How steep is my block?
Enter your address and we will read the fall of your block off the national elevation model, then say in plain English what that slope means for building on it. You get the slope as a percentage, as a ratio, and as a fall in metres, which is how builders and the NSW Pattern Book talk about it.
NSW addresses only.
Manual slope calculator
Type the height difference between two points and the horizontal distance between them. Fill in one row or both.
Front to back
Across the site
How to measure it
On a survey, read the levels at two points along the same boundary and take the difference. On the block, a builder’s laser level or a long level line and a tape will do: hold the line level from the higher point, and measure how far it sits above the ground at the lower point.
The distance is the horizontal length between the two points, measured on the plan or with a tape held level, not the length along the slope.
What slope means
Slope is the change in level divided by the length it happens over. A block that falls 2 metres over 40 metres has a slope of 1 in 20, which is 5 percent, or a little under 3 degrees. Builders usually quote it as a percentage or a ratio, engineers sometimes in degrees, and the NSW Pattern Book publishes its limits as a fall in metres. This page shows all of them.
How this page measures it
The ground levels come from Geoscience Australia’s 5 metre LiDAR elevation model, the same data that draws the contours on our block diagrams. We measure four runs: down the left and right boundaries from the street to the back, and across the front and the rear of the site. Each run is a best fit line through every elevation cell inside that strip of the block, not a difference between two corner points, so one noisy cell cannot swing the answer. A block is often level down one side and falling down the other, so we report both sides of each direction and lead with the steeper.
It is indicative, not a survey. The model reads the ground as it was flown and cannot see a retaining wall built last year, and its cells are a few metres across. Use it to know what you are dealing with, then get a survey before you design or price anything.
What the number means for a build
| Slope | Grade | What to expect |
|---|---|---|
| under 5% | Gentle | Slab on ground is usually straightforward at this gradient. What a builder prices against is the fall in metres rather than the percentage, and most allow about 300 mm of fall across the building envelope in a standard slab, so check the fall figure against what your quote covers. |
| 5% to under 10% | Moderate | Expect cut and fill, a stepped slab or a drop edge beam, and some retaining. Drop edge beams are commonly used while the fall across the house footprint stays under about 1.2 m, so the fall figure matters more here than the percentage. |
| 10% to under 20% | Steep | Expect split level design or a raised floor rather than a single slab, engineered retaining and site costs that are a real line in the budget. In NSW a retaining wall over 600 mm has to be certified by an engineer, and many councils ask for a geotechnical report on land this steep. |
| 20% and over | Very steep | Expect pole or suspended floor construction, engineered retaining and a geotechnical report before anything is designed. Get a survey early, and treat any site cost allowance in a standard building quote as a starting point rather than a price. |
Site costs are where display village pricing meets your slope. A steep fall across the building platform adds retaining walls, drops and step downs that a flat block never pays for, so knowing the number before you sign anything is worth a few minutes.
Slope and the NSW Pattern Book
Each low rise design in the NSW Housing Pattern Book publishes how much fall it can take, front to back and across the site, as a number of metres. Our block search screens the same reading you see here against those limits, so a block that is too steep for a design is ruled out before you fall for it.
Once you know how steep the block is, the next question is which way it faces. The block direction tool answers that, and the plan search shows only homes whose living areas land on the sunny side of your block.
Browse north facing house plans