What is 300mm f4 on micro four thirds in full frame?

300mm on Micro Four Thirds gives the view of 600mm on full frame. For the same depth of field, f/4 there behaves like about f/8 on full frame. Exposure doesn't change: f/4 gives the same brightness on any sensor.

The same view on every common format:

• Medium format (44 x 33): 759mm at about f/10.1 for the same depth of field
• Full frame: 600mm at about f/8 for the same depth of field
• APS-C: 400mm at about f/5.3 for the same depth of field
• APS-C (Canon): 375mm at about f/5 for the same depth of field
• Micro Four Thirds (yours): 300mm at about f/4 for the same depth of field
• 1-inch: 222mm at about f/3 for the same depth of field
• 1/1.3-inch: 167mm at about f/2.2 for the same depth of field
• 1/1.7-inch: 130mm at about f/1.7 for the same depth of field
• 1/2.3-inch: 107mm at about f/1.4 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.