A dimension is a line, not a finished-fit promise
Start with nominal panel geometry, then test your stock.
The base is measured between score lines
The example has a 100×70 mm base and 25 mm walls. Those are nominal panel dimensions in the flat pattern. They are not a measured inside clearance after thick card, glue and folds have been added.
Its flat envelope is (100+2×25) by (70+2×25), or 150×120 mm. Tabs sit in the four corner spaces inside that envelope. The geometric base volume is 100×70×25÷1000 = 175 mL; that is arithmetic, not usable capacity, strength or suitability for liquids.
Why tab reach is bounded
A tab is attached to each end of the front and back wall. Its reach must stay at least 2 mm below wall height and at least 1 mm below half the base width. This keeps the flat tabs within the wall envelope and avoids opposing tabs reaching across the whole side panel. The angled outer corners remove a small wedge.
Prototype before committing
Cut a trial from scrap paper, fold it and compare with the object you want to hold. Then try your chosen stock. Fold radius, score width, thickness, adhesive and assembly all affect finished fit. FoldBench does not add board-thickness compensation, lid clearance, kerf, bleed or manufacturing tolerances.