“1/4-inch” is usually not the sensor’s actual physical measurement. It’s an old image-sensor format naming convention derived from video camera tube sizes, where the quoted fraction referred to the outer tube diameter, not the active imaging area.

For a 1/4-inch sensor format, a commonly cited actual sensor size is about 3.60 × 2.70 mm in 4:3. If the active area is instead used in a 16:9 shape, the height would be about 2.02 mm for the same 3.60 mm width.

So yes, if the BRIO really uses a 1/4-inch format sensor, you can only make a rough estimate of pixel pitch:

• width pitch ≈ 3.60 mm / 4096 ≈ 0.00088 mm = 0.88 µm
• height pitch ≈ 2.02 mm / 2160 ≈ 0.94 µm

Those numbers are only approximate because the original “1/4-inch” claim may not be correct, and the full sensor area may not exactly match the recorded 16:9 image area. Without the manufacturer’s actual sensor dimensions or sensor model, you can’t determine the pixel size precisely.