In theory:
- Under 10 is very easy
- 10-19 is easy
- 20-29 is medium difficulty
- 30-39 is hard
- 40+ is very hard
But those metrics are very flawed. Look at these two real keywords from a recent KW research project (details redacted/changed):
- can [website] detect screenshots
- Search volume: 0
- 163,000 results shown when searched in Google
- intitle: 0
- inurl: 0
- Keyword competition score: 27
- buy [service]
- Search volume: 590
- 9,530,000 results shown when searched in Google
- intitle: 26,400
- inurl: 26,600
- Keyword competition score: 27
Exact same keyword competition score.
That first keyword is definitely very easy. You could shit out a spun blog post with okay-ish onpage optimization and it would probably rank on the first page with no offpage linkbuilding at all. That second one is definitely hard, possibly even very hard. Even with great onpage optimization, you'd be lucky to break the top 30 without any link building.
KW competition values can be useful at a glance to get organized and to help weed out certain keywords. Once you've narrowed down your possible keywords to a smaller pool, it becomes basically worthless, especially when you're looking at individual keywords.