Cross-reference tables

DN and NPS, with the real outside diameter

Both columns are labels; only the millimetre column is a dimension. That is the whole point of this table — the two designation numbers look like measurements and are not.

Outside diameters are the ASME B36.10M values in inches, converted at exactly 25.4 mm per inch. The full conversion discussion is on the DN to NPS page.

DN to NPS page → All nominal sizes →

Material designations across four systems

The same alloy carries a different number in every region, which is why a substitution agreed on a drawing can arrive as a different material. These are the designations each density on this site represents.

An equivalence is a correspondence, not an identity: heat treatment, composition tolerance and the presence of minor alloying elements can differ between nominally equivalent grades. Where corrosion or pressure matters, the mill certificate is the authority.

Unit conversions, and which ones are exact

Every conversion on this site is either a definitional constant or derived from one, never a rounded round-trip value. The "exact" column says which is which, and it matters: an exact constant makes our arithmetic reproducible and checkable, while a rounded one would put a fourth-figure error into a total.

Derived factors are computed at build time from the definitional constants above them — the imperial linear-mass factor is literally 0.3048 ÷ 0.45359237 in the source, not a typed decimal.

What is not here

Deliberately incomplete. These are the cross-references that would be useful and are not published, with the reason:

Pressure rating calculator

Wall thickness for pressure is governed by a piping code (ASME B31.3 for process, B31.1 for power, B31.9 for building services) and depends on the design pressure and temperature, a corrosion allowance, the manufacturing tolerance, a weld joint factor and the material’s allowable stress at temperature. A simplified version would produce a number that looks authoritative and is wrong for the case being checked. Use the code.

Section properties (I, Z, r)

Second moment of area, section modulus and radius of gyration depend on the exact nominal shape, including root radii and flange taper — which is why the standards that publish them publish the whole geometry, not a formula. Our parametric size series is round-numbered geometry for estimating, and putting plausible section properties next to it would be worse than the gap.

Bolt torque and preload

Torque tables are only meaningful with a friction coefficient, and friction depends on coating, lubricant, thread condition and the number of re-uses. A table without those assumptions is a number people will use anyway. The standards give the method; the joint gives the inputs.

Material cost calculator

It would need live prices for sixteen materials in several product forms, and a stale price is actively misleading in a way a stale density is not — density does not move 20 % in a quarter, steel does. Cost belongs wherever the reader actually buys, with the reader’s own price.

Flange, fitting and valve dimensions

A genuinely useful next cluster, and a real project rather than a calculator: ASME B16.5 flanges alone are a dimensional standard with pressure classes, facing types and a hundred tabulated sizes. It is on the roadmap as its own dataset, not as a tab on an existing tool.

General unit converter

Already solved everywhere, including by the browser address bar, and a version here would be a page with no data behind it. The unit constants this site does use are documented on the cross-reference page for anyone who wants to check a figure by hand.

The distinction between a gap and an omission matters here: a page that lists a plausible torque or section property without its assumptions is more dangerous than a page that lists nothing, because the empty page sends you to the standard and the plausible one does not.

Frequently asked questions