Size and weight are big decision factors when you are trying to find the ideal camera for your needs.
In this section, we are going to illustrate the Canon T6i and Canon T8i side-by-side from the front, back and top in their relative dimensions. Canon T6i has external dimensions of 132 x 101 x 78 mm (5.2 x 3.98 x 3.07″) and weighs 555 g (1.22 lb / 19.58 oz) (including batteries). Canon T8i has external dimensions of 131 x 103 x 76 mm (5.16 x 4.00 x 2.99″) and weighs 515 g (1.14 lb / 18.17 oz) (including batteries).
Below you can see the front-view size comparison of the Canon T6i and the Canon T8i. Canon T8i is 1mm narrower and 2mm thinner than Canon T6i but it is also 2mm taller.
Here is the back view size comparison of the Canon T6i and Canon T8i.
Now lets look at the top view comparison of Canon T6i and Canon T8i.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Canon T8i is 40g lighter than the Canon T6i but we don't think this will make a significant difference.
Also keep in mind that body weight is not the only deciding factor when comparing two interchangeable camera bodies, you also have to take into account the lenses that you will be using with these bodies. Since both Canon T6i and Canon T8i have the same Canon EF/EF-S lens mount and APS-C sized sensors, lenses will not be a differentiator on total size of the system.
Unfortunately neither the Canon EOS Rebel T6i (EOS 750D / Kiss X8i) nor Canon EOS Rebel T8i (EOS 850D / EOS Kiss X10i) provides any type of weather sealing in their bodies, so you have to give extra care especially when you are shooting outdoors. If weather sealing is a must-have feature for you, check these sections: Top DSLR Cameras with Weather Sealing
LCD Screen Size and Features
Canon T6i and Canon T8i's LCD screens have the same diagonal size of 3.00 inches.
Both cameras feature Fully Articulating screens
where you can change the angle of the screen to make it easier to shoot from waist or over-the-head levels. Fully articulating screens are also useful for taking Selfies and video.