I've heard this question many times from a Home owner with a small Chainsaw.
In my opinion there are many variables. Going way back, I have used a small Macllough Eager Beaver once and dropped a pretty big ole pine tree. Skill comes into play. How sharp is the chain. Is the bar oiling well, are you in a hurry? The Eager Beaver may have had a 14 inch bar, can't remember. I just gave away an old Poulan 2150. One time I had a 20 inch Oregon bar on that saw. It's 37cc if I recall. Then I remember the Sthil 024, 18 inch bar I think. Not fast but still cut some trees the bar barely reached past the center of the stump. The Sthil 026 came along and with a 20 inch bar dropped some big trees. Not real fast but got it done. The Poulan Pro 380 a 60cc saw pulled a long bar pretty good. Maybe 28inch bar. Details not sure. But the saw that seemed to be most handy was the Sthil 026 and or the small Poulan. After that the Sthil 440 walks through wood so fast there's no comparison. But the smaller saws can cut trees almost double their bar length in fairly skilled hands and better in professional hands but pros use pro saws and Pros don't ask this question. So, as I've said, there is no one size fits all answer if we consider skill. I'd be interested in hearing about the smallest saw anyone has used for the biggest tree they've dropped. Just curious.
In my opinion there are many variables. Going way back, I have used a small Macllough Eager Beaver once and dropped a pretty big ole pine tree. Skill comes into play. How sharp is the chain. Is the bar oiling well, are you in a hurry? The Eager Beaver may have had a 14 inch bar, can't remember. I just gave away an old Poulan 2150. One time I had a 20 inch Oregon bar on that saw. It's 37cc if I recall. Then I remember the Sthil 024, 18 inch bar I think. Not fast but still cut some trees the bar barely reached past the center of the stump. The Sthil 026 came along and with a 20 inch bar dropped some big trees. Not real fast but got it done. The Poulan Pro 380 a 60cc saw pulled a long bar pretty good. Maybe 28inch bar. Details not sure. But the saw that seemed to be most handy was the Sthil 026 and or the small Poulan. After that the Sthil 440 walks through wood so fast there's no comparison. But the smaller saws can cut trees almost double their bar length in fairly skilled hands and better in professional hands but pros use pro saws and Pros don't ask this question. So, as I've said, there is no one size fits all answer if we consider skill. I'd be interested in hearing about the smallest saw anyone has used for the biggest tree they've dropped. Just curious.