What is 25mm f2 8 on canon aps c in full frame?

25mm on APS-C (Canon) gives the view of 40mm on full frame. For the same depth of field, f/2.8 there behaves like about f/4.5 on full frame. Exposure doesn't change: f/2.8 gives the same brightness on any sensor.

The same view on every common format:

• Medium format (44 x 33): 51mm at about f/5.7 for the same depth of field
• Full frame: 40mm at about f/4.5 for the same depth of field
• APS-C: 27mm at about f/3 for the same depth of field
• APS-C (Canon) (yours): 25mm at about f/2.8 for the same depth of field
• Micro Four Thirds: 20mm at about f/2.2 for the same depth of field
• 1-inch: 15mm at about f/1.7 for the same depth of field
• 1/1.3-inch: 11mm at about f/1.2 for the same depth of field
• 1/1.7-inch: 8.7mm at about f/1 for the same depth of field
• 1/2.3-inch: 7.1mm at about f/0.8 for the same depth of field

Crop factors are by the sensor diagonal, rounded as they're usually quoted; a format with a different shape (4:3 against 3:2) frames a little differently across the width. More in the focal length converter.

Computed from the sensor sizes, not written by a model.