Calculator Inputs
Example Data Table
This sample uses a 24 m run, 1.20% slope, and 300 mm pipe diameter.
| Item | Sample Value | Unit |
|---|---|---|
| Upstream Cover Level | 102.400 | m |
| Upstream Invert Level | 100.850 | m |
| Pipe Length | 24.000 | m |
| Slope | 1.200 | % |
| Calculated Fall | 0.288 | m |
| Calculated Downstream Invert | 100.562 | m |
| Downstream Cover Level | 102.050 | m |
| Gradient Ratio | 1:83.33 | ratio |
| Upstream Crown Level | 101.150 | m |
| Downstream Crown Level | 100.862 | m |
| Upstream Depth to Invert | 1.550 | m |
| Downstream Depth to Invert | 1.488 | m |
| Upstream Cover Depth Above Crown | 1.250 | m |
| Downstream Cover Depth Above Crown | 1.188 | m |
Formula Used
Fall = Pipe Length × (Slope ÷ 100)
Downstream Invert = Upstream Invert − Fall
Upstream Invert = Downstream Invert + Fall
Slope (%) = (Fall ÷ Pipe Length) × 100
Gradient Ratio = 1 : (Pipe Length ÷ Fall)
Crown Level = Invert Level + Pipe Diameter
Depth to Invert = Cover Level − Invert Level
Cover Depth = Cover Level − Crown Level
Unit guidance
Keep all levels and lengths in metres. Enter pipe diameter in millimetres. The calculator converts diameter to metres before crown and cover depth checks.
How to Use This Calculator
- Select the solving mode that matches the unknown value.
- Enter the known levels, pipe length, and slope.
- Add cover levels if you also want trench depth checks.
- Enter pipe diameter to calculate crown levels and cover depth above crown.
- Click Calculate to show results above the form.
- Review the summary cards, full results table, and line profile graph.
- Export the results or example table as CSV or PDF when needed.
Why Sewer Invert Levels Matter
Sewer invert levels control drainage direction, self-cleansing velocity, manhole connections, and cover depth. A small level error can change slope, affect excavation depth, and create backfall issues. This page helps compare known survey levels with design assumptions before final site setting out.
FAQs
1) What is a sewer invert level?
The sewer invert level is the elevation at the inside bottom of the pipe. It is the reference used for gravity flow design and pipe setting out.
2) What is the difference between cover level and invert level?
Cover level is the surface or manhole top elevation. Invert level is the internal pipe bottom elevation. The difference between them gives the depth to invert.
3) Why is slope important in sewer design?
Slope controls how quickly wastewater flows. Too little fall can cause sediment build-up. Too much fall can create high velocities and maintenance issues.
4) What does the gradient ratio 1:N mean?
A ratio like 1:80 means the pipe falls 1 unit vertically for every 80 horizontal units. Smaller N values represent steeper grades.
5) Why enter pipe diameter?
Diameter lets the calculator estimate crown levels and cover depth above the pipe crown. That helps check burial depth and trench cover quickly.
6) Can this calculator detect reverse falls?
Yes. If the fall becomes negative, a warning appears. That usually means the assumed upstream to downstream flow direction does not match the entered levels.
7) Does trench depth equal cover depth?
No. Depth to invert measures from cover level to pipe invert. Cover depth measures from cover level to pipe crown. They are related but different checks.
8) Can this replace surveyed site levels?
No. It is a planning and checking tool. Final design and construction setting out should always use verified survey control and project standards.