Whether a blazer or suit jacket fits or not, according to convention, is most obvious in the length of the sleeves and at the waist. As a ‘rule of thumb’, the shirt cuff should end about 3 centimetres from the thumb knuckle (mcp joint), while the jacket sleeve should end about 1.5-2 centimetres above the shirt cuff, on the wrist bone.
The jacket should fit slim but not tight, with little excess fabric at the sides. If the upper button can be closed without either a large gap between the body and the jacket or a horizontal crease over the chest, the fit is right. (A common test is to put a finger between the chest and the upper button; one finger is a good fit but if there is room for two, the jacket is too big.) Two- and three-button jackets are cut with a slight flare from the waist, which means that the bottom should always remain un-fastened to ensure a proper fit and drape.
The shoulder seam should run exactly on top of the shoulder bone and meet the sleeve where the arm meets the shoulder – not above it or outside it, both resulting in a ‘ripple effect’ with creases and wrinkles around the shoulder.
A suit trouser should be either ‘classic’ length or distinctively cropped, not somewhere in between. The classic fit means that the trouser’s hem rests slightly on the shoe, falling a touch longer in the back, with a subtle break in the fabric above the foot.