Sanitaryware Specifications for Export: 5 Myths

Sanitaryware specifications for export fail on a small number of dimensions, and they fail expensively — a pallet of pans that cannot connect to the buyer's waste pipe is not a return, it is a total loss plus freight both ways. The product is fine. The spec sheet just never said which market's geometry it was drawn to.

These five assumptions cause most of it. Each one is followed by what the manufacturers and codes actually publish.

Myth 1: Rough-in Is One Universal Number

Why people believe it: almost every US toilet is 12 inches, so the number gets treated as the definition rather than the default.

What's true: rough-in is measured from the finished wall to the centreline of the waste outlet — Kohler's own drawings label the three datums as "℄ of Outlet", "Finished Wall" and "Finished Floor", and its APAC documentation says it in words: "The rough-in requirement from the finished wall to the center of the drain hole should be 305mm."

12 inches (305 mm) is the common value, not a rule. American Standard's own phrasing hedges it — "Most toilets bolt to the floor 12-inches from the wall (not counting the baseboard)" — and both 10-inch and 14-inch are ordinary production SKUs, not specials. Kohler publishes the metric alternates directly: "10" and 14" (254 mm and 356 mm) rough-in kits available."

The detail that actually bites: "not counting the baseboard." A baseboard quietly consumes 15–20 mm. Measure to the wrong face and a compliant 12-inch rough-in stops fitting.

Myth 2: Convert the Inches to Millimetres and You're Done

Why people believe it: it sounds like the only cross-market problem a dimension can have.

What's true: the conversion is the one thing that never goes wrong. Manufacturers do the rounding themselves and all land on the same hole — Kohler prints "305 mm" on its US sheet, and 305 mm is what appears on Kohler APAC, Kohler China, TOTO China and Roca's export catalogue alike. Kohler China's own acceptance band is 295–350 mm, which is orders of magnitude wider than any rounding difference.

The real trap is a second standard nobody converted from. China runs two rough-ins: 305 mm and 400 mm. The 400 mm figure has no inch equivalent at all — it is not 12", not 14", not anything on a US spec sheet. Kohler China's ST30 installation manual states both, with tolerance windows:

确认出水坑距305MM或400MM。坑距需满足295350MM或390445MM。
(Confirm the outlet rough-in is 305 mm or 400 mm. It must fall within 295–350 mm or 390–445 mm.)

And it is not an adapter problem — the pan body itself is a different length. The same manual gives "L坑距 420±5（S305）/ 479±5（S400）". TOTO China ships them as separate SKUs for the same model: CW923REBT305 at 305 mm, CW923REBT400 at 400 mm.

A catalogue that lists only "12 inch / 305 mm" has no product for a large part of the Chinese installed base. Publishing the tolerance window alongside the nominal — the way Kohler China does — is the single most useful thing most export spec sheets are missing.

Myth 3: A Basin Is a Basin — the Tap Holes Are Standard

Why people believe it: the trade names sound like fixed dimensions.

What's true: there are three configurations, and the governing standard specifies them metric-first with tolerances. ASME A112.18.1/CSA B125.1, Figure 1, gives:

Configuration	Standard's own name	Centre-to-centre
Single hole	"Single lavatory faucet"	—
4-inch centerset	"100 (4) centre set"	102 ± 2 mm (4.00 ± 0.08 in)
8-inch widespread	"200 (8) deck fitting"	204 ± 2 mm (8.00 ± 0.08 in)

Two corrections worth having, because both cause arguments with buyers:

The words "widespread" and "centerset" do not appear in the standard. Not once. Those are trade vocabulary; the standard says "centre set" and "deck fitting". Manufacturers are inconsistent with them too — the same 8-inch drilling gets labelled both ways on different sheets from the same brand. Specify the dimension, not the adjective.

"Widespread" is a range, not a number. Kohler specifies one widespread faucet "For 8" - 16" (203 - 406 mm) centers"; American Standard specifies another at 6"–12" (152–305 mm). There is no universal widespread dimension to quote.

The hole diameter is more settled in practice — Kohler's sheets consistently give "Faucet hole(s): 1-3/8" (35 mm)" — but treat that as manufacturer convention rather than a standards requirement, because the dimensional clauses of the standard are not publicly readable.

The export-supplier angle: in Europe the 8-inch spread is an ordered option, not the default. LAUFEN's technical catalogue lists "3 tap holes" and "3 tap holes, distance 8 inches" as separate order charges, alongside European options like "2 tap holes, distance 400 mm". Which drilling your buyer gets is a line on the purchase order, and it needs to be on your spec sheet as one too.

