I have heart of pine very red boards that are 4” by 12’ long. I need to cover 680sqf. How many boards will I need? They are already togue and grooved.

4X144 divide by 144 will give you the square footage of one board. 680 divided by four equals how many boards will cover the floor. You may need more depending on the shape of your room(s). You should be able to use all the boards if they are perfect. The part of the last board in a row that you cut off can be used for the start of the next row, so you will have minimum cutting waste. Don't use any cut-offs that are shorter than 8 inches if you can help it. This is your cutting waste.