Inside trim corners — cope the joint instead of mitering it

Join inside corners with a coped joint, not a miter: the first piece butts into the corner and the second is back-cut to its profile. A mitered inside corner opens up because no drywall corner is truly square.

Source: Finish-carpentry practice (AWI 0620); per the calculator’s installation notes

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What this diagram shows

A top-down comparison of two baseboards meeting at an inside corner. On the wrong side the two pieces are each cut at 45 degrees and mitered together; because the joint depends on a true 90-degree corner, it springs open into a visible gap as the wood shrinks or because drywall mud rounds the corner. On the right side the joint is coped: the first piece runs square into the corner and butts the wall, and the second piece has its end back-cut to the moulding’s own face profile so it laps tightly over the first and the seam stays closed.

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    <img src="https://remodelcalculators.com/api/figure-embed/trim-cope-vs-miter" alt="A top-down comparison of two baseboards meeting at an inside corner. On the wrong side the two pieces are each cut at 45 degrees and mitered together; because the joint depends on a true 90-degree corner, it springs open into a visible gap as the wood shrinks or because drywall mud rounds the corner. On the right side the joint is coped: the first piece runs square into the corner and butts the wall, and the second piece has its end back-cut to the moulding’s own face profile so it laps tightly over the first and the seam stays closed." width="800" height="450" style="width:100%;height:auto;border:0" loading="lazy">
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    Diagram: <a href="https://remodelcalculators.com/construction-diagrams/trim-cope-vs-miter" target="_blank" rel="noopener">Inside trim corners — cope the joint instead of mitering it</a> — courtesy of <a href="https://remodelcalculators.com" target="_blank" rel="noopener">RemodelCalculators.com</a>
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