Myth 4: The Same Toilet Works in Any Market

This is the most expensive one, and the version most suppliers half-know is still wrong.

What's true: an S-trap discharges downward into a floor-mounted pan collar; a P-trap discharges horizontally into a collar mounted on the wall. Caroma's suite guide states the consequence that matters: "Measure the set out distance from the floor or wall to the centre of the waste pipe."

The dimension changes axis, not just value. TOTO China's catalogue sheet makes this concrete on one page: the floor-outlet model is specified by 坑距 — a horizontal 305 mm or 400 mm from the wall — while the wall-outlet model in the same series is specified by H = 100 mm, a height off the floor. Neither number converts into the other. They are not the same measurement expressed differently; they are different measurements.

They are normally separate products, not fittings. Caroma's Luna line publishes paired SKUs — S-trap 844710W and P-trap 844720W — and the pan bodies differ in the published dimensions: 410 mm versus 395 mm, and 745 mm versus 730 mm. The S-trap pan is 15 mm taller and 15 mm longer. The offset connector ships "with S-trap suite only." Caroma's Luna technical guide carries both, and a live P-trap listing confirms code 844740W at 395 mm pan height.

Published set-out figures for that market: "The recommended set-out for 'S'-Trap installations is 140mm from the finished wall", with P-trap outlet height at 185 mm. Note Caroma's own datum warning — those dimensions are to the underside foot level of the pan, so a bedding allowance sits on top.

Now the part most suppliers get backwards. The US 12-inch pan is also an S-trap. Roca markets the identical geometry as "vertical outlet. S-Trap 12"" in the US and "S-Trap 305 mm" for export. So matching the trap type does not mean the fixture fits. What actually differs is:

Set-out convention — 305 mm in the US against 140 mm in Australia. Same trap type, 165 mm apart.
Connection method — a bolted closet flange with a gasket, covered by its own standard (ASME A112.4.3, for "the joint that connects a water closet to the sanitary drain piping"), versus a pan collar bedded in place.

Two honest qualifiers. North America is not floor-outlet-only — ASME A112.19.2/CSA B45.1 carries separate figures for bottom-outlet and for rear-outlet bowls. And the S/P split is not absolute: Caroma sells a "UNIVERSAL TRAP PAN" allowing either installation, and Roca sells dual-outlet pans. Those exist precisely because the incompatibility is real — but "normally separate products" is the accurate phrasing, not "always."

Myth 5: Product Dimensions Are Enough

Why people believe it: the fixture's own dimensions are what the factory controls, so they're what gets published.

What's true: the fixture fits the space, and the space is governed by code the supplier never reads. Worse, the two dominant US model codes disagree with each other:

Dimension	IPC 405.3.1	UPC 402.5
Centreline to side wall or obstruction	15 in (381 mm) min	15 in (381 mm) min
Centre-to-centre, adjacent fixtures	30 in (762 mm) min	30 in (762 mm) min
Clearance in front	21 in (533 mm) min	24 in (610 mm) min — 21 in only in dwelling and sleeping units
WC compartment, floor-mounted	30 × 60 in (762 × 1524 mm) min	—
WC compartment, wall-hung	30 × 56 in (762 × 1422 mm) min	—

"21 inches in front" is simply wrong on a commercial job in any UPC jurisdiction, where the requirement is 24 inches. The IPC figures come from ICC's own publication of the code text.

And accessibility inverts the logic entirely. The 2010 ADA Standards set the centreline as a range, not a minimum: "16 inches (405 mm) minimum to 18 inches (455 mm) maximum from the side wall or partition," with 60 inches of clearance from the side wall and 56 inches from the rear.

That range is the trap for anyone who assumes more clearance is always safer. An installation at 15 inches satisfies both plumbing codes and fails ADA. So does one at 24 inches. This is US federal civil-rights law, not a guideline — and the same "which figure is enforceable" problem runs through every category, which is why it pays to separate code from convention the way installation clearance dimensions does across product types generally.

