Gutter Calculator
Estimate gutter linear feet, sections, downspouts, hangers and material cost from your roofline measurements.
Gutter length, sections, downspouts, and hangers
Your measurements stay in this browser. This is a planning estimate, not a code-approved design.
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Quick answer
To calculate how much gutter you need, add the linear feet of every roof eave that receives gutters. Add your chosen waste and cut allowance, then divide each run by the stock gutter section length and round up. An 80 ft run at 10% waste is 88 ft to order and 9 sections of 10 ft.
How many downspouts do I need?
A planning rule of thumb is one downspout about every 20 to 40 ft of gutter, counted on each run so a long run does not hide behind a short one. At the default 35 ft spacing, 160 ft plans 5 downspouts and 100 ft plans 3. The real count also depends on roof catchment, rainfall, outlet size, and local requirements. It is not a code minimum by itself.
How Much Gutter Do I Need?
Measure the eave runs that actually drain into a gutter. A gable roof usually has two of those runs. The gable ends are rakes, and they are not guttered just because they are part of the wall. A hip roof can be guttered on all four sides. A shed roof usually drains to one low side. Adding the building perimeter is right only when every side receives a gutter.
Add the runs to get the measured gutter length. Then add waste to each run and round that run up to whole stock sections. Two separate 40 ft runs at 0% waste and 10 ft sections need 4 sections each, 8 total. The same two runs at 10% waste need 10 sections, while one combined 80 ft run at 10% waste needs only 9. Separate runs waste a partial section that a single long run would have used.
House floor area is a different number. If you only know the footprint, start with length and width and the roof style above, then confirm the eaves on site. To calculate roof area, use the roof area calculator. That area is for roofing materials, not for gutter linear feet.
How Many Downspouts Do I Need?
Water has to leave the gutter before the run overflows. A common residential planning range is an outlet every 20 to 40 ft. This page uses max(1, ceil(run ÷ spacing)) on each run, with 35 ft as the editable default. A 120 ft run at that spacing plans 4 downspouts. Two short runs can need more outlets than one long run of the same total, because each run needs its own discharge.
Spacing does not know how much roof is dumping into that gutter, how hard it rains, or whether the outlet is a 2x3 or a 3x4 downspout. A large or steep catchment, a long run, or a heavy local storm can need closer outlets or a larger downspout even when the spacing rule looks fine. Enter the projected catchment and a local rainfall intensity in the sizing section, then compare the flow with the manufacturer’s rated capacity.
What Size Gutters Do I Need?
Five-inch K-style gutter is a common residential choice. Six-inch gutter is often considered for a larger catchment, a longer run, or heavier rainfall. Half-round gutter is a different profile, so it does not share a K-style capacity. Downspout size is a separate choice: a 2x3 downspout and a 3x4 downspout do not carry the same flow, and a larger gutter still overflows if the outlet is too small or too far away.
Gutter and downspout sizing depends on roof catchment, rainfall intensity, gutter profile, slope, outlet arrangement, local code and manufacturer specifications. Use this calculator for planning and verify the final system against local requirements. SMACNA’s Architectural Sheet Metal Manual and applicable International Plumbing Code storm-drainage provisions describe methods for that check. U.S. rainfall intensity comes from NOAA precipitation-frequency data for the site, not from one nationwide number.
For a planning flow, Q ≈ A × i × C × 0.0104 gallons per minute when A is projected catchment in square feet, i is rainfall in inches per hour, and C is a runoff coefficient. Do not multiply the roof footprint by a pitch factor and call that the drainage area. Sloped surface area is what you use when you calculate roof pitch and then estimate roofing. Pitch can still matter because a steep roof may throw water past the gutter, but that is a planning assumption, not a second area.
5-Inch vs 6-Inch Gutters
| Comparison | 5-inch | 6-inch |
|---|---|---|
| Common use | Smaller homes and shorter eaves | Larger catchments and longer runs |
| Relative capacity | Lower for the same profile and slope | Higher for the same profile and slope |
| Typical residential use | A frequent K-style choice | Used when 5-inch is likely to be tight |
| Large or steep roofs | Easier to overrun | More often considered |
| Heavy rainfall | Needs closer outlets or a capacity check | Still needs a capacity check |
| Compatibility | Match hangers, corners, and outlets to 5-inch | Match fittings and outlets to 6-inch |
| Cost | Usually less gutter stock and fittings | Usually more stock and fittings |
How to Measure for Gutters
- Identify guttered eaves. Mark only the roof edges that drain into a gutter. Skip gable rakes and any wall with no gutter.
- Measure each run. Measure the length of each eave along the fascia, in feet or meters.
- Record separate runs. Keep each run on its own line. Do not add them into one number before you round stock sections.
- Measure corners. Count inside corners and outside corners. They are fittings, not extra gutter length.
