Gutter Slope Calculator Open Calculator
Australia · metric

Gutter Fall Calculator Australia

Set the fall for an Australian eaves gutter in millimetres per metre and 1:X ratios — find the fall, check one you have, or plan outlets on a long run.

Australian gutter fall finder
Live

Enter the gutter run and a fall rate — the calculator returns the total fall to build in.

Live preview — the gutter tilts to your fall
level reference drop run HIGH END LOW END →
Gutter (sloped) Water flow Level reference
Enter a run and a fall rate — the fall appears here.
Copied

This Australian gutter fall calculator is metric by default and quotes fall the way it appears on local jobs — as a 1:X ratio and mm per metre. Eaves gutters are usually fallen around 1:500 toward the rainwater head or outlet, while box and valley gutters have a stricter minimum. Roof drainage is governed by AS/NZS 3500.3; use this to plan the fall, then confirm grades, gutter sizing and overflow against the current standard.

Australian reference

Eaves gutter falls

Ratiomm per mFall over 10 mUse
1:6001.7 mm/m17 mmGentle / short
1:5002.0 mm/m20 mmCommon eaves fall
1:3003.3 mm/m33 mmLong / heavy rain
1:2504.0 mm/m40 mmFast drainage
1:2005.0 mm/m50 mmBox gutter minimum
Interactive — pick a fall ratio, drag the run
level reference fall HIGH
—
Figures are guidance only. Roof drainage in Australia must comply with AS/NZS 3500.3, the NCC and local authority requirements — confirm grades, gutter sizes and overflow provisions before installing.

Designing a box gutter or a roof gutter? See the box gutter fall calculator and the roof gutter fall calculator.

Frequently asked

Questions answered

What fall should an eaves gutter have in Australia?
Australian eaves (roof) gutters are commonly laid to a fall of around 1:500 toward the rainwater outlet, with some installers using anywhere from 1:600 to 1:300 depending on run length and rainfall. Roof drainage is covered by AS/NZS 3500.3 and the relevant manufacturer literature.
How do I calculate gutter fall in mm?
Multiply the run in metres by the fall rate. A 10 m gutter at 1:500 (2 mm/m) falls 20 mm end to end. Enter the run and a ratio above to get the fall in millimetres, plus the equivalent in mm/m, percentage and degrees.
Does AS/NZS 3500.3 set a minimum gutter fall?
AS/NZS 3500.3 sets minimum grades for roof drainage, most strictly for box and valley gutters (a minimum of 1:200). Eaves gutters should be laid to fall toward outlets; practice usually lands around 1:500. Always confirm the current standard and your local requirements.
How far can an Australian eaves gutter run before an outlet?
Keep each outlet serving a limited length — often up to around 12 m — and on long walls fall the gutter both ways from a high point to an outlet at each end. The Outlets mode plans this from your total length.
Should I allow for overflow provisions?
Yes. Australian roof drainage design includes overflow measures (such as slotted gutters or overflow outlets) so a blocked or undersized system sheds water safely away from the building. Size the fall here, then design overflow to the standard.

Need the full gutter slope toolkit?

Switch between drop, slope check, max run and downspout planning on the main calculator — with the same live diagram.

Open the main calculator