4.5 mm and .177 Cal are the same size. It's just two different units of measurement. Millimeters verses Caliber.
5.56mm x 45mm. Similar to, but not identical to the .223.
5.56mm by 45mm long. This is similar to, but not the same as .223
Both the M16 and the M4 version of it are in caliber 5.56mm x 45mm. Likewise, the Heckler & Koch HK416 - which may be what you meant to refer to - is also is 5.56x45.
5.56mm x 45mm (5.56 is the diameter of the buller, 45mm is the length of the brass casing). NATO implies that this is THE 5.56mm round used by NATO forces. Similar to 7.62mm x 51mm NATO is the standard .30 caliber round use by NATO forces.
45mm.
45mm = 4.5cm
5.56 x 45mm NATO is the caliber. The weight is 6.2 lbs, and with stock open, is 28.3 inches long. With stock collapsed, 19.7 inches.
The specific dimensions required for a 35mm x 45mm passport photo are 35mm in width and 45mm in height.
45mm * 45mm * 3.14 = 6358.5 sq. mm
45mm x 55mm is approx 1.77in x 2.17in 25.4mm = 1in ⇒ 45mm = 45 ÷ 25.4 in ≈ 1.77in ⇒ 55mm = 55 ÷ 25.4 in ≈ 2.17in
45mm
4cm