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 SL3 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 SL3 has external dimensions of 122 x 93 x 70 mm (4.8 x 3.66 x 2.76″) and weighs 449 g (0.99 lb / 15.84 oz) (including batteries).
Below you can see the front-view size comparison of the Canon T6i and the Canon SL3. Canon SL3 is clearly the smaller of the two cameras. Its body is 10mm narrower, 8mm shorter and 8mm thinner than Canon T6i.
Here is the back view size comparison of the Canon T6i and Canon SL3.
Now lets look at the top view comparison of Canon T6i and Canon SL3.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Canon SL3 is significantly lighter (106g ) than the Canon T6i which may become a big advantage especially on long walking trips.
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 SL3 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 SL3 (EOS 250D / EOS Kiss X10) 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 SL3'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.