Women's suits are extremely professional and flatter most figures if they fit well. Business suits that are ill-fitting look borrowed and sloppy. There are a few general guidelines to keep in mind, but remember to buy in a shape that flatters your body type and makes you comfortable.
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The jacket should slide on comfortably and not be too tight or too loose anywhere. The collar should end in the middle of your neck and not seem to stand up too high and the jacket fabric should not wrinkle or roll under the collar in the back. The shoulders should sit straight without pulling or sticking out from your shoulders. If the suit has shoulder pads, they should look natural and not stick up too high. With your arms hanging straight down at your sides, the sleeves should cover your whole wrist bone but not hang all the way down to your hands. Raise your arms and lower them again. If the jacket fits you well, it should fall more or less back into place when your arms are lowered. If you need to adjust it too much, it does not fit you well. Try sitting down with the jacket buttoned. It should be comfortable and not pull at the buttons or bunch up anywhere.
The trousers should allow you to move comfortably and still flatter your shape. You should be able to get your index finger between the trousers and your waist. If you can't, the trousers are too tight. The fabric shouldn't pull at all around the button or hook closure or pucker at the seams. The pants should lie flat against the front of your legs when standing. If the fabric puckers, they are probably too tight. The crotch seam should fit your body both when you stand up and when you sit down. A seam that is too low will look sloppy, while a seam that is too high will be uncomfortable and may be inappropriate. Try sitting down in the trousers. The outer seams shouldn't pull, and it should be comfortable. This is especially important if your job requires you to sit for long periods of time. The hem of the pants will come up a bit when you sit, but it shouldn't be much above your ankle. Wear the shoes you'll be wearing most with the suit. The hem of the trousers should come just to your instep in front and cover half your heel in back. If you can't find the correct length at the store, buy trousers that are too long and have them altered.