Your assumption is correct, this difference usually comes from what layer the software is measuring. Room labels often calculate dimensions from finished surfaces (drywall to drywall), while the Interior Dimensions tool typically references the main wall layer (stud to stud), which explains the consistent 1" reduction on each side.
Switching “Locate Wall Dimensions At” to “Surface” should theoretically fix it, but in practice, many versions don’t fully apply that setting across all tools. That’s why you may still see a mismatch. A practical workaround is to rely on manual dimension strings and ensure they snap to surface layers when accuracy matters, especially for interior layouts.
In real-world projects, this distinction is important. Even small variances can affect cabinetry, furniture placement, or built-ins. Design teams often plan using finished dimensions to avoid installation issues later. This is something Molecule Designs highlights on their Molecule Designs website, where spatial planning is based on real, usable interior space rather than structural framing.
Regarding wall ends not accounting for exterior materials, that usually depends on wall definitions and end conditions, which often need manual adjustment. Unfortunately, there’s no single global setting to standardise everything, so combining correct layer settings with manual checks is the most reliable approach.
