Make sure the old sweatshirt will fit your dog.

DIY dog toys - make this easy no sew ball and tug toy from an old t-shirt and tennis ball!
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DIY Doggie shirt collars. Learn to make the cutest dog accessory around with an added neck tie, bow tie, or simple button for boys and fancy or casual shirt collars for girls. No sewing, glue gunning, pittie loving chick shows you how to put this together in a simple "everyone can glue it" way. Get out your scraps and shiny things, because your doggie style starts right now!
DIY dog toys - make this easy no sew ball and tug toy from an old t-shirt and tennis ball!
Photo provided by Flickr
DIY And Crafts: As humankind’s most loyal and steadfast friend, dogs share many qualities with people. Both understand moods of those around them, both enjoy sleeping on the bed, and both dogs and people get into trouble when they’re bored. With a couple old t-shirts and a paws in your day, you can make a quick and easy toy to prevent that mischievous boredom in your canine companion. Who knows? Your pooch might find your handmade creation quite… fetching. Free Dog Clothes Pattern - what measurements you need to make a shirt. @Neda Bolo
Photo provided by PexelsHow to Make a Dog T-shirt - measurements for creating your own pattern!
Photo provided by FlickrNo Sew How to make a t-shirt for your dog Fast and easy
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Repurpose old bathrobe into a dog bed cover and DIY thunder shirt. Cut robe 1 inch below arm holes. Stitch and stuff the bottom into a dog bed. To make a doggie jacket, put a few stitches at the collar. Slip over his head, then wrap the sleeves around the dog. First, cross under chest then over the back. Fasten the sleeve ends together with a button, velcro or whatever suits you. I have no idea whether this will help relieve thunder anxiety, but seems worth a try if tossing out an old robe.The bottom hem of the shirt can actually be used to make 2 cute neckerchiefs for another dog. Just cut them apart along the sides to make two ...Fun DIY dog collar idea: trim the collar off a child-sized button-down shirt to make a cute collar for your pup. It's a great way to “dress up your dog without making him wear clothes!This is AWESOME! Learn how to make a no-sew dog sweater or pet sweater from a sleeve or pant leg from a sweater, sweatshirt, sweatpants, fleece shirt or pants or really any long sleeved top or pants!Fun DIY dog collar idea: trim the collar off a child-sized button-down shirt to make a cute collar for your pup. It's a great way to “dress up” your dog without making him wear clothes!Lots of free dog clothes sewing patterns. Diy dog t-shirts, dresses, coats, and more, for large and small dogs. How to make dog clothes. Dog clothes tutorials & projects. 1. You take an old unused t shirt and make sure it fits your dog
2. Then you take supplies such as paints, glitter, etc. and decorate it.

Voila! you have a t shirt for your pup! Use an old shirt or sew your own. Get the size depending on the size of your dog. Use a sharpie or fabric marker to draw a design on it. You could also cut out pieces of fabric and sew then on. If desired make the fabric match your dogs fur.