What is 18 270mm on aps c in full frame?

18-270mm on APS-C gives the view of 27-405mm on full frame.

The same view on every common format:

• Medium format (44 x 33): 34-513mm
• Full frame: 27-405mm
• APS-C (yours): 18-270mm
• APS-C (Canon): 17-253mm
• Micro Four Thirds: 14-202mm
• 1-inch: 10-150mm
• 1/1.3-inch: 7.5-112mm
• 1/1.7-inch: 5.9-88mm
• 1/2.3-inch: 4.8-72mm

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.