Toilet Suite Rough-In and Set-Out Sizes Explained (Without the Guesswork)

Choosing the right toilet suite should be simple, yet it’s one of the most common points of confusion during bathroom renovations and replacements. Terms like rough-in, set-out, S-trap and P-trap often cause uncertainty, and buying the wrong toilet can quickly lead to plumbing changes, delays, and added costs.

This guide explains toilet rough-in and toilet set-out sizes in clear, practical terms so builders and DIY renovators can choose the correct toilet suite the first time.

What toilet set-out do I need?

Your toilet set-out is the distance from the finished wall to the centre of the waste outlet. Most Australian homes fall between 140–165 mm, but older properties may differ. Measuring this accurately before purchasing a toilet suite ensures it aligns with existing plumbing and avoids costly modifications.

Toilet rough-in vs toilet set-out: what’s the difference?

Although the terms are often used interchangeably, they describe different stages of the build.

What is a toilet rough-in?

Rough-in refers to the plumbing stage where waste pipes are installed before walls and floors are finished. This is typically handled during construction and isn’t something most homeowners need to measure.

What is the toilet set-out?

Toilet set-out is the key measurement for buyers. It’s taken once the bathroom is finished and tells you whether a new toilet suite will fit your existing plumbing without moving pipes.

Why it matters

If the set-out doesn’t match the toilet’s specifications, installation becomes difficult or impossible without plumbing changes.

How to measure your existing toilet set-out

Measuring your toilet set-out only takes a few minutes:

1. Measure from the finished wall (tiles, not skirting)
2. Measure straight out to the centre of the waste outlet
3. Record the distance in millimetres

Common Australian toilet set-out sizes

While there are variations, the most common ranges include:

• 140–165 mm – typical in modern homes
• 180 mm and above – sometimes found in older bathrooms

Some toilet suites allow a small tolerance, but always compare your measurement with the manufacturer’s diagram.

Back to wall toilet vs close coupled toilet: sizing differences

Understanding toilet design helps when working with existing set-outs.

Back to wall toilets

A back to wall toilet sits flush against the wall, concealing pipework and creating a cleaner look. These toilets often allow more flexibility in set-out, making them popular for replacements where measurements aren’t perfectly standard.

Close coupled toilets

A close coupled toilet has the cistern fixed directly to the pan. They are widely used and cost-effective, but generally require closer alignment with the specified set-out.

Which is easier to replace?

Back to wall toilets are often more forgiving for replacements, while close coupled toilets work best when measurements closely match the product specifications.

Trap types explained: S-trap vs P-trap

Trap type is just as important as set-out when choosing a toilet suite.

• S-trap: waste outlet goes through the floor
• P-trap: waste outlet goes through the wall

Many toilet suites are available in both configurations, but you must select the correct one to suit your plumbing. Set-out measurements are usually discussed for S-trap toilets, so always confirm your trap type first.

Common toilet suite sizing mistakes (and how to avoid them)

These mistakes are responsible for most toilet returns and plumbing issues:

• Assuming all toilet suites are interchangeable
• Measuring from the skirting instead of the finished wall
• Ignoring trap type
• Not checking set-out tolerances
• Choosing style before confirming measurements

Avoiding these errors saves time, money and frustration.

Choosing the right toilet suite for your bathroom layout

When selecting a toilet suite, consider:

• Replacement vs renovation: replacements need closer matching
• Bathroom size: compact spaces often suit back-to-wall toilets
• Cleaning preferences: concealed pipework is easier to clean
• Budget and availability: standard set-outs are easier to source

Matching the toilet to your existing layout reduces installation complexity.

Frequently Asked Questions (FAQs)

What is a toilet set-out?

The distance from the finished wall to the centre of the waste outlet.

Can I replace a toilet without moving plumbing?

Yes, if the new toilet suite matches your existing set-out and trap type.

What toilet set-out is most common in Australia?

Most modern homes fall between 140–165 mm.

Are back to wall toilets easier to install?

They often provide more flexibility and hide pipework, making replacements easier.

What happens if the set-out is wrong?

Plumbing modifications or a different toilet suite may be required.

Choose the right toilet suite with confidence

Understanding toilet suite rough-in and toilet set-out sizes removes the guesswork from toilet replacement. Measure carefully, confirm your trap type, and choose a toilet that suits your existing layout.

Explore the full range of toilet suites designed for Australian bathrooms or speak with the team for guidance before buying.

A few careful measurements now can save significant time and cost later.