I tried on the two of the Altura range this week.... the Night Vision and the Nevis. I am a size 14, but I could get in the size 12, however the sleeves then came up short on me; the 14 was roomy and the sleeves long enough. I have broad shoulders and long arms, so if you were differently proportioned you might be able to go down a size, depending on the fit you wanted. (I feel the cold so want to be able to put a fleece underneath it). I did think that the Nevis felt slightly smaller than the Night Vision, but that may be just down to the style of the jackets. Also the Night Vision might be slightly longer in the back than the Nevis.