The 4 Series Convertible, based on the 4 Series Coupe, will be available with a choice of two petrol and a diesel engine at launch, with prices starting at £36,675 on the road.
Manual versions of th 184hp 420d SE have CO2 emissions of 133g/km, while those fitted with the optional eight-speed automatic have CO2 emissions of 127g/km.
Petrol variants at launch are an all-turbo line-up including the 245hp 2.0-litre 428i and 306hp 3.0-litre 435i.
The dimensions of the new car differ significantly from the outgoing BMW 3 Series Convertible. The overall length of 4,638mm has been extended by 26mm; the wheelbase has grown by 50mm and, together with the wider front track.
Unlike its rivals the Audi A5 Cabriolet and Mercedes-Benz E-Class Convertible, the BMW 4 Series has a three-piece electrically folding hard-top roof.