One roof, four answers: the gutter calculator sizes the system from your rainfall, the BOM panel counts every elbow and hanger, the hydraulic check verifies the flow, and the shopping list turns it all into a purchase-ready checklist. Every formula is printed on the page and every result updates live.
Most “gutter calculators” online answer one question and stop: enter your square footage, receive a profile letter. But a gutter system is a chain — the roof sheds water at a rate set by area, pitch, and rainfall; the gutter carries it at a rate set by profile and slope; the downspouts discharge it at a rate set by open area; and the whole assembly hangs on fastening spaced for a climate the calculator on those sites never asked about. Break any link and the result is the same: overflow at the first real storm.
So this toolset answers the chain, not the link. The sizing engine produces the smallest standard profile that clears your design storm — and because it sizes each run separately, it will happily return four different answers for a hip roof instead of pretending one number fits all four eaves. The BOM counts the fittings that a gutter-and-a-prayer purchase always forgets. The hydraulic check verifies the system the tables might have missed. The shopping list closes the loop at the supply house.
Everything runs in your browser, on your device, on every keystroke. No account, no email gate, no PDF behind a paywall — the calculators are the product, and they are free.
A system, not a single numberPhoto: UnsplashWhat “free” means here
No pro tier, no watermarked exports, no results held behind a signup. The site is funded by clearly separated advertising — the calculators themselves are never the thing being sold.
Four tools, one workflow. Each one takes the previous answer as its input — which is why they live on the same page, and why the numbers never need re-typing.
The flagship tool. Enter roof footprint, pitch, and local design rainfall to get the smallest standard gutter that clears the storm — K-style or half-round, 4" through 6" — plus the downspout count, size, and spacing that keep every run drained, and the total linear footage to buy. Run splitting sizes a hip roof run by run instead of as one giant number, and the near-limit flag warns when your load lands within 10% of a profile's rated ceiling.
Open the Gutter CalculatorBeyond sizing: elbows, outlet tubes, end caps, inside and outside miters, hidden hangers, and downspout straps — counted from your corners, eave height, wall offset, and ground extension. Hanger and strap spacing tightens automatically for your climate zone: 24" on center in standard regions, down to 12" in extreme snow country and 16" with 4-ft strapping in the Florida HVHZ. The fitting count is what separates a real bid from a gutter-and-a-prayer.
See the BOM PanelA SMACNA-style verification pass that checks storm flow directly: required flow in gpm equals design area × intensity × 0.0104, cross-checked against the gutter's cross-section and the downspouts' total open area — the same ~100 sq ft per in² rule the capacity tables use, applied to your real numbers instead of a lookup row. Vertical high-wall area from IPC 1106 folds in before the check, and custom gutter profiles get the proportion rule so nothing slips through because it wasn't in the table.
Check the HydraulicsEvery result converts to a purchase-ready checklist in standard sizes — 10-ft gutter sections sliced from your runs, downspout lengths from eave height to grade, elbows, hangers, straps, and sealant — with a waste factor already applied (10% on sectional, 4% on seamless) and a one-tap PDF export for the supplier or contractor. Tick items off while you load the cart; the list persists between visits.
Build the List
One roof, four answersPhoto: UnsplashWhy the order matters
Sizing answers "will it carry the storm?"; the BOM answers "what do I buy?"; the hydraulic check catches the cases lookup tables miss — tall walls, custom profiles, long runs. A system can pass one check and fail another.
A real gutter project moves through the toolset in the same order the questions arrive — each step hands its output to the next as an input, which is why the results never need to be re-typed or re-interpreted.
Enter the roof footprint, pitch, and design rainfall. The calculator applies the pitch factor, splits the load across runs, and returns the smallest standard profile that clears the storm plus the downspout count, size, and spacing that keep it drained.
Corner counts, eave height, wall offset, and ground extension become elbows, miters, straps, and hangers — with spacing tightened for your snow or hurricane zone before the list is printed.
Storm flow against cross-section and open area — including vertical wall area and custom gutter proportions — so edge cases surface before the first storm, not during it.
Everything converts to a checkable shopping list in standard sizes with a waste factor applied, exportable as a PDF for the supplier or contractor — and it persists between visits while you shop.
Visitors arrive with different jobs: planning a system, verifying a quote, or turning a plan into a purchase. These are the categories that match — pick the one that sounds like you.
Category 01 · Plan & Size
The upstream decisions: how big the gutter must be, where the spouts land, and whether the roofline forces a special case. Get these right and everything downstream is arithmetic; get them wrong and no amount of good installation rescues the run.
Category 02 · Verify & Comply
The verification decisions: does the proposed system actually carry the storm, does the fastening match the climate, and does the number in the bid match the number the math produces. This is where planning estimates earn their keep.
Category 03 · Buy & Install
The downstream decisions: how many sections, which fittings, how much overage, and what the truck needs to carry. A perfectly sized system still stalls in the yard if the list was never real.
Every tool and reference section on the site — each one narrow, deep, and built on the same published data as the flagship gutter calculator.
Profile, spouts, spacing, footage — live on every keystroke.
Fittings and fastening schedule from your roofline.
The published data, rescaled to your rainfall.
Buy-ready checklist with PDF export.
The system drawn to scale, slope included.
A real house sized by hand, line by line.
The questions homeowners ask before buying.
The reading that explains why each number moves.
How the tools run, which standards the data follows, and how the workflow fits together.
Enter the roof, pick your rainfall, and watch the size, downspout layout, accessory list, and cost line up in real time — then carry the PDF to the counter and buy once.