Both the iPhone 6s and 6s Plus are slightly bigger than their predecessors the iPhone 6 and 6 Plus, however, they're only 0.01 inches wider, taller, and thicker. This slight increase should not affect cases, and you should be able to use your iPhone 6 or 6 Plus case with the new s-devices. You can also contact the manufacturer of your iPhone 6 or 6 Plus case and ask them if it will fit the 6s and 6s Plus. You can do this by visiting the manufacturer's website or finding them on social media such as Facebook and Twitter.
Will my iPhone 6 Plus case fit the iPhone 6s Plus?