Sewing tutorial

Make Your T-shirt Bigger

Common t-shirt sizes include extra small, small, medium, large, extra large, and extra extra large. If your size is not available, you may buy a larger t-shirt and increase the seam allowance and/or hem to make it smaller. If your t-shirt is too small, making it fit better is more involved. This is a make your t-shirt bigger tutorial.


It’s been a few years since I bought new summer clothes. Some of the old ones are worn out and others fit poorly. I bought some new t-shirts and I want to make some of the old ones bigger so that I can wear them.

This tutorial shows you how to make your short sleeved and long sleeved t-shirts bigger by adding new panels.


  • fabric marking pens/chalks
  • scissors or rotary cutter
  • ruler
  • sewing machine
  • ball point sewing machine needle(s)

Seam allowance: 1/4” (0.6 cm)

Widen It

You can widen your t-shirt by adding vertical panels along the side seams.

Short Sleeves
Step 1 Gather Materials

For this project you will need a t-shirt that fits well, t-shirt that is too small and some knitted fabric of a similar weight to the too-small t-shirt. If you have many shirts that are too small, your may use some of them as material for making other t-shirts bigger.

I choose a black, short sleeved t-shirt that was a good length for me but small around. Here it is compared to another t-shirt that fits well width-wise and is a bit too long.

Black t-shirt on top of a larger, pale t-whirt
Black t-shirt is too narrow
Step 2 Measure

Try on your t-shirt to determine where it’s too small. Take it off and place it on top of a t-shirt that fits better. Smooth both t-shirts out on a firm surface and align the shoulder seams. Try to centre the small shirt on the larger one. Measure the difference in width between the two t-shirts.

Close up of ruler showing pale shirt is 2" wider than black shirt
Pale shirt is 2″ wider on each side

The maximum difference in width between my two t-shirts is 2”.

There are two layers of shirt (the front and back) so multiply this width by two. The panel also needs a seam allowance along each edge. My shirt was sewn with a 1/4” seam allowance so I used it for the panel seam allowance.

The width of each side panel is 2 times (difference in width + seam allowance). For my black t-shirt each panel is 4.5” wide.

I used a tailors measuring tape to measure my black t-shirt along the side and underarm seam from the unfolded bottom hem to the unfolded sleeve hem. This length is the height of each side panel. For my black t-shirt, the height of each panel is 21.5”.

You may wish to taper your panels if you don’t need the same width along the entire height.

To widen my black t-shirt, I need to add two panels (one for the left side and one for the right side) that are 4.5” wide and 21.5” tall.

Step 3 Cut

Cut your t-shirt along the side seams and underarm seam. Rip the hems along each side of the cut seams so that you can unfold it.

Seams cut open on black t-shirt
Cut along the seams

Double-check the width for each panel. Double-check the panel length along the cut seam, paying attention to any slight curves in your t-shirt.

Cut out your two panels. The direction of longest stretch needs to go around your body.

Vertical strip of black fabric 4.5" wide
Side panel cut from donor t-shirt
Step 4 Sew Panels

Pin or clip your vertical side panels along the cut seams of your t-shirt, right-sides together. Line up the edges so that you can hem the bottom and sleeves.

T-shirt with strips of fabric clipped to ti
Clip side panels along cut edges

If you have a serger you can sew your new panels into your t-shirt and finish the edges in one step.

Use your sewing machine if you don’t have a serger. Follow your machines instructions for using the overlock stitch if you have one. If your sewing machine does not have an overlock stitch, sew the seams with a straight stitch then use either a zigzag stitch or elastic stitch to secure everything in place. Zigzag and elastic stitches will stretch with the fabric when you put your t-shirt on and take it off.

Step 5 Hem

Hem the bottom and sleeves of your now bigger t-shirt. Sew the hem with a zigzag stitch or elastic stitch.

