1. On a spreadsheet, break your entire piece into each and every piece of wood. 2. Type out the width, height and depth of each piece in inches. 3. Here's how to turn that into a Board footage. (Width x Height x Depth)/144=The accurate Board Footage of the finished piece.
Here's the thing - If you go buy the board footage you just worked out, the moment you make the first cut, you no longer have enough wood for the project. You need to account for waste.
Here's an other vital point - You arent buying wood already cut to shape and size because you'll need to skim it down as you flatten and shape it so you're going to order wood thats at least 1/2 an inch thicker and a little longer than you'll cut it back to.
So for each piece of wood on your spreadsheet, figure out which one of the 3 dimentions represents the thickness of the wood you'll be working with.
For example - A drawer side might be 5" high x 20" deep x 1/2" wide so the board thickness will end up being 1/2 inch thickness but you'll actually buy 4/4 i.e. 1" thick wood from the lumber yard). See my point!
For that piece, you'll do this - 5" x 20" x 1"(4/4) = 100" cubed which you need to turn into feet cubed (board footage) so seeing as there's 144cubic inches in a board foot. it's 100" cubed / 144 to get 0.69444444 board feet at least that you'll be buying.
What else havent you considered?
Well if all you need to do is thin the board to flatten and straighten it you're good to go but thats not going to happen is it. Nope, you need to use your table saw/router etc at some point so you need to buy wood that's longer than you need to.
Here's where precision goes out of the window. Just add about 20% to the Board footage you have already worked out and you'll be ready to order your wood.
Example - I'm making a drawer side 5" high, 20" deep and 1/2" wide. So:
Of the 5" x 20" x 1/2", the 1/2" is the thickness of the board right?
To mill down to 1/2" thick you're gonna start with a 4/4" board (i.e.1")
So change it to (5" x 20" x 1" = 100 cubic inches)/144 = 0.69444444 board feet
Add 20% to this for saw cuts = 0.83333333 board feet. So go buy 0.85 board feet for this one component and you'll find that all you'll have at the end of the build are scraps of wood.
Also make sure that you buy wood to lengths that you can work with. The correct board footage is useless if half way through, you realize that you have enough wood left but you cant make a pivital piece of the project because none of the wood left is long enough to work with...