A jacket should let you wear the jumper you actually intend to put underneath it, with the front and sleeves sitting comfortably through ordinary movement. Test the complete combination. A good fit over a T-shirt does not establish a good fit over a thicker layer, and going up a size is not an automatic solution.
Start with a jumper from your own wardrobe, rather than imagining a generic winter layer. Its sleeve shape, neckline and thickness all affect how the two garments sit together. The checks below help you identify where a combination works and where a different cut may be more useful.
Prepare the outfit you will really wear
Put on the base top, jumper and trousers or skirt you expect to wear together. Settle the jumper sleeves before adding the jacket. If they bunch at the upper arm or cuff, rearrange them once and see whether they stay in place as you move.
A repeated need to pull or tuck the layers is useful information. You may be testing two incompatible sleeve shapes, rather than a jacket that is simply too small. Try your usual slimmer jumper as a comparison, if you have one, and note which layer creates the difference.
Check the fastening without forcing it
Fasten the jacket as intended. Notice whether it closes comfortably and whether the jumper gathers behind the front. If a zip, button or other fastening is under pressure, do not force it for the sake of completing the test.
Try the jacket open as well, but make an honest decision about how you will use it. Wearing it open may be a styling preference; it should not conceal a closure problem if you need to fasten it on your journey. The relevant fit is the one your day requires.
Move through three ordinary positions
First, reach both arms forward as though placing something on a table. Next, bend your elbows and bring your hands towards your face. Finally, sit in an ordinary chair with your feet comfortably placed. Move naturally rather than turning the exercise into a stretch test.
At each point, notice restriction, pressure or a layer moving out of place. Look at the back of the jacket as well as the front. A mirror or another person's observation can help you spot bunching, but your comfort remains part of the assessment.
Return to standing. Does the outfit settle on its own, or must you pull the jacket and jumper back into position every time? Some adjustment may be acceptable to you. Repeated disturbance during the movements you make all day may suggest a less practical pairing.
Look closely at sleeves and necklines
Check where the jumper and jacket cuffs finish when your arms are relaxed and when you reach forward. Decide whether you like the jumper cuff showing. Make sure the layers are not crowded simply to achieve a photograph's proportions.
Then compare the necklines. A high jumper neckline and a prominent jacket collar may sit comfortably together, or they may compete for space. Try the collar and fastening in the positions you intend to use. Add your usual scarf only if it is genuinely part of the outfit you need to assess.
Separate size from shape
If the combination fails in one area, identify that area before selecting another size. More room at the chest does not necessarily solve a narrow sleeve, and a larger size may change the sleeve length or shoulder position too. Read every relevant dimension supplied for both sizes.
Our guide to body and garment measurements explains how to compare chart values correctly. If the needed sleeve or measuring detail is missing, ask about it; do not estimate room from the model's pose.
Record a useful result
Write down the specific combination you tested and the result: “Comfortable fastened over my everyday jumper; cuffs need one adjustment,” or “Sleeves bunch when I reach forward.” These are examples of the sort of note to make, not claims about any ALBA product.
If you are considering Sabine, check its own current size and fit information against that note. Compare your preferred outfit with our short-jacket styling ideas once the layering fit is resolved. Choose a size and cut for the way you will wear the jacket, rather than for the size label alone.