Toilet Rough-In Guide: 10, 12 and 14 Inch Factory Specs

Rough-in is the distance from the finished wall behind the toilet to the centre of the waste outlet — the flange, for a floor-outlet pan, or the wall spigot, for a wall-outlet pan. It is called a rough-in because it is fixed during the rough plumbing stage, before the drywall goes on and long before anyone carries a toilet into the room. Everything downstream — the pan you can buy, the cistern position, the seat projection — inherits that one number.

The definition sounds simple and is still the most misread measurement in the bathroom trade. It must be measured to the finished wall: tile, backer board and waterproofing all add thickness, so a rough-in measured to stud frame lands short of the mark. And it is a centre-to-centre measurement to the outlet, not to the nearest edge of the pipe — eyeball that and you can be off by a full pipe radius.

That is why every serious spec sheet, ours included, prints the rough-in as its own line item on the dimensioned drawing. A pan drawn at one outlet position cannot be 'adjusted' onto another by optimism. The number travels from the drawing to the site, or it does not travel at all.

North American floor-outlet toilets are built around three legacy sizes, and one of them owns the market:

The 12-inch standard is why US buyers can walk into any showroom and find stock. The 10- and 14-inch sizes are the trap: they look identical in photographs, they are specified in inches in the US and they punish anyone who ordered from a photo. This is also why our drawings print metric values with inch conversions rounded — a 295 mm outlet is not a 12-inch outlet, and pretending otherwise is how returns happen.

One more trap hides in adaptations. Offset flanges exist and can shift a drain a limited amount, but they complicate venting and are a site decision, not a catalog decision. The safe rule we give every programme: spec the pan to the site's actual rough-in, do not spec the site to the pan.

Europe runs a second system entirely. Wall-hung and back-to-wall pans there do not drop into a floor flange — they drain sideways through a P-trap wall outlet, a spigot built into the wall behind the pan. The mainstream European standard is a 180 mm P-trap, and the distance that matters is vertical: from the finished floor up to the centre of the wall spigot. That outlet height is what the pan's built-in trap must land on — which is why European spec sheets talk about outlet height while American boxes talk about inches from the wall.

The two systems are not interchangeable. A P-trap pan cannot land on an S-trap floor site, and vice versa, without drainage work no importer wants to discover on installation day. This is the first question we ask any new programme: which system is the destination market built on? North America is a floor-outlet, S-trap-heritage market; Europe, the UK, Australia and the Middle East are wall-outlet P-trap markets in various dialects.

Within the wall-outlet world there are dialects too — outlet diameters and spigot standards vary by country — which is why our drawings print the outlet type and value together. A P-trap is a family, not a single size.

For a floor-outlet site, measure from the finished wall — not the skirting, not the stud — to the centre of the flange bolts. If the toilet is still installed, measure from the wall to the centre of the bolt caps holding the pan down; that is the same centreline. Write down the number in both units if you work across markets.

For a wall-outlet site, measure from the finished wall face to the centre of the spigot, and confirm the outlet diameter separately. A dial caliper or the supplier's drawing beats a tape estimate here — the spigot is the part the pan's built-in trap actually lands on.

And check the second number hiding behind the first: the fixing-hole spacing on the blueprint top view is not the rough-in. We print both because both matter — one seats the pan to the floor or frame, the other is the fixing pattern — and confusing them is the single most common pre-order mistake we see in RFQs.

Our own range is built European-first, with one deliberate American option, and the full map fits in one table because we drew it that way — the range was tooled around mainstream outlet standards rather than around novelty sizes.

Read the table two ways. If you serve European, UK, Australian or Gulf programmes, sixteen of our back-to-wall pans land on the 180 mm mainstream standard the day they arrive. If you serve North American floor-outlet sites, CA10910 is the pan drawn for that world — and it is drawn at 295 mm, its own drawing value, not a re-labelled 12-inch claim.

That 295 mm value is deliberate engineering, and it is worth explaining because it shows how a factory thinks. Vitreous china shrinks as it fires, and fired ceramics hold within standard tolerances — typically around ±2%. A floor outlet drawn at 295 mm sits safely inside a 305 mm (12-inch) site even at worst-case tolerance and with wall tile build-up behind the finished surface. The 10 mm gap is not slack; it is the buffer that lets a pan seat on the first try instead of being forced, shimmed or returned.

Every value above is a drawing value. When a project needs a specific rough-in confirmed, we send the dimensioned drawing for the exact model — outlet type, outlet centre and fixing pattern on one sheet — because that is the document the site actually works from.

Because it is the one specification that is physically expensive to be wrong about. A wrong glaze colour is a commercial problem; a wrong rough-in is a site problem — a pan that cannot seat, a wall that must be opened, a floor flange that must be moved. In project programmes, that cascades: the pan waits, the tiler waits, the handover date slips, and the container that already crossed an ocean crosses it back.

