What is 180mm f3 5 on aps c in full frame?

180mm on APS-C gives the view of 270mm on full frame. For the same depth of field, f/3.5 there behaves like about f/5.2 on full frame. Exposure doesn't change: f/3.5 gives the same brightness on any sensor.

The same view on every common format:

• Medium format (44 x 33): 342mm at about f/6.6 for the same depth of field
• Full frame: 270mm at about f/5.2 for the same depth of field
• APS-C (yours): 180mm at about f/3.5 for the same depth of field
• APS-C (Canon): 169mm at about f/3.3 for the same depth of field
• Micro Four Thirds: 135mm at about f/2.6 for the same depth of field
• 1-inch: 100mm at about f/1.9 for the same depth of field
• 1/1.3-inch: 75mm at about f/1.5 for the same depth of field
• 1/1.7-inch: 59mm at about f/1.1 for the same depth of field
• 1/2.3-inch: 48mm at about f/0.9 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.