Gutter Calculator
Work out exactly how much gutter, how many hangers and how many downspout elbows you need from your roofline runs, with the standard waste allowance already built in. Add your own prices for a full cost estimate — nothing here uses a stale national average.
How this calculator works
The calculator adds up every roofline run, applies a 10% waste allowance for seams, corners and end caps, then uses that total to work out hangers and elbows:
total_gutter_ft = sum(runs) × 1.10 hangers = ceil(total_gutter_ft × 12 / hanger_spacing_in) downspout_elbows = downspout_count × 2
Downspout count is entered manually rather than calculated, since it depends on corner placement and local drainage needs as much as raw footage — the guidance text above the field gives a sensible starting point.
Worked example
A house with a 40 ft front run, 40 ft back run, and 20 ft runs on each side, standard 24 in hanger spacing:
- Roofline total: 40 + 40 + 20 + 20 = 120 ft.
- Add 10% waste: 120 × 1.10 = 132 ft of gutter to buy.
- Hangers: ceil(132 × 12 ÷ 24) = 66 hangers.
- At one downspout per 35–40 ft, 132 ft points to about 4 downspouts, entered manually.
- Elbows: 4 × 2 = 8 elbows.
With a $7/ft installed gutter price, $85 per downspout, $2.50 per hanger and $12 per elbow, that example totals roughly $1,525 — itemized in the cost panel above as soon as prices are entered.
Choosing gutter size and profile
| Choice | Effect | Why |
|---|---|---|
| 5 in vs 6 in | Price + capacity | Larger size sheds more water, doesn't change linear footage |
| K-style vs half-round | Price + look | Profile shape only, no effect on the footage calc |
| Hanger spacing | Hanger count | Tighter spacing means more hangers per foot |
None of these choices change the total gutter footage you need — that figure is fixed by your roofline. They only change the price per foot and, for hanger spacing, how many hangers that footage requires.
Measuring your roofline
Enter one run per continuous stretch of gutter, measured along the fascia:
- Straight sides — measure eave to eave along the fascia board, not the roof slope.
- Corners — treat each side of the house as its own run rather than one continuous total.
- Dormers and additions — add a separate run for each roofline that needs its own gutter.
- Valleys and low points — these usually need an extra downspout nearby regardless of overall footage.
How much does a new gutter system cost?
Rather than quoting a national average that's stale the day it's published, this calculator prices the job from what you actually enter. Give a gutter price per linear foot, plus what you'll pay per downspout, hanger and elbow — each is itemized and totaled. The estimate assumes standard hidden hangers and doesn't include fascia repair, leaf guards, or removal of an existing system.
Frequently asked questions
5-inch vs 6-inch gutters — when is the larger size needed?
5-inch K-style gutters handle most residential roofs and are the standard choice. 6-inch gutters carry roughly 40% more water and are worth it on steep or large roof planes, in heavy-rainfall areas, or where long runs feed a single downspout. It changes price and capacity, not the linear footage calculation.
How many downspouts does an average house need?
A common rule is one downspout per 35–40 ft of gutter run, or one per corner, whichever gives more coverage. Most single-story homes end up with four to six downspouts total, more in heavy-rainfall areas.
What's standard hanger spacing?
Hidden hangers are typically spaced every 24 inches on standard installs. In regions with heavy snow and ice load, tightening to 16–18 inches gives the gutter more support against the extra weight.
K-style vs half-round — does it change the linear footage calc?
No. Profile shape only affects price per foot and appearance. The linear footage needed is driven entirely by your roofline runs plus the waste allowance, regardless of profile.