Drain Fall – free drain grade calculator

Start of the drain

Both are optional. Fill in either to get levels or laser readings at every peg.

Drain type Job or site Start invert level (RL)

Laser staff reading at start

Levels and readings are to the invert (inside bottom) of the pipe. Laser readings get bigger as the drain goes down.

Drain legs

One row for each straight length between bends, junctions or pits, in order from the top end.

Usual minimum grades

Pipe	Minimum grade	Fall per 10 m

Sanitary drains, from AS/NZS 3500.2. Some fixtures, authorities and site conditions need more. Stormwater grades are set by AS/NZS 3500.3, the plans and the local council.

Long section

Peg levels

Every

A guide only. Check levels on site, the approved plans, the sewer connection depth and AS/NZS 3500. Grades are kept to the nearest millimetre, so measure from the start each time rather than adding up small steps.

The two ends

For example the house drain outlet and the sewer connection point (junction or inspection opening).

I have Top end (start)

Bottom end (connection)

Length of the run

Pipe Drain type

Use the length along the pipe route, including bends, not the straight-line distance.

Result

A guide only. Check levels on site, the approved plans and AS/NZS 3500. Allow for the depth of cover the pipe needs along the way.