A gutter elbow is the angled fitting that redirects water where a downspout has to change direction, and the two you will actually buy are the A elbow and the B elbow. An A elbow turns water toward or away from the wall (front to back). A B elbow turns water left or right along the wall. Get that one distinction right and the rest of downspout routing, sizing, and installation follows from it. This page covers the elbow types, the standard sizes, the common angles, and how to slip-fit and screw them so the joints do not leak.
This is the elbow-specific reference. For the full downspout run from the gutter outlet down to the ground extension, see our step-by-step downspout gutter installation guide. For where downspouts go and how many you need, see downspout placement and sizing.
A elbow vs B elbow: what is the actual difference?
The difference between an A elbow and a B elbow is the direction the water turns relative to the wall. An A elbow (sometimes called a front elbow) turns the flow front to back, toward or away from the wall. A B elbow (side elbow) turns the flow left or right, running the downspout sideways along the wall. Both are the same slip-fit fitting in the same sizes and angles; only the turn axis changes.
The fastest way to tell them apart on the shelf: hold the elbow so the open ends face you and the outlet. An A elbow bends in the same plane as the narrow face of a rectangular downspout, so it kicks water out or back. A B elbow bends across the wide face, so it kicks water to the side.
| Elbow | Turns water | Typical use | Common placement |
|---|---|---|---|
| A elbow (front) | Toward or away from the wall (front to back) | Bringing the downspout back to the wall at the top, then out at the bottom; building offsets | Top and bottom of most standard downspouts |
| B elbow (side) | Left or right along the wall | Routing around a corner, a door, a walkway, or a paved area | At the outlet or base when the run has to shift sideways |
A standard, no-obstruction downspout uses two A elbows: one at the top angling the pipe back to sit flush against the wall, and one at the bottom angling it out away from the foundation. You only reach for a B elbow when the path has to move sideways, which is why most homeowners see far more A elbows than B elbows on a house.
How do you choose between an A and a B elbow?
Choose the elbow by the direction the downspout must move at that joint. If the pipe needs to come toward the house or push away from the foundation, use an A elbow. If it needs to travel left or right along the wall, past a corner or an obstacle, use a B elbow. When a run has to move both sideways and out, you combine them: a B elbow to shift sideways, then A elbows to offset in and out.
- Water needs to go straight out from the wall: A elbow.
- Downspout needs to hug back against the wall from the gutter outlet: A elbow.
- Run has to skirt a corner, doorway, or walkway: B elbow.
- Downspout must clear a soffit, bay, or eave overhang, then return flush: two A elbows as an offset.
Gutter elbow types beyond A and B
Past the A/B distinction, gutter elbows are categorized by shape and by the pipe they fit. Rectangular elbows fit standard rectangular downspouts and come in A and B styles. Round elbows fit round downspouts, common on half-round and copper systems, and turn in any direction because the pipe is symmetrical. A few specialty pieces round out the catalog.
- Rectangular A and B elbows: the default for K-style aluminum and steel gutters.
- Round elbows: for round downspouts on half-round gutter systems and copper; no A/B split because the round pipe turns any way.
- Offset (kick-out) elbows: a pre-bent single piece that does the job of two A elbows plus a spacer, used to jog the downspout out past an overhang.
- Downspout outlets and adapters: not elbows, but they connect the gutter to the first elbow; covered in the downspout install guide.
Gutter elbow sizes: 2×3, 3×4, and round
Gutter elbow sizes match downspout sizes, and the two you will meet are 2×3 inch and 3×4 inch rectangular, plus 3 and 4 inch round. The elbow must match the downspout it joins. A 2×3 elbow on a 3×4 downspout will not seal, and a mismatched joint either leaks at the seam or works loose over time.
| Size | Shape | Best for | Rough capacity note |
|---|---|---|---|
| 2×3 in | Rectangular | Smaller single-story homes, average rainfall | The most common residential size |
| 3×4 in | Rectangular | Larger roof areas, heavy rain, gutters that overflow | Moves roughly twice the water of a 2×3 |
| 3 in / 4 in | Round | Half-round and copper systems | Match to the round downspout diameter |
If your existing gutters overflow at the downspouts during hard rain, upsizing the downspout and its elbows from 2×3 to 3×4 is often the fix, because the larger cross-section clears water faster. Sizing the whole system, not just the elbow, is covered in our roof rain gutter system design guide.
Gutter elbow angles: why most are 75 degrees, not 90
Most stock gutter elbows bend about 70 to 75 degrees rather than a full 90, because a gentler turn lets water accelerate through the curve instead of slamming into a hard corner and backing up. A softer bend also traps less debris, so the joint clogs less often. Sharper and gentler angles exist for specific routing needs.
- 75 degrees: the standard elbow; used for top and bottom turns and for building offsets.
- 90 degrees: a tighter turn for tight clearances, at the cost of more turbulence and clog risk.
- 45, 60, 30 degrees: gentler transitions for gradual routing or shallow offsets around trim.
What is a downspout offset (kick-out) and how far does it reach?
