A gutter miter is the corner fitting that carries rainwater around an outside or inside angle of a roof so a run of gutter can turn a wall corner without a downspout at every bend. It is the joint where two gutter sections meet at a 90 degree corner, and the way it is made decides how many seams sit at that corner, how much it costs, and how likely it is to leak. Three build styles dominate residential work: the pre-formed box miter, the strip miter, and the field-formed hand miter. This guide names each type, compares them in one table, explains inside versus outside corners, gives numbered install steps, and sets out what a corner typically costs.
By The Roofing Brief Team. Last reviewed August 2026.
What is a gutter miter?
A gutter miter is the corner piece in a gutter system that redirects water around a 90 degree turn in the fascia line. It lets a single downspout drain gutter runs from two sides of the house instead of forcing a downspout on each leg. Without a miter, water reaching a corner would simply overshoot the end and spill onto the ground below.
The word borrows from carpentry, where a miter joint is two pieces cut at matching angles to form a corner. In gutters, each straight run is usually cut at 45 degrees so the two ends meet cleanly at the corner, or a manufactured box slips over square-cut ends. Every gutter corner is either an inside miter (the gutter wraps toward the house, common at a roof valley) or an outside miter (the gutter wraps away from the house, the standard corner on most rectangular homes).
Miters are one named part in a larger assembly. To see where the corner sits relative to hangers, end caps, and outlets, review this gutter parts diagram naming every component.
Box miter vs strip miter vs hand miter: the types compared
The three common gutter miter types differ mainly in seam count and appearance. A box miter is a pre-formed corner with roughly three seams. A strip miter is a bent metal strip that leaves about one seam. A hand miter is field-formed from the gutter stock itself and can produce a nearly invisible corner. Fewer seams generally means fewer places to leak later.
| Miter type | Seams per corner | Relative cost | Appearance | Install difficulty | Best for |
|---|---|---|---|---|---|
| Box miter | About 3 (center plus each side) | Highest, often 2 to 4 times a strip miter per fitting | Bulky, sits proud of the gutter face | Easiest, runs slide into sleeves | Fast retrofit and DIY corners |
| Strip miter | About 1 (one sealed joint) | Low, the cheapest manufactured option | Low profile, flush with the gutter | Moderate, requires 45 degree cuts | New installs wanting a clean line |
| Hand miter (field miter) | 1 or fewer visible | Labor is the main cost, little hardware | Cleanest, matches the run | Highest skill, formed on site | High-end seamless gutter work |
| Bay miter | About 1 | Similar to a strip miter | Low profile at a wide angle | Moderate, 22.5 degree cuts | Non-90 degree bay window corners |
Box miter
A box miter is a pre-manufactured corner that gutter runs slide into, sealed with caulk at each side. It is the easiest type to install because there is nothing to cut or fold: the square-cut end of each gutter run inserts into a sleeve, typically with a 2 to 4 inch overlap, and gets riveted and sealed. The tradeoff is appearance and seam count. A box miter usually has about three seams (one down the middle and one where each run enters), and it sticks out from the gutter face, so it reads as an add-on rather than part of the run.
Strip miter
A strip miter is a one-piece bent aluminum strip, often around .027 gauge, that covers a single corner joint with roughly one seam to seal. Both gutter runs are cut at 45 degrees so their ends meet, and the strip is riveted over the back and outside face, then sealed. Strip miters cost less than box miters and sit low and flush, which is why they are common on new-home installs where a clean line matters. They demand accurate 45 degree cuts, so a good gutter cut is part of the job. See the tool and technique notes in how to cut gutter metal cleanly by material.
Hand miter (field miter)
A hand miter is formed on site by cutting and folding the gutter stock itself into a corner, producing the cleanest corner with one or no visible seam. It is the premium option in seamless gutter work because the corner is made from the same coil as the run, so color and profile match exactly and there is minimal added hardware. The catch is skill: hand mitering takes practice and time, so labor is the main cost driver and results vary with the installer.
Bay miter
A bay miter turns a gutter around a non-90 degree corner, such as a bay window, where the walls meet at a wider angle. It works like a strip miter but the runs are cut at 22.5 degrees instead of 45 so they follow the shallower turn. Use a bay miter anywhere the fascia angle is not a square corner, and confirm the exact angle on site before cutting.
Inside miter vs outside miter: what is the difference?
An outside miter wraps the gutter around a corner that points away from the house, which is the standard corner on most rectangular roofs. An inside miter wraps the gutter around a corner that points toward the house, which happens where two roof planes form a valley or an L-shaped or U-shaped footprint tucks a corner inward. Both box and strip miters are sold in dedicated inside and outside versions, so the part has to match the corner.
