A jacket should close comfortably and let you move without pulling across the back. To choose a size online, start with the maker’s measurement diagram. Some brands ask for body measurements; others list the finished jacket. Comparing one with the other is a common source of mistakes.
Take your chest or bust measurement
Wrap a flexible tape around the fullest part, keeping it level across your back. Let your arms rest normally and breathe naturally. The tape should touch the body without squeezing. Measure over a light layer unless the brand instructs otherwise.
Follow the brand’s sleeve diagram
Sleeve measurements can start at the shoulder seam or at the centre back of the neck. Check the illustration before measuring. Keep your arm in the position requested and ask someone to help. Two results taken from different starting points cannot be compared directly.
Compare a jacket you already own
Lay a well-fitting jacket flat and smooth it without stretching. Record chest width, sleeve length and back length using the same points as the product listing. Note what you usually wear underneath it. A close-fitting blazer over a shirt is not a useful fit reference for a winter coat over heavy knitwear.
Allow for the way you will use it
Think through the ordinary movements: reaching forward, sitting down, lifting a bag or putting your hands in the pockets. A coat may look fine when you stand still but feel restrictive during those movements. Layering room is part of fit; it is not always solved by choosing one size larger.
- Everyday jacket: try it over the layer you wear most often.
- Winter coat: check room at the upper arms and shoulders with knitwear underneath.
- Tailored jacket: examine shoulder position and how the front lies when closed.
Between sizes?
Compare the chart’s chest, waist and sleeve measurements together. If the body fits but the sleeves do not, a different cut or length option may work better. Do not rely on a universal S-to-M conversion: the label is not a guarantee of finished dimensions.
Before removing the tags
Try the jacket indoors, check it from the side and back, and sit down with it fastened if appropriate. Make sure the collar and sleeves remain comfortable. Read the retailer’s return conditions before wearing it out.
For outfit planning, see our autumn layering guide. To compare trousers at the same time, use the waist and inseam guide.