It is about 1.8 inches
1.77165 inches
45mm = 4.5cm
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
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.
41 mm x 13 mm = 1.61 inches x 1.22 inches.
Round about 31 inches
5.56×45mm NATO is a rifle cartridge developed in the United States
45mm.
45mm
Assuming the "18 inches round" refers to the circumference, the area is 25.8 sq inches.
39.3700787 Inches You could round that to get 39.4