| Gutter runs | 4, about 30 ft each |
|---|---|
| Slope | ¼" per 10 ft toward the downspout: 0.75" drop per run |
| End caps | 8 |
| Downspout outlets | 4 |
| Downspout pipe | 4 10 ft sections |
| Elbows | 12 (3 per downspout: 2 at the eave, 1 at the bottom) |
That's the minimum: one downspout per run, plus a common rule of thumb of at least one per 40 ft of gutter (from Amerimax's vinyl guide). Check each long run on its own, and add downspouts where a big or steep roof drains into one run.