1, 2- or 3-bedroom granny flat: size, cost and return compared

All 3 fit inside the same legal limit. A NSW granny flat is capped at 60 m² of floor area, so a 3 bedroom is not a bigger building than a 2 bedroom, it is the same building with the space divided differently. That single fact drives every trade-off below.

Two bedroom is the most common choice in Sydney because it suits the widest range of tenants without cutting the living space to nothing.

A granny flat has one kitchen, one bathroom and one set of service connections regardless of size. Those are the expensive parts, and they cost the same at 40 m² as they do at 60 m².

Spread across 40 m², those fixed costs land heavily on every square metre. Spread across 60 m², they land more lightly. So the studio has the lowest total price and the highest rate per square metre, and the difference between a 45 m² and a 60 m² build is often smaller than people expect, because the extra 15 m² is only floor, walls and roof.

The practical consequence: if your block allows 60 m² and your budget stretches, building smaller rarely saves as much as it costs you in usable space and rental appeal.

The most space per person. With only one bedroom to fit, the living area and kitchen can be properly sized rather than squeezed.

Works well for an elderly parent who wants their own front door, an adult child, a home office with a bathroom, or a single tenant. Where it struggles is resale and rental flexibility, because the tenant pool is narrower.

The default for a reason. At 50 m² to 60 m² you can fit 2 real bedrooms, a bathroom, a kitchen and a living space that people will actually sit in.

It suits couples, a small family, 2 people sharing, or a parent with a child. That breadth is why it tends to hold rental appeal best across changing circumstances.

Three bedrooms inside 60 m² means every room gives something up. Bedrooms get smaller, the living area shrinks, and storage becomes a real design problem.

It is the right answer when the specific need is bedrooms, most often a larger family living together where the alternative is a much bigger and more expensive move. It is usually the wrong answer if the goal is rental yield, because the higher rent rarely offsets the reduced liveability and the narrower tenant appeal.

Roughly how the space divides:

The bathroom and kitchen cannot shrink much, because they have fixed minimum dimensions and fixed fittings. So every extra bedroom comes almost entirely out of the living area.

Work backwards from who is going to live in it.

• A family member for the long term. Build for their actual needs, not resale. One bedroom with a proper living space is often kinder than 2 cramped ones.
• Rental, and you want the widest tenant pool. Two bedroom.
• Rental, and you want the lowest entry cost. One bedroom or studio, accepting the narrower pool.
• A larger family under one roof. Three bedroom, going in with clear eyes about how tight 60 m² is across 3 rooms.
• You are not sure yet. Two bedroom, because it suits the most situations and is the easiest to re-let or repurpose.

Be careful with return figures you see quoted online. Rent for a granny flat depends on the suburb, the finish, the parking, the privacy from the main house, and the current rental market. A yield calculated on someone else’s block in another suburb tells you very little about yours.

The reliable way to estimate it is to look at what comparable granny flats and small units are actually renting for in your suburb right now, then work from that number rather than a generic percentage.