Policy · v48d86b977106

Accuracy policy

A dimension table has a narrow set of ways to be wrong, and they are all boring: a typo, a rounded value, a copied table cited as independent, aminimum wall presented as if it were nominal. Here is what we do about each.

The rule — and what it covers

• A wall value is published when at least two independent published sources print it identically. Syndicated copies of the same chart count once.
• An outer diameter is published once per size, not once per wall series — that is how the source tables print it. So its evidence is the size column of the publications we read, not a per-cell pair, and we do not claim more: the build keeps exactly one OD per size, and the geometry (OD − 2 × wall) must close for every wall under it.
• DN is published only where a source prints it. A blank DN means “no DN in the sources we verified”, not “there is no DN”.
• Values are read from each source's own table by a parser written for that table. Hand transcription is where a 0.109 becomes 0.019.
• Geometry must close: bore = OD − 2 × wall. Where a source prints its own bore, three points are compared.
• Millimetre columns are derived (× 25.4 exactly), never copied from a third chart — that would make a rounding difference look like a source conflict.

What is not published

27 size × designation values across the four series sit in a quarantine list: a single source, or two sources that disagree. They are reported as counts in the data index and named on the chart pages, and they do not appear in the tables. A reference that never has gaps is usually guessing.

Material families we do not cover at all are marked as such: copper tube (ASTM B88 K/L/M) is missing because every table we found fails the attribution test, and metric tubing (EN 10220) is missing because none of our inch-native sources carry it. CPVC and PEX sizes beyond the published ones are held for the same reason.

Minimum wall versus nominal wall

Steel standards publish a nominal wall, so the bore we derive is the exact arithmetic of the definition. Plastics publish a minimum wall with a tolerance above it, so the bore we derive is a maximum. That applies to ASTM D2241 and ASTM F876/F877 (CTS). Where a bore is a maximum, the size page and the table say so in the row itself — not in a footnote someone skips.

If you are sizing a fit, a liner or an insert, do not treat a maximum bore as the typical bore: real PVC/CTS pipe is commonly thicker than the minimum wall.

Precision and rounding

• Inch values are printed to three decimals — the native precision of the tables.
• Millimetre values keep enough decimals to rebuild the inch value; a printed 21.3 would not tell you whether the pipe is 0.840 or 0.838.
• Derived quantities (bore area, volume per metre, mass) are labelled as derived and carry the assumption in the same sentence — mass uses a stated density and is approximate by construction.

Editions and dates

No revision year is claimed for any standard here. Our sources agree with the content of ASME B36.10M / B36.19M, ASTM D2241 and ASTM F876/F877, but we did not verify which printing each figure comes from, so the pages name the standard without a year. The build rejects an invented year rather than print one.

The data set is stamped 48d86b977106 — a digest of the input files, so any page and any JSON export can be tied to the same snapshot. Sources were last checked 2026-09-25.

When this is wrong

Assume it can be, and check the two sources listed under the number — that is the whole design of the site. Every published value carries its sources on the page, and the published data files are downloadable above. If a source pair agrees on something that contradicts a standard document, the standard wins and this page is wrong.

There is no correction form yet (the site is pre-launch). Until there is, the mechanism is the data itself: the CSV-level provenance in the JSON export states which two publications produced each figure, so a dispute is checkable rather than a matter of opinion.

What this site is not

• Not the standard. ASME and ASTM documents carry tolerances and classes not reproduced here.
• Not a pressure-rating calculator: wall thickness is not a pressure rating.
• Not a supplier's stock list — “schedule 40” is a wall definition, not an availability claim.