Utility Offset and Depth Table
A free, browser-based tool. Runs entirely in your browser — no sign up, nothing stored.
Utility survey points
| Chainage | Surface RL | Offset (m) | Depth (m) | |
|---|---|---|---|---|
Depth is measured from the surface down to the utility. Runs in your browser.
Invert levels
| Chainage | Surface RL | Depth | Invert RL |
|---|---|---|---|
| 0.000 | 50.000 | 1.200 | 48.800 |
| 10.000 | 49.800 | 1.350 | 48.450 |
| 20.000 | 49.600 | 1.500 | 48.100 |
Invert RL = surface RL − depth.
How to use this calculator
- For each survey point, enter the chainage, the surface RL, the offset and the measured depth to the utility.
- Add a row per point along the service.
- Read the invert RL of the utility, plus the lowest invert and deepest cover.
How it works
The invert RL is the surface RL minus the depth measured down to the utility: invert RL = surface RL − depth.
Tracking the offset and depth down a run lets you plot the service and check minimum cover.
Worked example
1.2 m cover at RL 50.0. Surface RL 50.000, depth 1.200 → invert RL 48.800. As the surface falls and depth grows, the invert keeps dropping down the run.
Frequently asked questions
Is invert the top or bottom of the pipe?
By convention the invert is the inside bottom of the pipe. If your depth was measured to the top (the obvert/crown), subtract the pipe diameter to get the invert.
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.