The failure pattern is consistent in our after-sales file: the buyer ordered from a photograph or from a competitor's top-view dimension, the site was measured to the skirting instead of the finished wall, or a 12-inch assumption travelled to a 10-inch legacy site. All three are invisible until installation day — which is exactly why they survive until then.

The fix costs nothing. Rough-in goes on the RFQ as a line item, the confirmation comes back as a drawing reference, and the packing list carries it again. We print the outlet type and value on every toilet drawing for precisely this reason: the number has to survive the whole journey from casting hall to flange.

Only with compromises, and never by default. The pan will stand off the wall by the difference, which leaves the cistern floating and the seal line stressed; offset flanges can recover part of the distance but they are a plumbing decision with venting implications, made by the site, not by the catalogue. Some manufacturers build dedicated 10-inch pans for exactly this legacy market — that is the honest solution where the demand is real.

For our part, we would rather say it plainly: our range does not include a 10-inch floor-outlet pan, and a 295 mm outlet is its own size, not a universal fit. Where a programme has a genuine 10-inch installed base, that is a tooling conversation — we have cast pans from custom drawings before, and the rough-in is one of the first numbers that conversation starts with.

The general principle travels beyond this one case: outlet geometry is cast into the vitreous body at the molding stage. It is the least negotiable dimension a toilet has, which is why it deserves to be the most verified one in the RFQ.

Five numbers and one document. The destination system — floor-outlet S-trap or wall-outlet P-trap. The rough-in value, measured to the finished wall at the site or taken from the project drawing. The outlet diameter, confirmed against the pan's built-in trap. The fixing pattern, read from the drawing's top view. The pan projection, which decides how far the finished toilet stands into the room. And the document: the dimensioned drawing for the exact model, with all five printed on it.

Every one of those is a 30-second check on our model pages and drawings, and every one of them is cheaper to confirm in an email than in a reopened wall. For distributor programmes, we recommend adding the rough-in line to the order confirmation itself — it turns the site conversation into a paper trail.

That is the whole discipline. Rough-in looks like a plumbing footnote; it is actually the number the entire bathroom was built around. Treat it like the spec it is, and it quietly never becomes a problem.

What is toilet rough-in? The distance from the finished wall behind the toilet to the centre of the waste outlet — the floor flange on a floor-outlet pan, or the wall spigot on a wall-outlet pan. It is fixed during rough plumbing, before walls are closed, and every downstream choice inherits it.

What is the standard rough-in in the US? 12 inches (305 mm) for floor-outlet toilets in virtually all modern construction, with 10-inch (254 mm) and 14-inch (356 mm) legacy sizes in older homes. A pan drawn for one of those sizes will not properly seat on another.

How do I measure my toilet rough-in? From the finished wall — tile included — to the centre of the flange bolt caps if a toilet is installed, or to the centre of the flange if it is not. Never measure to the skirting board or the stud frame; both make the reading short.

Is 180 mm the same as a 12-inch rough-in? No. 180 mm (about 7 inches) is the mainstream European P-trap wall-outlet standard — an outlet height measured from the finished floor to the centre of the wall spigot, a different system from the US floor-outlet inch standards. The two are not interchangeable without drainage work.

What rough-in do TAITAO toilets use? Our range is built around the European mainstream: 16 back-to-wall pans at a 180 mm P-trap wall outlet (measured as outlet height from the finished floor), 3 pans (CT10502, CT10505, CT10819) at 185 mm, the wall-hung CH10603 at a 55 mm P-trap, and the one-piece CA10910 drawn at a 295 mm S-trap floor outlet. The 295 mm is deliberate: with fired-ceramic tolerances around ±2%, it seats safely inside a 305 mm (12-inch) site with buffer to spare — including wall tile build-up.

Do you make a 10-inch rough-in toilet? Not in the current range. Where a programme has a genuine 10-inch legacy installed base, that is a custom tooling conversation — outlet geometry is cast into the body, so we would start from your site drawing.

Can I use an offset flange to fix a rough-in mismatch? It exists and sites use it, but it shifts the drain only a limited amount and adds venting complexity — it is the plumber's call on site, not a catalogue assumption. The reliable answer is to spec the pan to the measured rough-in.

Why does the fixing-hole spacing matter if it is not the rough-in? Because the pan has to be fixed as well as drained — the fixing pattern seats the pan to the floor or the carrier frame. On European-style drawings the top view often shows the fixing spacing (like 180 mm between holes) while the rough-in is printed separately; confusing the two is the most common pre-order error we see.

Where does TAITAO print the rough-in? On the dimensioned drawing of every model — outlet type, outlet centre and fixing pattern on one sheet, in millimetres with inch conversions rounded. Ask for it with any RFQ; it is the document the site will actually work from.