Stormwater Invert Table Builder
A free, browser-based tool. Runs entirely in your browser — no sign up, nothing stored.
Start invert & pipe runs
| Pipe length (m) | Grade (%) | |
|---|---|---|
A positive grade falls downstream. Each pipe starts at the previous pipe’s downstream invert. Runs in your browser.
Invert table
| Pipe | Length | Grade | Up invert | Down invert |
|---|---|---|---|---|
| 1 | 30.000 | 1.00% | 50.000 | 49.700 |
| 2 | 40.000 | 0.50% | 49.700 | 49.500 |
Downstream invert = upstream invert − length × grade%. The fall on a run is length × grade ÷ 100.
How to use this calculator
- Enter the start (upstream) invert reduced level.
- Enter each pipe run's length and grade (%); add or remove runs as needed.
- Read the upstream and downstream invert of each run, with the total length, total fall and end invert.
How it works
Each pipe run falls by length × grade%, so the downstream invert = upstream invert − that fall. The next run starts at the previous run's downstream invert, so the table runs continuously down the line.
A positive grade falls downstream (the normal case for drainage). This is a study/QA aid — follow your authority's invert and cover requirements.
Worked example
Start invert 50.000, then 30 m @ 1% and 40 m @ 0.5%. Run 1 falls 0.300 m to 49.700; run 2 falls 0.200 m to 49.500. Total fall 0.500 m, end invert 49.500 m.
Frequently asked questions
Is grade entered as a percentage or 1:N here?
As a percentage. A 1% grade falls 1 m per 100 m; that's the same as 1:100. Convert a 1:N ratio to a percentage with 100 ÷ N.
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.