Pipe & laser grade calculator
Work out the fall over a run, the grade between two inverts, a set-out table for your string line, and the combined grade when you dial two axes into a grade laser.
Fall over a run
Enter the grade as a percent or as 1 in X, then the length of the run.
Set-out table
Fall at each chainage along the run, using the grade and length above.
| Chainage | Fall from start | Invert RL |
|---|
Grade from two inverts
The invert levels at each end and the length between them.
Dual-axis laser: combined grade
Dial X and Y grades into a dual-grade laser and this is the true slope of the plane and the direction it falls.
Minimum grades for house drains
Sanitary drains under AS/NZS 3500.2, as quoted in industry guides. Sewer mains are different — your water authority sets those, and they change with how many properties connect.
| Pipe | Min grade | Ratio | mm/m |
|---|---|---|---|
| DN65 | 2.50% | 1 in 40 | 25.0 |
| DN80 | 1.65% | 1 in 60 | 16.5 |
| DN100 | 1.65% | 1 in 60 | 16.5 |
| DN150 | 1.00% | 1 in 100 | 10.0 |
Always check the current edition of AS/NZS 3500.2 and your local plumbing rules before you dig.
Setting out a grade?
Hire a grade laser or pipe laser and get it right first time.