- Record downspout positions. Note where leaders can discharge, and the drop from the gutter to the ground or extension.
- Check stock section length. Use the length your supplier sells, often 10 ft and sometimes 12 ft.
- Add a cut and waste allowance. Add a percentage for cuts, corners, and damaged pieces, then round each run up to whole sections.
If the fascia board behind the gutter is being replaced, calculate fascia length separately. Fascia follows eaves and rakes. Gutter follows only the draining eaves. To estimate soffit area, use eave length and the overhang depth. Soffit area is not a gutter quantity.
Gutter Calculator Formula
- Total gutter run = sum of the gutter runs.
- Adjusted order length = each run × (1 + waste% ÷ 100), then added together.
- Sections for a run = ceil(adjusted run ÷ stock section length).
- Planning downspouts for a run = max(1, ceil(run ÷ spacing)).
- Hangers for a run = ceil(measured run ÷ hanger spacing) + 1.
- Downspout linear feet = downspout count × average drop, when a height is entered.
- Material cost = your prices × those quantities. Blank prices are skipped.
- Planning runoff, U.S. units: Q ≈ A × i × C × 0.0104 gallons per minute.
Worked Gutter Calculator Examples
80 ft run, 10% waste, 10 ft sections
Inputs. One 80 ft gutter run, 10 ft stock, 10% waste.
Calculation. 80 × 1.10 = 88. ceil(88 ÷ 10) = 9.
Result. 88 ft to order and 9 sections.
Why. The extra 8 ft does not fill a tenth section, so the order rounds up from 8.8 sections to 9.
Two 40 ft runs
Inputs. Two separate 40 ft runs and 10 ft sections.
Calculation. At 0% waste, each run is ceil(40 ÷ 10) = 4. At 10% waste, each run is ceil(44 ÷ 10) = 5.
Result. 8 sections with no waste, or 10 sections with 10% waste.
Why. One 80 ft run at 10% waste is 9 sections. Splitting it into two runs makes 10, because each run rounds up.
160 ft run and 35 ft downspout spacing
Inputs. One 160 ft run, 10 ft sections, 10% waste, 35 ft spacing, 3 ft hangers.
Calculation. 160 × 1.10 = 176, and ceil(176 ÷ 10) = 18. ceil(160 ÷ 35) = 5. ceil(160 ÷ 3) + 1 = 55.
Result. 18 sections, 5 planning downspouts, and 55 hangers.
Why. The downspout count is a spacing estimate for that run. It does not prove the outlets can carry the roof.
40 × 50 hip roof
Inputs. Building length 40 ft, width 50 ft, hip roof, every side guttered.
Calculation. Runs are 40 + 50 + 40 + 50.
Result. 180 ft measured. A gable with eaves along the 40 ft sides is 80 ft, not 180.
Why. Hip and gable do not share a gutter length. Use the hip perimeter only when all four edges are guttered.
Common Gutter Calculation Mistakes
- Measuring the entire perimeter when the gable ends have no gutter.
- Adding separate roof runs into one length before rounding stock sections.
- Ignoring the stock section length and ordering only the measured feet.
- Forgetting corners, outlets, and end caps, or assuming every system has exactly two end caps.
- Using too few downspouts on a long run because the spacing was never checked per run.
- Treating gutter size and downspout size as the same decision.
- Using sloped roof surface area as the drainage area instead of the projected catchment.
- Ignoring local rainfall and using a rainfall number from somewhere else.
- Treating this estimate as a code-approved design.
Gutter Size Quick Reference
10 ft sections for one run
| Gutter run | 10 ft sections | 5% buffer | 10% buffer |
|---|---|---|---|
| 40 ft | 4 | 5 | 5 |
| 60 ft | 6 | 7 | 7 |
| 80 ft | 8 | 9 | 9 |
| 100 ft | 10 | 11 | 11 |
| 120 ft | 12 | 13 | 14 |
| 160 ft | 16 | 17 | 18 |
| 200 ft | 20 | 21 | 22 |
Downspout spacing
| Run | 20 ft | 30 ft | 35 ft | 40 ft |
|---|---|---|---|---|
| 40 ft | 2 | 2 | 2 | 1 |
| 80 ft | 4 | 3 | 3 | 2 |
| 100 ft | 5 | 4 | 3 | 3 |
| 120 ft | 6 | 4 | 4 | 3 |
| 160 ft | 8 | 6 | 5 | 4 |
FAQ
What is a gutter calculator?
A gutter calculator turns measured eave runs into an order quantity: linear feet, stock sections, a planning downspout count, hangers, and optional material cost. It is a takeoff tool. It is not a substitute for the gutter manufacturer’s capacity chart or local code.
How do I calculate gutter linear feet?
Add the length of every eave that will receive a gutter. That sum is the measured gutter run. Multiply each run by 1 plus your waste percentage, then divide by the stock section length and round up. An 80 ft run with 10% waste and 10 ft sections is 88 ft to order and 9 sections.
