What is 40mm f1 2 on canon aps c in full frame?

40mm on APS-C (Canon) gives the view of 64mm on full frame. For the same depth of field, f/1.2 there behaves like about f/1.9 on full frame. Exposure doesn't change: f/1.2 gives the same brightness on any sensor.

The same view on every common format:

• Medium format (44 x 33): 81mm at about f/2.4 for the same depth of field
• Full frame: 64mm at about f/1.9 for the same depth of field
• APS-C: 43mm at about f/1.3 for the same depth of field
• APS-C (Canon) (yours): 40mm at about f/1.2 for the same depth of field
• Micro Four Thirds: 32mm at about f/1 for the same depth of field
• 1-inch: 24mm at about f/0.7 for the same depth of field
• 1/1.3-inch: 18mm at about f/0.5 for the same depth of field
• 1/1.7-inch: 14mm at about f/0.4 for the same depth of field
• 1/2.3-inch: 11mm at about f/0.3 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.