What Omni's lumber weight tool does
The fetched Omni lumber weight page combines basic board volume with a species density chart. Once you know the board dimensions and the wood density, the weight follows directly from volume times density.
Weight relationship
Volume = Thickness x Width x Length
Weight = Volume x Density
This version uses common densities from the same kind of species chart Omni provides, while also allowing a custom density for exact project stock.
Practical use
Lumber weight matters for transport limits, hoisting plans, storage loading, and checking whether a built-up beam or timber package can be handled safely on site.