While the design of the new B-Class continues to offer space in abundance, the line's new dynamic character is directly apparent in its exterior dimensions. The most striking aspect is the reduced height: at 1557 millimetres, the new model crouches almost five centimetres lower on the road than its predecessor. The seat height in relation to the road has also been reduced (minus 86 mm). At the same time, this seat height also makes rolling movements substantially less noticeable.

In response to requests from many customers, the sitting position is more upright, however. At the same time, the headroom has been further improved. With maximum headroom of 1047 mm at the front (without sliding roof), the B-Class is among the most spacious cars in its segment in this discipline, too. The ergonomically expedient more upright sitting position in combination with a lowering of the vehicle's floor at the rear leads to a segment-leading degree of legroom (976 mm).

The B-Class offers plenty of space for luggage, too. The luggage compartment has a capacity of 488 litres on the basic model. Even more important than this abstract volumetric measurement is the actual usable volume. The B-Class comes up trumps here with a luggage compartment width between the wheel arches of 1050 millimetres (40 mm more than its predecessor). Six crates of mineral water, each containing 12 0.7-litre bottles, or three medium-sized packing cases (measuring 440 x 345 x 470 mm) can be transported without encroaching on the space available in the second row of seats. As a particularly convenient feature, the loading sill has been lowered by five millimetres in comparison to the predecessor and is now at a height of 616 millimetres.

The rear seat backrest comes as standard in a folding variant with a 60:40 split. As an option, the B-Class is alternatively available with the so-called EASY-VARIO-PLUS system. This enables flexible reorganisation of the interior in next to no time. Features of the EASY-VARIO-PLUS system include separate fore/aft adjustment of the rear seats by up to 140 millimetres. The luggage capacity then increases from 488 to 666 litres.

The inclination of the rear seat backrest is also adjustable. In so-called cargo position, a washing machine can be transported with the tailgate closed without folding the backrest down, for example. Equally, nine crates of mineral water or six medium-sized packing cases fit under the tailgate in this position. With the EASY-VARIO-PLUS system, the backrest of the front passenger seat can additionally be folded down onto the seat cushion to enable the transportation of long objects.

The height-adjustable luggage compartment floor also offers added variability according to individual needs. It can be moved into two different positions with one hand and locked firmly into place. In the upper position the luggage compartment floor forms a continuous surface with the load sill, facilitating loading and unloading. The rear seat backrests can be folded forward to produce a level load surface. An additional 72 litres of stowage space is then available under the loading floor. On the basic version the floor is limited to the lower position, but is removable.

The deployment of the electric parking space and the resultant omission of the handbrake lever gives rise to key advantages regarding the design of the tunnel trim and the area of the centre armrest. A stowage compartment has been integrated in the resultant space under the hinged armrest, which is optionally available as a sliding version. The interfaces to the mobile communication devices are located here: AUX (option: UCI) and USB connection and the entire comfort telephony.

In conjunction with the DCT transmission, whereby the shift lever is relocated from the tunnel trim to the steering wheel as the DIRECT SELECT lever, additional stowage space becomes available, Other stowage facilities include the door pockets, which now securely accommodate 1.5-litre bottles on the driver's and front passenger's side. A special compartment for the reflective safety jacket which is required in many countries is also to be found here. There is an umbrella holder next to the driver's and front passenger's seat, and stowage compartments are incorporated on the left and right of the luggage compartment. Optional extras include fold-out stowage compartments under the driver's and front passenger's seat, folding tables on the front seat backrests and an insert for a double cup holder for the stowage compartment in the tunnel trim between the front seats.