A downspout offset, also called a kick-out, uses two A elbows and a short straight section to jog the pipe out past an obstruction and then back flush to the wall. The first A elbow pushes the downspout away from the wall, a short filler piece of downspout spans the gap, and the second A elbow brings it back in. Two 75 degree elbows give a smooth S-curve that drains well.
The horizontal reach of an offset is set by the length of the straight filler piece between the two elbows, plus the small offset built into each 75 degree elbow itself. To clear a 6 inch soffit overhang, a short filler of a few inches between the elbows is usually enough; to clear a wider bay or a gutter that sits well outboard of the wall, cut a longer straight section. Keep the straight run pitched downhill so water does not pond in the horizontal span.
- Fit the first A elbow to the pipe coming down, angled out away from the wall.
- Measure the horizontal gap you need to clear, then cut a straight downspout section slightly longer to span it on a downward slope.
- Slip-fit the second A elbow onto the filler, angled back toward the wall.
- Check that the lower elbow lands the pipe flush against the wall, then fasten each joint.
How to install a gutter elbow so the joints do not leak
Install a gutter elbow by slip-fitting it so every downstream piece slides over the outside of the upstream piece, then securing each joint with two short screws. The one rule that prevents leaks is downstream over upstream: the piece going downhill wraps outside the piece above it, so water runs inside the connection rather than dribbling out a seam. Getting this backward is the single most common cause of a leaking downspout joint.
- Match the sizes. The elbow and downspout must be the same size and shape, 2×3 to 2×3 or 3×4 to 3×4. Mismatched pieces will not seal.
- Orient downstream over upstream. Slide the lower (downhill) piece over the outside of the upper piece at every joint so water stays inside.
- Dry-fit the whole path first. Assemble the top elbow, any offset, and the bottom elbow before fastening, so you can adjust before committing screws.
- Screw each joint. Use two short screws on opposite sides of the joint. Keep screws to about 1/2 inch; longer screws poke into the water channel and snag debris.
- Seal only if needed. A correctly lapped, screwed joint usually does not need sealant. Add a bead of gutter sealant only on a joint that still weeps.
Two screws per joint on opposite faces are enough to hold the elbow without crushing the pipe. Over-screwing or driving long screws through both walls creates snag points that build clogs at exactly the turn where water is already changing direction. Once the elbows and downspout are set, direct the discharge away from the house with a downspout extension so runoff does not pool at the foundation.
Common gutter elbow mistakes
The recurring elbow mistakes are size mismatches, reversed laps, and over-long screws. Each one shows up as a leak or a clog at the turn, and each is avoidable at install time. Fixing them later means pulling the joint apart, so it is worth getting right on the first pass.
- Using a B elbow where an A elbow belongs (or vice versa): the downspout ends up pointing the wrong way and has to be redone.
- Upstream over downstream: reversing the lap so water leaks out the seam at every joint.
- Screws longer than about 1/2 inch: they protrude into the flow path and catch leaves and grit.
- Skipping the pitch on an offset: a flat horizontal filler ponds water and freezes in winter.
For a wider view of how elbows fit into the whole drainage path, from gutter to outlet to ground, start with what a gutter is and its parts.
Frequently asked questions
What is the difference between an A elbow and a B elbow?
An A elbow turns water toward or away from the wall, front to back, and a B elbow turns water left or right along the wall. They are the same fitting in the same sizes and angles; only the direction of the bend differs. Most standard downspouts use two A elbows, one at the top and one at the bottom, and reach for a B elbow only when the run has to move sideways.
What size gutter elbow do I need?
Match the elbow size to your downspout: 2×3 inch is standard on smaller residential homes, and 3×4 inch suits larger roofs or heavy rainfall. Round elbows come in 3 and 4 inch for round downspouts. A mismatched elbow will not seal, so measure the downspout before buying and keep the size and shape identical at every joint.
Why are most gutter elbows angled 75 degrees instead of 90?
A 75 degree bend lets water accelerate smoothly through the curve instead of hitting a hard corner and backing up, and it traps less debris than a sharp 90. Tighter 90 degree and gentler 45 degree elbows exist for tight clearances or gradual routing, but 75 degrees is the default for standard top, bottom, and offset turns.
How do you keep a gutter elbow joint from leaking?
Lap every joint downstream over upstream, so the lower piece slides over the outside of the piece above it and water stays inside the connection. Match the sizes, secure each joint with two short screws about 1/2 inch long on opposite sides, and add sealant only if a joint still weeps. Reversed laps are the top cause of leaking downspout joints.
What is a downspout offset and when do you need one?
A downspout offset, or kick-out, uses two A elbows and a short straight section to jog the pipe out past an overhang, soffit, or bay, then back flush to the wall. You need one whenever the gutter sits farther out than the wall below it. Keep the straight filler pitched downhill so water does not pond between the two elbows.
Can you use an A elbow and a B elbow together?
Yes. When a downspout has to move both sideways and in or out, you combine them: a B elbow shifts the run left or right along the wall, then A elbows offset it out and back. This is common around corners and obstacles where a single elbow cannot reach the drop point in one turn.
Reviewed by The Roofing Brief Team. Last reviewed July 2026.