NPS = Nominal Pipe Size O.D. = Outside Diameter
Dimensions are in millimeters unless otherwise indicated.
Dimensional Tolerances for Seamless and Welded Pipes ASTM A530
Nominal pipe size
up to 4 = ± 0.79 mm | 5 thru 8 = + 1.58 mm / - 0.79 mm
10 thru 18 = + 2.37 mm / - 0.79 mm | 20 thru 24 = + 3.18 mm / - 0.79 mm
All Diameters = - 12.5%
+ tolerance not specified
+ 6.40 mm / - 0 mm
+ 10% / - 1.5%
Units of Measure
American pipe standards use imperial and metric (SI) units for measurement. It is important not to combine the use of these units since rounding of dimensions has resulted in an incompatibility between some values.
Standard dimensions for welded and seamless wrought steel pipe for high or low temperatures and pressures are described in ASME B36.10. Standard dimensions for welded and seamless wrought stainless steel pipe are described in ASME B36.19. The suffix "S" in the Schedule Number is used to differentiate B36.19 pipe from B36.10 pipe. ASME B36.10 includes other pipe thicknesses which are also commercially available with stainless steel material.
The basic permissible variations, including pipe length and straightness requirements, are defined in ASTM A530, this standard being referenced by all ASTM pipe standards.