These project drawings call for 140mm x 45mm (1 1/2"x 5 1/2") lumber to be used for the seat and tabletop boards.
If the true size of the lumber that you are going to use is approximately 150mm x 50mm ( 2 x 6"), which is usually lumber
before it has been dressed, planed and/or seasoned, then go here >> picnic table project
For building instructions, materials list and a bit more about lumber sizes, go here >> instructions.
Plans for picnic table using 140mm x 45mm (1 1/2"x 5 1/2") stock.