Gutter IQ
The short answer
Measure the eaves, not the perimeter. Gutter hangs on the horizontal roof edges where water sheds. It does not hang on rake edges, the sloped edges of a gable. Add up eave runs only, then count miters, downspout drops and drop heights.
Everything else on a gutter job, coil, hangers, end caps, outlets, sealant, is derived from that one eave figure.
On this page
Eaves, not perimeter
This is the whole discipline of gutter measuring in one sentence, and it is worth being precise about why.
A roof has two kinds of edge. An eave is horizontal: it is the low edge of a slope, and water runs off it. A rake is sloped: it is the edge that climbs the gable end from eave to ridge, and water runs along it rather than off it. Gutter goes on eaves.
On a straightforward hip roof, every edge is an eave, so the roofline perimeter and the gutter run are close to the same number. On a gable, they are not. A simple rectangular gable house has two eave runs and two rake edges, and the rakes can easily be a third of the perimeter. Quote that house off the perimeter and you have overstated the gutter by a third before you have made a single other error.
Break the total into runs
The total eave footage tells you how much gutter to make. The breakdown into separate runs tells you how to hang it. A run is a continuous length of gutter between two ends, and it matters for three reasons: every run needs at least one downspout, long runs need more than one, and the run length sets where the slope has to fall.
So record the runs, not just the sum. Two hundred feet in one continuous wraparound run is a different job from two hundred feet in six separate runs, even though the coil order is identical.
Counting miters
Every change of direction inside a run is a miter, and miters drive both material and labor. Two kinds:
- Outside miters wrap an external corner, like a bump out or a bay.
- Inside miters turn an internal corner, like the inside of an L shaped or U shaped house.
Count them off the roofline rather than the floor plan. Dormers, bay windows and cantilevers add corners at the eave that a footprint drawing does not show. If you form your own miters from coil rather than buying them, they also consume extra coil, which is one of the things a waste percentage is standing in for.
Downspout drops and heights
The drop count comes from drainage, not from the gutter footage. Sizing them properly is its own subject and we have written it up separately in how many downspouts do I need. For the takeoff itself you need three things per drop: where it lands, how tall it is from gutter to grade, and whether it has to jog around an overhang.
Drop height is the part most often skipped, and it is also the part aerial measurement cannot give you. A two dimensional image has no vertical dimension, so downspout height is a site observation or a story count. Two stories is roughly 20 to 24 ft of stock per drop against 10 to 12 ft for a single story, so guessing it wrong on a six drop house moves the material order by 60 ft or more.
Three ways to get the number
| Method | Good for | Where it falls down |
|---|---|---|
| Satellite or aerial trace | Quoting from the desk before deciding whether the job is worth a drive. Trace the eave line and read the length off. | Imagery older than the last addition or reroof. Heavy tree cover over the eave. No vertical dimension, so no drop heights. |
| Phone AR or LiDAR | On site, long runs, and getting drop heights without a ladder. Faster than a tape for anything over about 15 ft. | Bright direct sun, glass and water degrade the reading, and it needs you at the property. |
| Wheel, tape or laser | The check measurement, and any run where the other two disagree with what you can see. | Slow, needs the site, and eave edges over landscaping or a deck are awkward to reach. |
The practical pattern most contractors settle into is trace from above to price the job, then confirm the drops and anything ambiguous on site when they go to sell it.
Where roof pitch does and does not matter
Worth separating, because it causes real confusion.
Pitch does not change gutter length. The eave is horizontal. A 12 in 12 roof and a 4 in 12 roof over the same footprint have the same eave run, so the coil order is the same.
Pitch does change how much water arrives, and how fast. Steeper roofs deliver runoff with more momentum, which is why sizing guidance multiplies the drainage area by a pitch factor before choosing a gutter and downspout size. The commonly published factors are 1.0 for flat through 3 in 12, 1.05 for 4 to 5 in 12, 1.1 for 6 to 8 in 12, 1.2 for 9 to 11 in 12, and 1.3 for 12 in 12 and steeper. Note that the largest of those is 1.3, so pitch on its own rarely forces a size change. It is a multiplier on top of area and rainfall intensity, and those two do the heavy lifting.
Turning the measurement into material
Once the eave figure is honest, everything else falls out of it:
- Coil: eave footage plus waste, one foot of coil per foot of gutter. Run it through the coil calculator to get pounds and rolls.
- Hangers: eave footage divided by your spacing. Commonly quoted at 24 to 36 in on center, tightened to 16 to 18 in where snow and ice sit for long periods.
- End caps: two per run, minus any that die into a wall.
- Outlets: one per drop.
- Downspout stock: drops times drop height, ordered as its own coil in its own width and gauge.
- Miters: the count you took, inside and outside kept separate.
The five mistakes that inflate a takeoff
- Using perimeter instead of eaves. The big one. Costs you the bid on gable houses because you are quoting gutter that will never be hung.
- Measuring at the wall line. The gutter hangs off the fascia at the eave edge, which on a deep overhang traces a noticeably larger rectangle than the footprint.
- Baking waste into the measurement. Keep the measured number honest and apply waste at the order. Otherwise nobody remembers what is already padded, and the padding compounds.
- Guessing drop height. No aerial measurement can see it. On a two story house it is the difference between a right order and a second trip to the supply house.
- Counting corners off the floor plan. Dormers and bays add eave corners that the footprint does not show.
Common questions
How do you measure for gutters?
Add up the eave runs only, the horizontal edges where the roof sheds water. Do not include rake edges, the sloped edges of a gable, because no gutter hangs there. Then count inside and outside miters, count downspout drops and measure their height from gutter to grade, and note which runs are separate so you can plan the drops. Eave footage is the number every other quantity keys off.
What is the difference between roofline perimeter and gutter footage?
Perimeter is every edge of the roof added together, eaves plus rakes. Gutter footage is the eaves only. On a simple hip roof they are nearly the same number, because a hip has eaves on all four sides. On a gable they are very different, because the two sloped rake edges carry no gutter. Quoting a gable house off the perimeter overstates the job, sometimes by a third.
Can you measure gutters from satellite imagery?
Yes, for most residential properties, and the eave line is easier to trace than a full roof takeoff because you are following one continuous edge rather than classifying facets. The limits are the same ones that affect any aerial measurement: imagery older than the last addition or reroof, heavy tree cover over the eave line, and new construction. Those fail visibly rather than silently, so you can usually tell when to go look.
Do you measure gutters before or after the roof overhang?
Along the outer edge of the fascia, which is where the gutter actually hangs. Measuring at the wall line rather than the eave edge shorts the run on any house with a deep overhang, because the eave edge traces a larger rectangle than the footprint does.
How do you count miters?
Every change of direction in a continuous run is a miter. An outside corner where two eaves meet around a bump out is an outside miter, and the inside corner of an L shaped or U shaped house is an inside miter. Count them from the roofline rather than the floor plan, because dormers and bays add corners at the eave that the footprint does not show.
How much extra should I add to a gutter measurement?
Nothing, to the measurement itself. Keep the measured run honest and apply waste separately when you order material, so you always know which number is measured and which is padded. Mixing a fudge factor into the measurement is how a number that was 8 percent high on the first job becomes 20 percent high three jobs later, because nobody remembers what is already baked in.