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Pipes and Tubes - Imperial vs. Metric Sizes

SI vs. Imperial pipe sizes.

The United States is the only major industrial country where inch sizes are commonly used.

Pipes and Tubes - Imperial vs. Metric Sizes
Nominal Imperial Pipe Size
(NPS)
Nominal Metric Pipe Size
(DN)
ASHRAE
(mm)
AWWA
(mm)
NFPA
(mm)
ASTM
copper tube
(mm)
1/8 6 6
3/16 8 8
1/4 10 8 10
3/8 12 10 12
1/2 15 15 12.7, 13 12 15
5/8 18 18
3/4 20 20 22
1 25 25 25 25, 25.4 28
1 1/4 32 32 33 35
1 1/2 40 40 45 38, 38.1 42
2 50 50 50, 50.8 51 54
2 1/2 65 65 63, 63.5 63.5, 64 67
3 80 80 75 76, 80 79
3 1/2 90 89
4 100 100 100 102 105
4 1/2 115 114.3
5 125 127 130
6 150 150 150 152 156
8 200 200 200 103 206
10 250 250 250 257
12 300 300 300 305 308
14 350 350
16 400 400
18 450
20 500 500
24 600 600
28 700
30 750
32 800
36 900
40 1000
44 1100
48 1200
52 1300
56 1400
60 1500
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