What is a good elevation grade for drainage?

Around 2% (about 1:50) is the widely used minimum for ground or paving that needs to shed water away from a building. Flatter than that, water tends to pool rather than run off.

What angle is a 5% grade?

A 5% grade equals a rise:run ratio of 1:20 and an angle of elevation of about 2.86 degrees, found from angle = arctan(0.05).

How much does a site grade survey cost in Australia?

A surveyor callout to assess site or terrain grade for drainage, driveway, or foundation work in Australia typically costs around A$250-A$650, depending on the size of the site and how easily it can be accessed.

Elevation Grade Calculator — Slope Grade % and Angle from Rise/Run

Elevation Grade Calculator: Grade Percentage, Ratio & Angle from Rise and Run

Elevation grade — also called slope percentage — describes how much a surface rises or falls over a given horizontal distance, and it drives basic decisions on driveways, drainage runs, footpaths, and road design. This calculator takes the rise (vertical change) and run (horizontal distance) you enter and instantly returns the grade as a percentage, the equivalent rise:run ratio, and the angle of elevation in degrees, so you can check a slope against the typical minimums and maximums used for grading, drainage, and paving work.

How to use the elevation grade calculator

Enter the rise — the vertical change in height between your two points, in your chosen unit (ft/in or mm/cm/m).
Enter the run — the horizontal distance between the same two points, in a matching unit.
Read off the grade percentage, the simplified rise:run ratio, and the angle of elevation in degrees.

The elevation grade formula, explained

Grade percent = (rise / run) x 100. The angle of elevation comes from the same right triangle: angle = arctan(rise / run).

Worked example: a rise of 1 foot over a run of 20 feet gives a ratio of 1:20, a grade of (1/20) x 100 = 5%, and an angle of arctan(0.05) = 2.86 degrees.

Grade guidelines to keep in mind

Ground sloping away from a building generally needs a minimum grade of around 2% (roughly 1:50) for the first couple of metres to drain water away from the foundation — anything flatter risks pooling instead of runoff.

Road and driveway grades are usually kept well below ramp or stair slopes — many authorities treat anything above about 8-10% as steep enough to need special surfacing, guardrails, or a reduced design speed, so always check the standard that applies locally rather than assuming one fixed number.

A surveyor assessing site or terrain grade for drainage, driveway, or foundation work in Australia typically charges around A$250-A$650, depending on site size and access.