How to Cut Baseboard Inside Corners With a Miter Saw (No Gaps)

A basic inside-corner miter is two 45-degree cuts meeting at 90 degrees — but most wall corners aren’t exactly 90 degrees, which is why a “textbook” 45/45 cut often leaves a visible gap at the top or bottom of the joint. Professional trim carpenters check the actual corner angle first, then either adjust the miter or switch to a coped joint, which tolerates an imperfect wall far better than a miter does. This guide covers both methods and the back-cutting trick that hides small gaps either way.

Check the Corner Before You Cut

Before setting your miter saw to 45 degrees, hold a speed square or an adjustable bevel gauge into the actual corner. Real walls settle, and drywall corners are routinely 88 to 92 degrees instead of a true 90 — close enough that it looks square to the eye, but far enough off that two 45-degree cuts won’t meet cleanly. If the corner reads anything other than 90, split the difference: for an 88-degree corner, cut each piece at 44 degrees instead of 45; for 92 degrees, cut at 46.

Cutting the Miter (Best for Square-ish Corners and Simple Profiles)

1. Set the miter angle: Set your miter saw to 45 degrees (or the adjusted angle from your corner check) with the miter turned to the left for one piece.
2. Cut the first piece: Position the baseboard against the fence exactly as it will sit against the wall, and cut so the back edge of the board ends up slightly longer than the front edge — a “back-cut.” This tiny undercut means only the visible front edge has to fit tightly, which hides small gaps that would otherwise show at the face of the joint.
3. Flip the miter direction: Turn the saw to 45 degrees in the opposite direction for the second piece.
4. Cut the second piece: Cut with the same back-cut technique, then dry-fit both pieces together before nailing anything.
5. Test and adjust: If a gap shows at the face of the joint, shave one or two degrees off the cut angle on the offending piece rather than starting over on both.

Coping the Joint (What Trim Carpenters Actually Use)

Most professional trim installers don’t miter inside corners at all — they cope them. A coped joint butts one piece of baseboard square into the corner, then cuts the profile of the second piece to fit over the face of the first like a puzzle piece. Because the fit depends on the profile matching, not on two angled cuts lining up, a coped joint stays tight even if the wall corner is a few degrees off, and it stays tight longer as the house’s framing moves seasonally — a mitered inside corner is far more likely to open a visible gap after a year or two of wood movement.

1. Cut the first piece square: Butt it directly into the corner with a straight 90-degree cut.
2. Miter the second piece at 45 degrees: This exposes the profile of the molding as a cutting line.
3. Cope along the profile: Using a coping saw held at a back-angle (undercutting slightly, the same principle as the back-cut above), follow the exposed profile line so the front edge is the exact silhouette of the molding.
4. Test-fit and refine: Fit the coped piece against the square-cut piece and pare away high spots with the coping saw or a utility knife until it seats tightly.

Coping takes more practice than a miter cut, but it’s the standard for a reason: see our full coping saw for trim guide for the full technique, and our fret saw vs. coping saw comparison if you’re deciding which saw to buy for it.

Which Method Should You Use?

Situation	Best method	Why
Corner reads close to 90 degrees, simple flat profile	Miter (with back-cut)	Faster, and a near-square corner won’t show a gap
Corner is visibly off-square, or profile is detailed	Cope	Tolerates an imperfect angle and stays tight through wood movement
Baseboard will be painted, not stained	Either, back-cut miters are more forgivable	Caulk can hide a small miter gap on painted trim; it shows on stained trim

If you haven’t cut the straight runs yet, our guide on cutting baseboard with a miter saw covers the basic crosscuts before you get to corners, and cutting angles with a miter saw covers how the miter and bevel controls work together on compound cuts.

Frequently Asked Questions

Why does my inside corner miter leave a gap?

Almost always because the wall corner isn’t exactly 90 degrees. Drywall corners commonly run 88 to 92 degrees, so two cuts at exactly 45 degrees each won’t close cleanly. Check the actual angle with a speed square and split the difference across both cuts, or cope the joint instead.

Should I miter or cope inside baseboard corners?

Cope when the corner is visibly off-square or the profile is detailed — it’s the standard method professional trim carpenters use for inside corners specifically because it tolerates an imperfect angle. A miter is faster and fine for near-square corners with simple, flat profiles.

What is a back-cut and why does it matter?

A back-cut is a slight undercut that makes the back edge of the baseboard a hair longer than the front edge. It means only the visible front edge of the joint has to fit tightly, which hides small gaps that would otherwise be visible at the face of a mitered or coped corner.

What angle do I cut baseboard for an inside corner that isn’t 90 degrees?

Split the actual corner angle in half across both pieces. For an 88-degree corner, cut each piece at 44 degrees instead of 45; for a 92-degree corner, cut at 46 degrees each. Always test-fit on scrap first.

Can I use a coping saw instead of a miter saw for inside corners?

Yes — you still need the miter saw to cut the first piece square and to cut the 45-degree guide angle on the second piece before coping it, but the coping saw does the actual profile cut that makes the joint fit.

Bottom Line

A plain 45/45 miter only works when the wall corner is genuinely square, which is less common than most guides assume. Check the actual angle first, use a back-cut to hide small gaps, and switch to coping for anything off-square or detailed — it’s more work up front but holds its fit far longer than a miter does.