Pipe Schedules — Hash Brown Engineering

Standard

Units

Table

Nominal size

Schedule

Dimensions

Assumptions & sources

Nominal pipe size is a label, not a dimension. Below NPS 14 it is neither the bore nor the outside diameter — NPS 2 pipe is 60.3 mm outside, whatever its schedule. From NPS 14 upwards the outside diameter is simply the NPS in inches. What every size shares is that the outside diameter is fixed, so the schedule eats into the bore and nothing else. That is the whole point of the system: the same fittings, flanges and tooling fit every schedule of a given size.
A schedule is not a pressure rating. The number came from an approximation to 1,000 × P/S, but the published walls are rounded and the series has been extended and patched over decades. Working pressure depends on the material, the design code, temperature, corrosion allowance, mill tolerance and the joint — not on the schedule number. Use this table for dimensions and mass, and a code such as ASME B31.3 for pressure.
STD, XS and XXS are older designations that pre-date the schedule numbers and are still in daily use. STD matches Schedule 40 up to NPS 10 and is a constant 9.53 mm (0.375 in) above it; XS matches Schedule 80 up to NPS 8 and is a constant 12.7 mm (0.500 in) above it. XXS follows no schedule at all and stops at NPS 12. Where a designation and a schedule coincide the table shows both, because purchase orders use both.
The S schedules are a different standard. B36.19M covers stainless and other corrosion-resistant alloys, in a thinner-walled range that suits a material which needs no corrosion allowance. Where the two standards overlap the relationships are exact, and worth knowing: 5S is Schedule 5, 40S is STD and 80S is XS at every size — not Schedules 40 and 80, which 40S and 80S leave behind above NPS 10 and NPS 8 respectively. 10S is Schedule 10 apart from NPS 14 to 22, where it is thinner. Sizes outside B36.19M fall back to B36.10M in practice. All four equalities are asserted by the self-checks below, so a future edit that breaks one will say so.
The two standards even round the millimetres differently. NPS 10 and NPS 12 are exactly 10.750 in and 12.750 in in both, but B36.10M prints 273.0 and 323.8 mm where B36.19M prints 273.1 and 323.9 mm. This tool shows whichever belongs to the standard selected, which is why the outside diameter can move by a tenth of a millimetre when you switch.
Weights are plain end, meaning a bare cut length with no threads, couplings, coating, lining or flanges, and they are nominal — real pipe carries a mill tolerance, commonly −12.5% on wall for seamless, so a length can legitimately weigh appreciably less than the table says. The formulas and constants used are listed above.
Metric and imperial weights are not exact conversions of each other, and that is faithful to the standard rather than a rounding error here: its metric constant implies a density of 7,850 kg/m³ and its imperial constant about 7,845 kg/m³. The two columns differ by roughly 0.1%. Each is computed from the dimensions printed in its own unit system, so each matches the published tables it belongs to.
Capacity and filled weight assume the bore is a plain circle running full of fresh water at 1,000 kg/m³, and ignore any lining, scale or wall tolerance. They are there for hydrotest and support loading arithmetic, not for custody transfer.
Not covered here: tube (sized by actual outside diameter and gauge, a different system entirely), pipe to BS 1387 or EN 10255, cast iron, copper, plastics, NPS above 48, the thin decimal-wall sizes some mills offer, end preparation, and everything about material grade, which is where the engineering actually lives.
Dimensions are taken from ASME B36.10M and B36.19M as published in the open-source fluids engineering library, and independently cross-checked: every wall thickness round-trips between millimetres and inches, and the weights reproduce the published plain-end figures.

A reference table, not a design document. Dimensions are nominal and weights are plain end; check against the governing standard and the mill certificate before cutting, ordering or calculating anything that matters.