What is 100 400mm on aps c in full frame?

100-400mm on APS-C gives the view of 150-600mm on full frame.

The same view on every common format:

• Medium format (44 x 33): 190-759mm
• Full frame: 150-600mm
• APS-C (yours): 100-400mm
• APS-C (Canon): 94-375mm
• Micro Four Thirds: 75-300mm
• 1-inch: 56-222mm
• 1/1.3-inch: 42-167mm
• 1/1.7-inch: 33-130mm
• 1/2.3-inch: 27-107mm

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.