How much gutter do I need for a 1,500 sq ft house?
Floor area does not set gutter length. A one-story 30 by 50 ft footprint is about 1,500 sq ft, but the gutter follows the eaves. A gable with eaves on the 50 ft sides is 100 ft of gutter. A hip roof with gutters on every side is the 160 ft perimeter. Measure the eaves that actually drain.
How much gutter do I need for a 2,000 sq ft house?
A 40 by 50 ft footprint is about 2,000 sq ft, and that still is not the gutter length. If the roof is a hip and every side is guttered, the four runs add to 180 ft. If it is a gable with eaves along the 40 ft sides, the two eaves add to 80 ft. The gable ends are rakes and are not guttered.
How many downspouts do I need?
A common planning rule is one outlet about every 20 to 40 ft of gutter, counted on each run. This page defaults to 35 ft, so a single 160 ft run plans 5 downspouts. Long runs, large catchments, and heavy rain need more outlets or larger outlets. Confirm the layout against rainfall, roof area, and the product’s capacity.
How many downspouts do I need for 100 feet of gutter?
At a 35 ft planning spacing, one 100 ft run estimates 3 downspouts. At 40 ft spacing the same run estimates 3, and at 20 ft spacing it estimates 5. That is a spacing rule of thumb for a single run, not a code count, and it ignores how much roof drains to that gutter.
Are 5-inch or 6-inch gutters better?
Five-inch K-style gutter is a common choice on smaller residential eaves. Six-inch gutter is often considered when the catchment is larger, the run is long, or local rainfall is heavy. Neither size has one capacity that fits every profile and slope. Use the manufacturer’s rating, and match the downspout size to the gutter rather than treating them as the same part.
How many 10-foot gutter sections do I need?
Divide each run, after waste, by 10 and round up, then add the runs. One 80 ft run at 10% waste needs 9 sections. Two separate 40 ft runs at 0% waste need 4 sections each, 8 total. The same two runs at 10% waste need 5 sections each, 10 total, because each run rounds up on its own.
How much waste should I add for gutters?
Many orders use about 5% to 10% for cuts, corners, and a damaged stick. Straight runs that already match the stock length can sit near the low end. Runs with several corners usually need the higher end. The percentage is an ordering allowance you choose. It is not a code factor.
How far apart should gutter hangers be?
A common residential range is about 24 to 36 inches, closer in snow or where the manufacturer requires it. This calculator defaults to 3 ft and uses hangers = ceil(measured run ÷ spacing) + 1 on each run. A 120 ft run at 3 ft spacing is 41 hangers. Follow the hanger and gutter brand, not a single universal gap.
Does roof pitch affect gutter sizing?
Pitch changes how fast water reaches the eave and how you convert a flat footprint into sloped roof surface. For drainage planning, the catchment is the projected area that drains to the gutter, not the sloped surface area. A steeper roof can also throw water past a small gutter. Use pitch as a planning factor, then check capacity against rainfall and the product rating.
Can I calculate gutters from house length and width?
Yes, if you also know which edges are guttered. A gable uses two eave runs. A hip can use the four sides. A shed roof usually uses the low side. Length times width is floor area, not gutter length, and 2 × (length + width) is the perimeter only when every side actually has a gutter.
Can this calculator estimate gutter cost?
Yes, when you enter your own prices. Gutter price applies to the adjusted order length. Downspout price applies to downspout footage only if you enter a drop height. Hangers, end caps, corners, and elbows use a price each. If every price is blank, no cost is shown. The page does not invent a price list.
Is this calculator a code-compliant engineering design?
No. It is a planning estimate. Gutter and downspout sizing depends on roof catchment, rainfall intensity, gutter profile, slope, outlet arrangement, local code, and manufacturer specifications. SMACNA, the International Plumbing Code, and local rainfall data are references for that check. They are not applied automatically here.
Related Roofing & Exterior Calculators
Gutter length, fascia, soffit, and roofing materials are separate takeoffs. To calculate roofing materials, start from roof area. Metal panel counts belong on the metal roofing calculator.
- Roof Area CalculatorRoof surface area from footprint and pitch. Not the gutter length.
- Roof Pitch CalculatorRise and run into pitch, angle, and the slope factor.
- Fascia CalculatorFascia board length along the same eaves and rakes.
- Soffit CalculatorSoffit area from eave length and overhang depth.
- Roofing Material CalculatorRoofing material quantities. A different takeoff from gutter length.
- Metal Roofing CalculatorPanel counts for a metal roof, not gutter stock.
This calculator provides planning estimates. Final gutter and downspout sizing can depend on roof catchment, rainfall intensity, gutter profile, slope, outlet arrangement, manufacturer specifications and local code. Verify the final system before purchasing or installing materials.