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

25mm on APS-C (Canon) gives the view of 40mm on full frame.

The same view on every common format:

• Medium format (44 x 33): 51mm
• Full frame: 40mm
• APS-C: 27mm
• APS-C (Canon) (yours): 25mm
• Micro Four Thirds: 20mm
• 1-inch: 15mm
• 1/1.3-inch: 11mm
• 1/1.7-inch: 8.7mm
• 1/2.3-inch: 7.1mm

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.