What's Enforceable and What Isn't

Buyers ask "is this to standard?" and the answer depends on which kind of document you mean. Sort your spec sheet accordingly:

Legal force

IPC 405.3.1 and UPC 402.5 clearances — model codes, binding where adopted (UPC is state law in Washington)
ADA §604.2 / §604.3.1 — US federal law
UK single flush not exceeding 6 litres — statute
US 1.6 gpf federal maximum — statute

Voluntary standards — binding only when a code or contract invokes them

ASME A112.19.2/CSA B45.1 (outlet and roughing-in geometry), ASME A112.18.1/CSA B125.1 (tap-hole centres), ASME A112.4.3 (closet connector)
EN 33 (WC pan connecting dimensions) and EN 997 (WC pans with integral trap); EN 31 for wash basin connecting dimensions
EPA WaterSense at 1.28 gpf — a certification label, never a requirement
GB/T 6952 — note the T: recommended, not mandatory

Trade practice only — no legal force

The 12-inch rough-in itself, and the 10"/14" alternates
China's 305/400 mm 坑距 and their tolerance bands
Caroma's 140 mm S-trap set-out and 185 mm P-trap height
The 35 mm tap hole diameter
"Centerset" and "widespread" as words

Put the Datum on the Drawing, Not Just the Number

Every myth above reduces to the same defect: a number published without its datum, axis and outlet type. "305 mm rough-in" is unreadable in half the world's markets, because the reader cannot tell whether you measured horizontally from a finished wall or vertically from a finished floor, and to which face.

Annotation fixes this in a way a spec table cannot. Draw the dimension line on the actual product image, anchored to the actual feature it references — the outlet centreline, the finished wall face, the pan's foot level — so the datum is visible rather than assumed. Label the tolerance band next to the nominal. Mark the tap-hole centres on the deck itself instead of listing "4 inch" in a cell. A buyer reading a marked-up photograph cannot make the datum mistake; a buyer reading "305" can, and will.

This is also where measurement accuracy stops being a nicety. A callout placed by eye — or generated by an image tool that produces a plausible-looking number — is worse than no callout, because the buyer orders against it and the mismatch surfaces at installation. Measuring against the product's real edges in the image, then exporting at whatever size the buyer's catalogue or platform expects, keeps the drawing and the contract on the same number. That distinction between a stated size and a measured one is the same one that runs through nominal vs actual dimensions in every material category. If mismatched specs are already generating rejections, the return cost calculator will put a figure on what one failed container actually costs.

FAQ

What is a toilet rough-in dimension?

It is the distance from the finished wall to the centreline of the waste outlet. In the US the standard is 12 inches (305 mm), with 10-inch (254 mm) and 14-inch (356 mm) alternates sold as regular SKUs. Measure to the wall itself, not the baseboard — American Standard's guidance says "not counting the baseboard," and a baseboard can absorb 15–20 mm.

What is the difference between an S-trap and a P-trap toilet?

An S-trap discharges downward into a floor-mounted pan collar; a P-trap discharges horizontally into a wall-mounted collar. They are normally separate products rather than fittings — Caroma's Luna line ships S-trap 844710W and P-trap 844720W with different published pan dimensions (410 mm versus 395 mm). Universal and dual-outlet pans exist, but you cannot assume one.

Is the US 12-inch toilet an S-trap?

Yes. Roca markets the same vertical-outlet geometry as "S-Trap 12"" in the US and "S-Trap 305 mm" for export. This surprises suppliers who expect the US to be a separate trap type. The incompatibility between US and Australian pans is not the trap type — it is the set-out convention (305 mm versus 140 mm) and the connection method (bolted closet flange versus bedded pan collar).

What is the standard basin tap hole spacing?

Under ASME A112.18.1/CSA B125.1 there are three configurations: single hole, 102 ± 2 mm centres (the "4-inch centerset"), and 204 ± 2 mm centres (the "8-inch widespread"). The standard itself uses "centre set" and "deck fitting" and never uses the words widespread or centerset. Note that "widespread" faucets cover a manufacturer-specific range — 8–16 inches for one Kohler model, 6–12 inches for an American Standard one — so quote the dimension, not the name.

How much clearance does a toilet need?

It depends which code applies, and the two main US codes disagree. IPC requires 21 inches (533 mm) in front; UPC requires 24 inches (610 mm), relaxing to 21 inches only in dwelling and sleeping units. Both require 15 inches (381 mm) from centreline to a side obstruction. ADA is different again — a range of 16 to 18 inches to centreline, with 60 inches of clearance from the side wall — so a 15-inch install that satisfies the plumbing codes fails ADA.

What flush volume should I state for each market?

They genuinely differ, so one line cannot serve all markets. The US federal maximum is 1.6 gpf, which manufacturers print as 6.0 Lpf; WaterSense certification is 1.28 gpf (4.8 Lpf) and is a voluntary label, not a mandate. UK statute caps a single flush at 6 litres. Australian suites commonly run 4.5 L/3 L with a 3.5 L average under WELS — far below both.

Sanitaryware Specifications for Export: 5 Costly Myths