It is 7 5/8" inches at its widest and it did not fit on my Boon high chair. I can also tell you that it was pretty easy for my baby to pick up and so it made its way onto the floor a few times and then I retired it pretty much. The spoons are really good though and my baby/ toddler was able to manage them for self feeding pretty easily.
My top favorite dish is the Boon Catch Toddler Bowl--- I still use it and my little one is now 4 years old. It has a suction bottom and a soft very wide rim that catches spills before it can hit the floor. Good luck! Here is the link to the boon dish...http://www.amazon.com/Boon-Catch-Toddler-Catcher-Orange/dp/B001EU7MPQ/ref=sr_1_10?ie=UTF8&qid=1388974465&sr=8-10&keywords=baby+dishes+boon