Close up of hemming a t-shirt
Hem the new panels

If you cut your vertical panels from another t-shirt, use it’s pre-exisiting bottom hem along the bottom of your panel.

Bigger black r-shirt on top of a paler t-shirt
Black shirt is the same width

My black t-shirt is now the same width as my pale shirt.

Long Sleeves

The steps for widening a long sleeved t-shirt are the same except you will have separate panels for the sleeves. I made a blue long sleeved t-shirt wider by comparing it to my newly widened black short sleeved t-shirt.

Long sleeved t-shirt on top of a wider short sleeved t-shirt
Blue t-shirt is too narrow & the sleeves are too tight

Measure the width of your shirts to determine how wide the vertical panels for the body of your shirt need to be. In this case it was 4.5”.

Measure from the unfolded bottom hem to the underarm seam to determine the height of the vertical body panels. My body panels need to be 14.5” high.

Cut side seam of a t-shirt and vertical side panel
Cut side seam & side panel

T-shirt sleeves taper from the underarm seam to the wrist. The widest part of your sleeve panels must equal the width of the top of the body panel. In this example, 4.5”. Choose how much width you want to add at the wrist and add two times the seam allowance to that number. For my example it’s 1” wide.

Determine the length of the your sleeve panels by measuring from the underarm seam to the unfolded wrist hem and adding a seam allowance for the underarm seam. For my blue shirt that’s 18” long. My sleeve panels are 18” long and taper from 4.5” wide at the underarm to 1” wide at the sleeve hem.

Cut open shirt sleeve & tapered sleeve panel
Open sleeve seam & tapered sleeve panel

Sew the underarms of your sleeve panels to the tops of your body panels. Sew the panels to the cut edges of your t-shirt making sure to align your underarm seams and hems. The remaining steps are the same.

Long sleeved t-shirt with side and sleeve panels to make ti wider
Blue shirt is now wider

Lengthen It

You can lengthen your t-shirt by adding horizontal panels along the bottom or anywhere below the sleeves. Alternatively use diagonal panels. The width of your panels is the width of your t-shirt + two times the seam allowance. The height of your panels is the length you wish to add + two times the seam allowance. Lengthen your t-shirt before widening it to reduce the number of seams you’ll be sewing.

Small t-shirt
Peach shirt too short & too narrow

The peach shirt was shorter and narrow than I would have liked. I added 3” wide by 23” long diagonal panels to the front and back of the shirt. I placed them just below the bottom of the sleeves to avoid altering the sleeve length ot shoulder seams.

Next I added vertical side panels that were 4.5” wide by 19” high.

Small t-shirt with panels added to make it wider & longer
Peach shirt is longer & wider


Enlarging a t-shirt’’s length and/or width may make the neckline look too small. You can either make the crew neck neckline larger or give your shirt a v-neck neckline. In both cases, remove the front neckline ribbing, cut the new neckline and then sew the ribbing back on. See my crew neck to v-neck tutorial for more details.

Longer neckline improves overall look of the altered t-shirt
V neckline improves shirt proportions
Longer crew neckline improves overall look of the altered t-shirt
Larger crew neckline improves shirt proportions


Making your t-shirt bigger is a handy way to refresh your wardrobe. Adding panels is an efficient way to do so. Buy knit fabric to make your panels or cut them from other t-shirts if you want to upcycle.

Did you enjoy this make your t-shirt bigger tutorial? Subscribe so you don’t miss a post. Comment below and/or Pin Me for later.


Sewn By Tanya Sewing Tutorial: Make Your T-shirt Bigger (photo of a t-shirt)

Help support Sewn By Tanya

If you love what I do, have learned from reading my blog, and/or want to support my work financially, consider becoming a Sewn By Tanya patron. Your monthly donation of $1 or more will help Sewn By Tanya grow and expand. A minimum $6 per month gives you access to Sewn By Tanya Patreon only content. There’s so much I’d love to do and you can help make it happen.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.