2 in Miller’s number hints at the big difference in individuals’ mental capacities. So, some individuals may get away with 9 spaces while others do best with as little as 4. See The Magical Number Seven, Plus or Minus Two (Wikipedia) for more on this.

2. The effect may be unnoticeable for a singular journey towards a certain file as it may only add a second or two. Yet, the more frequently one navigates an organizational structure, the more impact this minute detail has. Over a lifetime, this minor cognitive cost can add up.

3. Bergman, O., Whittaker, S., Sanderson, et al. (2010). The effect of folder structure on personal file navigation. Journal of the American Society for Information Science and Technology, 61(12), 2426–2441.