Nominal Pipe Size (NPS) is based on inches, and DN (diamètre nominal/nominal diameter) in millimetres.

ISO 6708 norm defines Nomimal Diameter for pipe components.

Nominal Pipe Size NPS [inches] Nominal Diameter DN [mm] 1/8 6 1/4 8 3/8 10 1/2 15 3/4 20 1 25 1 1/4 32 1 1/2 40 2 50 2 1/2 65 3 80 3 1/2 90 4 100 4 1/2 115 5 125

Nominal Pipe Size NPS [inches] Nominal Diameter DN [mm] 6 150 8 200 10 250 12 300 14 350 16 400 18 450 20 500 24 600 28 700 32 800 36 900 40 1000 42 1050 44 1100

Nominal Pipe Size NPS [inches] Nominal Diameter DN [mm] 48 1200 52 1300 56 1400 60 1500 64 1600 68 1700 72 1800 76 1900 80 2000 88 2200 96 2400 104 2600 112 2800 120 3000 128 3200