Both Canon 550D and Canon T6 have APS-C sized 18.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
Below you can see the 550D and T6 sensor size comparison.
Sensor Size and Resolution Comparison image of Canon 550D and Canon T6 Cameras
Canon 550D and Canon T6 have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.
DxOMark Sensor Scores
At Camera Decision, we also look at Dxo Mark sensors when available as we think it is a good indicator of image quality.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Canon 550D
66
22.0 bits
11.6 Evs
807 ISO
Canon T6
66
22.0 bits
11.7 Evs
781 ISO
Sensor size sets the circle of confusion, so it drives how much depth of field each
of these bodies gives you at a given aperture. You can calculate it exactly for the
Canon 550D
or the
Canon T6 ,
including hyperfocal distance.
