BIRCH NUMBER 3 SHOP BIRCH NUMBER 3 SHOP grade is an economy grade that is used in upholstered furniture and sofa manufacturing. BIRCH NUMBER 3 SHOP grade utilizes both clear two-face cuttings and structurally sound cuttings in the board to make up the over-all minimum yield. Widths: 4 inch admitting (by volume) 5 percent narrows (85.73 mm) minimum. Lengths: Length: 72 inch (182.88 cm) minimum.. Minimum Size Cuttings: 3 inch (76.20 mm) wide by 24 inch (60.96 cm) and longer. Overall Minimum Yield: 33-1/3 percent.