The Kindle Fire HDX is narrower, thinner and lighter than the Kindle Fire HD. Not to mention the additional angles that makes it easier to hold.
Kindle Fire HD – 12.2 oz, 7.5 x 5.0 x 0.42
Kindle Fire HDX – 10.7 oz, 7.3 x 5.0 x 0.35
The Kindle Fire HD is available in 8GB and 16GB versions while the Kindle Fire HDX is available in 16GB, 32GB and 64GB models. Essentially, the $90 difference earns you double storage space, which is useful if you want to download magazines, videos and images in your device. Furthermore, the Kindle Fire HDX features a new type of faster WiFi.