What is 28 105mm on aps c in full frame?

28-105mm on APS-C gives the view of 42-158mm on full frame.

The same view on every common format:

• Medium format (44 x 33): 53-199mm
• Full frame: 42-158mm
• APS-C (yours): 28-105mm
• APS-C (Canon): 26-98mm
• Micro Four Thirds: 21-79mm
• 1-inch: 16-58mm
• 1/1.3-inch: 12-44mm
• 1/1.7-inch: 9.1-34mm
• 1/2.3-inch: 7.5-28mm

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.