Decide what the dimensions represent
An actual dimension is a measured physical size. A nominal size is a trade designation that may differ from the finished board. In the lumber calculator, the Actual / Nominal control records this distinction without changing any numbers.
If physical volume matters, enter the actual dimensions. If you are checking a supplier’s bill, establish which dimensions and rounding rules the supplier uses. Do not assume one automatic sizing table applies to every product and market.
Understand one board foot
One board foot is 144 cubic inches: a notional piece one inch thick, twelve inches wide and twelve inches long. A 1 × 6 inch piece eight feet long is four board feet by the entered dimensions. Four such pieces total sixteen board feet.
Allow for complete pieces
A 10% allowance on four pieces creates a target of 4.4 pieces, so the order becomes five. Different lines round separately. Pooling all their volumes could hide the need for a specific length or section.
The calculation does not find the best cutting arrangement. Keep a cutting list and check available stock lengths, defects, machining losses and the supplier’s pricing basis before ordering. Structural selection belongs to the relevant project design, not the volume estimate.