Inside corners matter more for water volume. A roof valley usually dumps concentrated runoff straight into an inside corner, so that corner sees more water than a plain outside corner and is a common overflow and leak point. Some suppliers sell an extended inside corner with a larger catch basin to handle valley discharge in heavy rain. If an inside corner overflows, the fix is often about capacity and sealing rather than the miter style itself.
How much does a gutter miter cost?
Cost depends on miter type and whether you buy the fitting or pay for labor to form one. A manufactured strip miter is the cheapest fitting, a box miter often runs 2 to 4 times the price of a strip miter per corner, and a hand miter carries little hardware cost but the most labor. On a professional install the corner is usually folded into the linear-foot price rather than billed as a separate line item.
Because pricing varies by region, material, and installer, treat any single number as a starting point and get a written quote. Aluminum is the most common and most affordable gutter metal, while copper and steel corners cost more. For how corner and material choices roll into the overall job, compare seamless gutter cost per foot by material.
How to install a gutter miter
Installing a gutter miter means joining two gutter runs at a corner and sealing the joint so it does not leak. The exact steps depend on whether you use a pre-formed box miter or a field-cut strip miter. Both start with a dry fit and end with sealant and mechanical fasteners, because a rivet or screw plus a quality sealant outlasts caulk alone.
Box miter install steps
- Dry-fit the box miter at the corner and mark where each gutter run needs to end, allowing a 2 to 4 inch overlap into each sleeve.
- Cut each gutter run square at the mark with tin snips or a gutter cutter, then deburr the edges.
- Slide the square-cut ends into the miter sleeves and check that the miter sits level with both runs.
- Drill and set rivets or gutter screws through the overlap on the back and bottom faces to lock the joint.
- Run a continuous bead of gutter sealant inside every seam, tooling it into the corner so no gap is left.
- Rehang the runs on the fascia at the correct slope and test with a hose, watching the inside of each seam for drips.
Strip miter install steps
- Cut the end of each gutter run at 45 degrees so the two ends meet cleanly at a 90 degree corner (use 22.5 degrees for a bay miter).
- Hold the two runs together at the corner and confirm the miter angle is tight with no visible gap.
- Secure the strip miter to the back of the gutter first so the mating run still slides into place easily.
- Rivet the strip over the outside face and bottom of the corner, spacing fasteners so the metal cannot flex apart.
- Seal the single joint line with gutter sealant on the inside, pressing it fully into the seam.
- Hang, slope, and hose-test the corner, resealing any weep before the system goes into service.
Whatever miter you install, the seam is only as good as the sealant. Match the product to the metal using this ranked guide to the best gutter sealant by gutter type. If an existing corner already leaks, diagnosing and resealing it is a separate job covered in how to seal a leaking gutter miter corner.
Frequently asked questions
What is a gutter miter?
A gutter miter is the corner fitting in a gutter system that carries water around a 90 degree turn in the roofline. It joins two gutter runs at a corner so a single downspout can drain both legs, instead of needing a downspout at every corner. Miters come as inside or outside corners and as box, strip, hand, or bay styles depending on the seam and appearance you want.
What is the difference between a box miter and a strip miter?
A box miter is a pre-formed corner that gutter runs slide into, with about three seams, a bulkier look, and the easiest installation. A strip miter is a bent metal strip covering one corner joint with roughly one seam, a lower flush profile, and a lower price, but it requires accurate 45 degree cuts. Box miters install faster, while strip miters look cleaner and leak at fewer points.
What is the difference between an inside and an outside gutter miter?
An outside miter wraps the gutter around a corner that points away from the house, the standard corner on most homes. An inside miter wraps the gutter around a corner that points toward the house, common where a roof valley or an L-shaped wall tucks the corner inward. Inside corners often catch valley runoff, so they carry more water and need extra attention to sealing and capacity.
Are box miters or strip miters better?
Neither is universally better; it depends on priorities. Box miters win on speed and DIY simplicity because the runs just slide into the fitting, which suits retrofits. Strip miters win on appearance and leak resistance because they sit flush and seal at about one seam instead of three, which suits new installs. Hand-formed miters give the cleanest corner but need a skilled installer.
How much does a gutter miter cost?
A strip miter is the cheapest manufactured fitting, a box miter often costs 2 to 4 times more per corner, and a hand miter carries little hardware cost but the most labor. On a professional install the corner is usually built into the per-foot price rather than billed separately. Prices vary by material and region, so treat any figure as a starting point and request a written quote.
Do seamless gutters still need miters?
Yes. Seamless gutters are run in single lengths along each straight side, but the metal cannot bend around a house corner, so every corner still needs a miter joint. That is why even a seamless system has visible seams at the corners. Installers minimize them with strip or hand miters, which reduce a corner to about one sealed seam instead of the three on a box miter.