Have you ever found an amazing deal on a new blazer, only to find that your size is not in stock? It is possible to alter the fit of a blazer that is too big in many different ways. If it is too big in the body, the side seams can be taken in, or if the sleeves are too long, they can be taken up. An experienced tailor can alter a too-large blazer to a great fit.
Turn you blazer inside out and try it on. Assess the overall fit and note which areas are too big for you.
If the sides are too big: Pin along the side seams of the blazer to make it smaller. Leave enough ease so that the blazer is still comfortable and so that any pleats still lay flat.
If the sleeves are too long: Try the blazer on right side out and mark the sleeves with dressmaker's chalk at the correct length.
If the sleeves are too big: With the blazer on inside out, pin the under seam of the sleeves closer to your arms to achieve a better fit. Pin only the sleeve itself, not the lining.
Turn on your sewing machine, prepare the bobbin, and thread the machine.
If the sides are too big: Using the seam ripper, rip out the seam where the lining meets the jacket near the side seams. Measure the amount you will be taking in on the side seams and mark where you placed the pins using dressmaker's chalk. Remove the pins and pull the side seams out through the opening in the lining. Take the seam and pin in the amount you measured to take in. Begin from one end and baste along the side seam. Repeat on the opposite side.
Try on the jacket and adjust the fit as needed by ripping out the basting stitches and resewing the side seams. Once you have the fit you want, stitch up both side seams, and hand sew the lining back in place.
If the sleeves are too long: Use a seam ripper to undo where the sleeve meets the lining at the wrist on both sleeves. With the jacket inside out, pull the jacket sleeve down so that the sleeve ends where you marked it with dressmaker's chalk. Iron down the seam so that it lies flat. Hand sew the lining back to the sleeve and repeat on the other sleeve.
If the sleeves are too big: Use a seam ripper to rip the seam where the sleeve meets the lining at the wrist of both sleeves, and pull the lining back to the shoulder seam so that the whole unlined sleeve is visible. Transfer the pins from the outside of the sleeve to the inside. Baste along the bottom seam of both sleeves where you pinned it, removing the pins as you progress.
Turn the jacket right-side out and try it on. If the fit is unsatisfactory, rip out the basted stitches and resew the under seam of the sleeve. Once the fit is correct, sew along the under seam of the sleeve. Pull the lining back along the sleeve, and hand sew it in place around the wrist of the jacket sleeve.
If altering your blazer yourself proves too difficult, take it to a tailor.