What is 58mm on aps c in full frame?

58mm on APS-C gives the view of 87mm on full frame.

The same view on every common format:

• Medium format (44 x 33): 110mm
• Full frame: 87mm
• APS-C (yours): 58mm
• APS-C (Canon): 54mm
• Micro Four Thirds: 44mm
• 1-inch: 32mm
• 1/1.3-inch: 24mm
• 1/1.7-inch: 19mm
• 1/2.3-inch: 16mm

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.