You don’t have to be in shape to find a suit that fits.
Picking out the right suit means picking one with proportions that will make you look more athletic. Look for a suit that broadens your shoulders, enlarges your chest, slims your torso, and makes you look taller.
Broadening the Shoulders
The shoulders of a jacket shouldn’t be so wide that the head appears too small or so narrow that it appears too large. The jacket shoulders should meet up with the natural shoulder line, though they can extend 0.5 inches either side without looking exaggerated.
Enlarging the Chest
Lapels can make the chest appear larger or smaller depending on their size. Wider lapels have greater visual weight and therefore force the eye to linger on the chest, thus enlarging it. Unless you have has an extremely narrow chest or you prefer for extremely wide and aggressive lapels, a medium lapel width (about 8.5 cm) is a safe bet. Undersized lapels (7 or less cm) have the effect of making the chest appear underdeveloped.
Slimming the Torso
The torso can be slimmed by ensuring that the jacket is properly fitted around the waist This can be accomplished by checking for tightness around the jacket’s waist area . The jacket is too tight if X-like folds are forming around the waist button hole, and too large if it protrudes by more than 1.5 inches. The lapels of the jacket create diagonal vectors that naturally slim the torso and so they also shouldn’t buckle.
Creating the Illusion of height
Jacket length
To create the illusion of height, the jacket should extend below the trouser’s waistband and cover your arse. This lengthens the leg line by creating visual continuity between the trousers and the jacket. A basic test for the ideal jacket length, when the assistance of a tailor or qualified assistant is unavailable, is to relax the arms by your side and extend the thumbs so that they are parallel to the floor; the jacket should fall somewhere between the extended thumbs and the first knuckle of the first finger.
Trousers legs
Trousers should fall perfectly straight from the waist when standing. There should be no bunching as this disrupts the appearance of verticality.
Lapel Gorge
The lapel gorge describes the V-shaped formation that is created when the the lapels of the jacket meet. Because of their vertical vectors they increase the illusion of height. The average guys should have a lapel gorge located no lower than his navel and no higher than an inch above it to optimise the illusion of height.
Lapel Notch
The lapel notch describes the space where the collar of the jacket meets the lapel. The higher up the lapel notch is, the longer the vertical vectors of the lapels are, and the taller the wearer appears. For the average guy the notch should appear within the vicinity of the upper chest.
Vents
Vents create the illusion of height as they draw the gaze upwards. However ventless jackets also create the illusion of height as they do not disrupt the visual continuity of the rear. Vents are therefore often stylistic preferences. Italians tend to prefer to go ventless, Americans single and the Brits double. You’ll find all three styles down under.
Sleeves
Most men wear their sleeves far too long due to a common misconception that jackets sleeves should fit like shirts. On the average guy, sleeves should meet the wrist bone to permit some shirt cuff (at least 1/2 an inch but no more than 3/4 of an inch) to protrude. This prevents the arm appearing too short or too long.
(photos via. T-F.com, The Armoury, Voxsartoria, Jared Acquaro, Rose & Born, The Guardian, Rose Callahan)