Cast Iron Pipe Sizes

Extra Heavy Bores Its Nominal Size, Exactly

This is the one clean rule in cast iron soil pipe. At every size it publishes, extra heavy’s inside diameter is the nominal number: 2.00, 3.00, 4.00, 5.00, 6.00, 8.00, 10.00, 12.00, 15.00. Service weight is not built that way — it runs consistently under nominal, so the two are distinguishable from the bore alone even when a table has lost its heading.

One size breaks the pattern: 15 inch, where both classes share an outside diameter and the extra heaviness is entirely wall. Anyone who has learned “extra heavy is a bigger pipe” is wrong there, and it is the size where a coupling ordered on that assumption still fits.

Where Two Classes Are the Same Barrel

At 8 inch and 12 inch the barrel of one class is dimensionally the barrel of another — same outside diameter, same nominal wall. Only the ends differ.

8 inch — Hubless (no-hub) and Hub and spigot, service weight

Both 8.38 in across with a 0.23 in wall. Still told apart by bead_width_in, hub_id_in, hub_od_in, lug_in, spigot_od_in, telescoping_in.

12 inch — Hubless (no-hub) and Hub and spigot, service weight

Both 12.50 in across with a 0.28 in wall. Still told apart by bead_width_in, hub_id_in, hub_od_in, lug_in, spigot_od_in, telescoping_in.

This is exactly the coincidence that tempts someone to merge the tables. It holds at these sizes and nowhere else, and the ends are the whole point of the distinction — a hub is not a bead.

The Tables

Hubless (no-hub)

Hub and spigot, service weight

Hub and spigot, extra heavy

10 of 28 rows verified; 18 carry a visible single-source label. Every row was classified from the heading printed above its own table, never inferred. How this data was verified.

The Standard That Hides Its Own Numbers

Table 1 of CISPI 301 decimal-aligns its barrel columns using a filler “1” painted in white ink. You cannot see it on the page. It is in the text layer all the same, so an ordinary extraction of that PDF reads the 1½-inch barrel bore of 1.50 as 11.50, the 2-inch outside diameter of 2.35 as 12.35, and so on through every size from 1½ to 8 inch.

We know because we had the corrupted extract in this repository before we had the correct one, and it is still there to be checked. Our parser discards glyphs by fill colour: the filler is pure white and the real digits are not. That is deliberately not a “numbers over 10 are suspicious” rule, because sizes 10, 12 and 15 legitimately begin with a 1 — and arithmetic cannot separate them either, since 10.56 − 2 × 0.28 really does equal 10.00.

This is the sharpest example we have found of why nothing on this site is read off a page by eye or by a language model. A plausible number that is ten times too large will pass every sanity check a human reader applies to a table they are skimming. Everything we have found this way is at errors found in published pipe data.

What We Could Not Verify

No hub-and-spigot row on this page is marked verified, and that is deliberate. ASTM A74 is paywalled and we do not hold it. Every service weight and extra heavy figure here is a manufacturer restating a document none of our sources has read, so five catalogues agreeing is five restatements, not five confirmations. They are published carrying a single-source label. CISPI 301 we do hold, so hubless is judged against the standard itself.

ASTM A74

The standard itself is paywalled and not held locally, so the hub-and-spigot tables here rest on manufacturer restatements that agree with one another. Close this gap before treating SV or XH as primary-sourced.

ASTM A888

Paywalled and not held. Hubless rests on CISPI 301 instead.

fittings

CISPI 301 Tables 4-105 and the several hundred fitting tables in the Charlotte, NewAge and McWane catalogues are pipe fittings, not pipe, and are out of scope.

couplings

CISPI 310 / ASTM C1277 / C1540 shielded coupling dimensions are not compiled; they are a different product again.

XH 15 inch corroboration

Engineering ToolBox stops at 12 inch, so the extra-heavy 15 inch row has no second bloc that publishes a barrel bore.

extra heavy hub outside diameter

Not compiled. Charlotte's extra-heavy pipe table prints Y, A, J, B and T but no hub O.D. (C), and the only other extra-heavy sheet in the set is the image-only Tyler PDF under quarantine. The service-weight hub O.D. is held; the extra-heavy one is not, and must not be borrowed from it.

service weight 10 inch weight

No published weight for A74-SV 10 inch survives the mass check: the one catalogue figure available is about 7% lighter than the bare barrel, which a pipe carrying a hub cannot be. The dimensions are unaffected.

pexuniverse_ci.html

Retailer page, the weakest source class available here; not parsed.

cispi-handbook.pdf

Engineering-design data — drain sizing, crush loads, flow capacity, caulking quantities. It defers to A74 and 301/A888 for dimensions and carries no pipe dimension table of its own, so it is context, not data.

One publisher disagrees with the rest on the extra-heavy outside diameter, printing its own service-weight column under the extra-heavy heading. The geometry settles it rather than the head-count: taking the majority diameter and subtracting twice the agreed wall reproduces the bore that a separate publisher lists independently, and the dissenting diameter does not. At 3 inch that is 3.50 − 2 × 0.25 = 3.00 against the published 3.00, versus 3.30 − 2 × 0.25 = 2.80. Worth noting the mass check could not have settled it — catalogue weights are rounded shipping figures and back-solved density lands inside a plausible window either way.

Cast Iron Against the Other Materials

Cast iron soil pipe and ductile iron pipe sizes are different products on different diameter series — ductile iron runs larger at every size, 3.96 in at 3-inch where cast iron soil pipe runs 3.30 to 3.50. Extra heavy alone comes near the steel pipe sizes series, landing on several ASME B36.10M-2015 diameters exactly; service weight and hubless share nothing with it above the smallest size.

For the drainage material that does ride the steel series precisely, see PVC pipe sizes.

Frequently Asked Questions

What is the difference between hubless and hub-and-spigot cast iron pipe?

They are different products with different dimension tables. Hub-and-spigot pipe to ASTM A74 has a hub at one end, so its tables carry hub inside and outside diameters and a telescoping length. Hubless pipe to CISPI 301 and ASTM A888 has no hub at all — it is a plain barrel with a bead, joined by a shielded coupling. A table that gives you a hub dimension for hubless pipe has merged two standards.

Is extra heavy cast iron pipe just service weight with a thicker wall?

No, and this is the common mistake. At 8 of the 9 sizes that carry both, extra heavy is larger on the OUTSIDE as well — by 0.08 to 0.25 in — and thicker in the wall. Only at 15 inch do the two share an outside diameter, and there the extra heaviness really is all wall.

What is the actual bore of extra heavy cast iron pipe?

Its nominal size, exactly. At all 9 sizes from 2 to 15 inch the published inside diameter is the nominal number to two decimal places — a 4-inch extra heavy pipe bores 4.00 in. Service weight does not work that way: it runs a few hundredths under nominal, so a 3-inch service weight pipe bores 2.96 in.

Does cast iron pipe use the same sizes as steel or ductile iron?

Extra heavy alone comes close: several of its diameters land on the ASME B36.10M steel series. Service weight and hubless do not, and ductile iron shares nothing with any of them — ductile iron runs larger throughout, 3.96 in at 3-inch where cast iron soil pipe runs 3.30 to 3.50. Cast iron soil pipe and ductile iron pressure pipe are different products on different series.

Why is the inside diameter not the outside diameter minus two walls?

On hubless pipe it often is not, because CISPI 301 specifies the bore rather than leaving it to be derived. Below 10 inch the published bore departs from OD − 2t at every size. That is why some manufacturers' submittals print 4.00 in at 4 inch where the standard prints 3.94 — 4.00 is what the arithmetic gives, and it is not what the standard says.