The estimate covers materials only. Sealant, screws, gutter guards, splash blocks, fascia repairs and labour are extra.
How the gutter calculator works
GutterCalc multiplies the drainage area (gutter length × roof depth) by the pitch factor and the rainfall intensity, then picks the smallest gutter of your style whose capacity is at least that adjusted area. Downspouts = the larger of the gutter length ÷ the maximum run per downspout and the roof area ÷ the downspout capacity, rounded up. Hangers = length ÷ spacing + 1. Slope = ¼ inch (or your figure) per 10 feet over the run to each downspout.
Gutter capacity (adjusted sq ft)
| Gutter | Capacity |
|---|---|
| 5″ K-style | 5,520 |
| 6″ K-style | 7,960 |
| 5″ half-round | 2,500 |
| 6″ half-round | 3,840 |
Pitch factor
| Roof pitch | Factor |
|---|---|
| Flat to 3/12 | 1 |
| 4/12 – 5/12 | 1.05 |
| 6/12 – 8/12 | 1.1 |
| 9/12 – 11/12 | 1.2 |
| 12/12 and steeper | 1.3 |
Downspout capacity (rule of thumb)
| Downspout | Opening | Roof area |
|---|---|---|
| 2 × 3″ rectangular | 6 sq in | ≈ 600 sq ft |
| 3 × 4″ rectangular | 12 sq in | ≈ 1,200 sq ft |
| 3″ round | 7.1 sq in | ≈ 700 sq ft |
| 4″ round | 12.6 sq in | ≈ 1,250 sq ft |
Capacities, pitch factors and the 1 sq in per 100 sq ft downspout rule are widely published rules of thumb for residential gutters, not a code calculation; local codes (for example the plumbing code's storm drainage tables) and your installer may size differently. Results are estimates.
Frequently asked questions
Does this include installation?
No, materials only.
Are seamless gutters priced the same way?
Seamless gutters are usually priced per foot installed. Enter that price per foot and set the other prices to what is not included.
What costs the most?
The gutter itself, then hangers and downspouts.
Is GutterCalc free?
Yes, with no sign-up or ads.
Are my measurements saved?
Yes, in this browser only.