How to Cut Outside Corner Baseboard Molding (Angle Chart)
Cut outside corner baseboard molding by mitering both pieces at matching angles that add up to the corner’s true angle — 45° each only if the corner is exactly 90°, which older homes rarely are. Cutting two 45° miters on an 88° corner leaves a visible gap at the tip. This guide covers measuring the real corner angle, setting the saw correctly, and why coping (unlike inside corners) is never the fix for a bad outside miter.
Quick Answer
For a square 90° outside corner, set the miter saw to 45° on each piece. For any other corner, measure the actual angle with a protractor or digital angle finder, then set the saw to 90 − (corner angle ÷ 2). Outside corners are always mitered — never coped; coping is an inside-corner technique only.
Tools You Need
A clean outside miter depends more on accurate measurement than on the saw itself. Four tools cover nearly every outside-corner cut:
- Miter saw — a compound miter saw is the standard tool for baseboard; a miter box and hand saw work for small jobs.
- Digital angle finder or protractor — reads the real corner angle so you’re not guessing at 45° on a wall that isn’t square.
- Combination square — confirms whether a corner reads as square before you trust the protractor number.
- Coping saw — not for outside corners, but essential if the same room also has inside corners to fit (see the comparison below).
Measure the Real Corner Angle First
Never assume an outside corner is exactly 90°. Framing settles and drywall corners get built up with mud, so a corner that looks square is often 86° to 94° in practice. Press a digital angle finder or protractor into the corner and read the actual angle before you touch the saw.
The formula: once you know the corner’s actual angle, the miter saw setting for each piece is 90 − (corner angle ÷ 2). For a true 90° corner that works out to the familiar 45° on each side. For anything else, the two pieces need matching, non-45° miters to close the gap.
| Measured Corner Angle | Saw Setting (Each Piece) | Notes |
|---|---|---|
| 86° | 47° | Common in slightly bowed or settled walls |
| 88° | 46° | Close to square — easy to miss without a protractor |
| 90° | 45° | True square corner — the standard cut |
| 92° | 44° | Slightly open corner |
| 96° | 42° | Noticeably open — test-cut scrap first |
Cut both pieces at the same setting, then dry-fit them against the wall before nailing anything. If the tip gaps open on the face side, the actual angle ran slightly narrower than measured — add half a degree and re-cut on scrap first.
How to Cut the Outside Corner
- Measure the wall length: measure from the corner to the nearest obstruction or the next joint, and mark the molding on its face side, where the cut will be visible.
- Set the saw to the calculated angle: use the table above — 45° for a square corner, otherwise the angle from your measurement.
- Cut the first piece: hold the molding flat against the saw’s fence exactly as it sits on the wall, and cut so the long point of the miter lands on the face side.
- Cut the second piece as a mirror image: flip the miter direction so the two long points meet at the corner, not past it.
- Dry-fit before nailing: hold both pieces against the corner. A hairline gap at the very tip is normal and will close under a nail; a wedge-shaped gap means the angle needs adjusting.
Why You Don’t Cope an Outside Corner
Coping and mitering solve different problems, and mixing them up is the most common mistake in outside-corner work. A coped joint — where one piece is cut square and the other is scroll-cut to match its profile with a coping saw — is built for inside corners, because it hides seasonal wood movement without opening a visible gap. On an outside corner there’s no profile to trace against; the two square edges have nothing to cope to. Outside corners are mitered, full stop — if a mitered outside corner isn’t closing tight, the fix is re-measuring the angle, not switching to a coping saw.
| Inside Corners | Outside Corners | |
|---|---|---|
| Technique | Coped joint | Mitered joint |
| Tool | Coping saw (after a 45° miter guide cut) | Miter saw only |
| Handles wall movement? | Yes — gap stays hidden | No — gap shows immediately |
| Handles an out-of-square corner? | Yes — scribe to fit | Only if you measure the real angle first |
Best Angle-Finder Pick
GemRed Digital Angle Finder Protractor
Reads a wall corner’s actual angle to within about 0.3° so you can set the miter saw correctly instead of assuming 90°.
- Best for: out-of-square corners in older homes
- Why we picked it: locks the reading so you can transfer it straight to the saw’s angle scale
- Main drawback: runs on a coin-cell battery; no reverse-angle display
Compare more outside-corner cutting tools
 Option 1 Metabo HPT 10″ Compact Miter Saw
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 Option 2 KAKURI Coping Saw + 5 Blades
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 Option 3 GRENPRO Combination Square Set
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Attaching and Finishing the Molding
Once both miters dry-fit tight, install the piece before moving to the next corner — test-fitting an entire room’s molding before nailing anything increases the chance a piece shifts.
- Run a bead of construction adhesive along the back of the molding, concentrated near the mitered end.
- Press the piece to the wall and hold the miter tight to its mate at the corner.
- Nail with a finish nailer every 16 inches along the flat run, plus one nail through each side of the miter itself to lock the joint closed.
- Set the nails slightly below the surface, fill with wood filler, and let it dry fully before sanding.
- Caulk the top edge against the wall and any hairline gap at the miter tip, then sand smooth and paint or finish to match the room.
Frequently Asked Questions
What angle do you cut trim for outside corners?
45° on each piece, but only if the corner is truly 90°. Measure first with a protractor or angle finder — on a corner that reads 86° or 94°, cutting a flat 45° on both pieces leaves a visible gap at the tip.
Do you cope outside corners?
No. Coping is exclusively an inside-corner technique, where one piece is scroll-cut with a coping saw to match the profile of the piece it butts against. Outside corners have no profile to cope to — they’re always mitered.
How do you cut a baseboard corner that isn’t 90 degrees?
Measure the actual angle with a protractor or digital angle finder, then set the miter saw to 90 minus half that angle on each piece. An 86° corner needs two 47° cuts; a 96° corner needs two 42° cuts. Test on scrap before cutting the final piece.
Why won’t my outside corner miter fit tight?
Almost always because the corner isn’t actually 90° and both pieces were cut at a flat 45°. Re-measure the corner angle directly rather than assuming it’s square, and check that the molding sat flush against the saw fence during the cut — any lift changes the resulting angle.
How do you cut 90 degree trim?
Confirm the corner is square with a combination square, then set the miter saw to 45° and cut each piece as a mirror image so the long points of the miters meet at the corner.
What glue or fasteners hold an outside corner miter together?
Construction adhesive on the back of both pieces plus finish nails through each side of the miter joint itself — nailing through the corner from both directions is what keeps the tip from opening over time.
The difference between a tight outside-corner miter and a gapped one almost always comes down to one step: measuring the real corner angle instead of assuming 90°. Reach for the protractor before the saw, use the 90 − (angle ÷ 2) formula for anything off-square, and remember that outside corners are mitered — never coped. Get that right and the rest of the installation is routine.
