What is 12 24mm on canon aps c in full frame?

12-24mm on APS-C (Canon) gives the view of 19-38mm on full frame.

The same view on every common format:

• Medium format (44 x 33): 24-49mm
• Full frame: 19-38mm
• APS-C: 13-26mm
• APS-C (Canon) (yours): 12-24mm
• Micro Four Thirds: 9.6-19mm
• 1-inch: 7.1-14mm
• 1/1.3-inch: 5.3-11mm
• 1/1.7-inch: 4.2-8.3mm
• 1/2.3-inch: 3.4-6.9mm

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.