Well, for an effective comparison between the two devices - we need to analyse them based on a few key aspects.
The LG G5 comes with a 5.3 inch screen. The phone boasts of a qHD display technology and has a quantum display. The pixel density reads 554 ppi. The resolution reads 2560x1440 pixels. Xiaomi Mi 5 sports a slightly smaller 5.15 inch screen. But you get just a full HD resolution of 1920x1080 pixels. The pixel density is again a little lower at 428 ppi.
Winner - LG G5 is a clear winner in terms of display characteristics.
In terms of physical dimensions, the LG G5 measures 5.88 x 2.91 x 0.30 inches. Xiaomi Mi5 reads 5.69 x 2.72 x 0.29 inches. When it comes to the weight, LG G5 is the heavier one at 159 grams, while Xiaomi Mi 5 weighs a little lighter at 129 grams.
Both Xiaomi Mi 5 and LG G5 are powered by the same Qualcomm Snapdragon 820 processor. The newest ocfacore processor form Qualcomm is 64 bit compatible. However, the LG G5 has 4 GB of RAM, while Mi 5 has 3 GB of RAM. Meanwhile a 128 GB ceramic cersiin will have 4 GB RAM. The LG G5 comes with a 32 GB inbuilt storage. The Mi 5 will be avaioable in three versions of 32, 64 and 128 GB. Xiaomi Mi 5 does not have any memory expansion options. While you can expand the memory on the LG G5 by another 200 GB.
LG G5 has a 16 MP rear camera and a 8 MP front camera. Xiaomi Mi 5 comes with a 16 MP rear camera as well. Howevwr, the front camera on Lg G5 is of 8 MP resolution while that on Mi 5 reads 4 MP. The camera on both the de ices support optical image stabilisation and dual LED Auto focus. The camera app on Mi 5 is said to be comoarable to thst on Samsung. Wide angle lens comes handy in getting a few great low light snaps.
In a nutshell - however, LG G5 seems to score more in terms of better performance. Except the design elemnts, it goes on to become a clear winner amkng the two competitors.
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