Cross Section Offset RL Table Builder
A free, browser-based tool. Runs entirely in your browser — no sign up, nothing stored.
Offset & reduced level
| Offset (m, − left / + right) | Reduced level (m) | |
|---|---|---|
List the points left to right (increasing offset). Offset 0 is the centreline. Runs in your browser.
Cross-falls
| Segment | Run | Rise / fall | Cross-fall | 1 : N |
|---|---|---|---|---|
| -3.000–0.000 | 3.000 | -0.100 | -3.333% | 1:30.0 |
| 0.000–3.000 | 3.000 | +0.200 | 6.667% | 1:15.0 |
Cross-fall = (RL change ÷ offset change) × 100 between adjacent points. A typical sealed-road crossfall is around 2.5–3%.
How to use this calculator
- Enter each point's offset from the centreline (negative left, positive right) and its reduced level, left to right.
- Add or remove points to match your cross section.
- Read the cross-fall of each segment as a percentage and 1:N, plus the centreline RL and section width.
How it works
Between each pair of points the cross-fall is the change in reduced level over the change in offset: cross-fall = (RL₂ − RL₁) ÷ (offset₂ − offset₁) × 100, shown as a percentage and a 1 in N ratio.
Offset 0 is the centreline, so its reduced level is shown separately. A cross section runs across the road; a long section runs along it.
Worked example
Offsets −3, 0, 3 at RL 50.1, 50.0, 50.2. The left segment falls to the centreline at −3.33%, and the right segment rises at +6.67%, with the centreline at RL 50.000.
Frequently asked questions
What's a normal road cross-fall?
A sealed carriageway is commonly around 2.5–3% from the crown to the edge, to shed water. Check the design standard for your job.
Is this official course material?
No. It is free study support mapped to surveying course levels — not official North Metropolitan TAFE content or advice. Always follow your lecturer and the official assessment brief, and check your own working.
Related tools
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.