BMW 4 Series (2015) is 279 mm (10.98 inch) longer, 74 mm (2.91 inch) wider, 40 kg (88 lbs) lighter and has 40 liters (1.41 ft3) bigger cargo space than Mercedes B-Class (2020).
Mercedes B-Class (2020) is 179 mm (7.05 inch) higher than BMW 4 Series (2015).