15.4 inch bag :  Outer dimension  390 x 275 x 35 mm ,   Inner dimension : 370 x 260 x 30 mm .
Pls kindly understand the bag maybe a little loosen or tighten for your laptop.
Own such as 13.3" laptop, it means laptop display screen is 13.3", all laptop screen frame is not same dimension.
All different model laptop 13.3", they all are different outer dimension, our 13.3" bag cann't perfect fit all 13.3" laptop.