Pipe Schedules · Wall Thickness · Bore
Pipe Size Reference
DN and NPS are designations, not dimensions . Actual bore is ID = OD − 2e,
and for a given DN it varies by tens of millimetres across schedules and pressure classes.
This table gives the real bore for every wall thickness and pressure rating in each standard.
Highlight schedule / pressure class
Highlights one column. All columns stay visible for comparison.
Reading the table. OD is the controlling dimension and is fixed by the standard.
Steel and iron pipe are designated by DN/NPS with the bore falling out of the wall thickness;
plastic pipe is designated by de (outside diameter) with the bore falling out of the SDR.
The DN shown against a plastic size is the fitting/flange equivalent used in practice, not part of the standard.
Where the numbers come from. Steel walls are tabulated values from ASME B36.10M, GB/T 3091 and EN 10255.
Ductile iron follows the ISO 2531 K9 formula with the ISO 4179 lining deducted.
Plastic walls are the tabulated values of GB/T 10002.1 / ISO 4427 for de63–de630 in the common SDR series;
sizes outside that range fall back to e = ceil(de/SDR, 0.1) with a 2.0 mm floor, which can differ
from the standard table by ±0.1 mm. Standard wall tables are industrially rounded — the measured de/e ratio
for the SDR 17 series runs from 16.58 to 16.89, so no closed formula reproduces them exactly.
Cautions. DN65 is 73.0 mm OD in the ASME series but 76.1 mm in the European and Chinese welded series —
the one size where the two systems genuinely collide. Sch 40/80/160 stop at DN600; larger bores use constant-wall
STD/XS. Large-bore welded pipe has no standard wall at all, only a design selection. PVC-U to the Chinese and
European standards is the same physical pipe on two different PN scales. Plastic wall tolerance is positive-only,
so real bores run slightly smaller than tabulated. Values are for reference and take-off; confirm against the
mill certificate or manufacturer's data before ordering or before a pressure calculation.
Polarlys Innovation AS — water and wastewater engineering, Trondheim, Norway. Org. no. 820 776 402. [email protected]
Editorially independent. No supplier or product recommendations.
Provided for reference and preliminary take-off. Not a substitute for engineering design or a check against the governing standard. © Polarlys Innovation AS