Slope / Grade Percentage
Steepness of ground or a road as a percentage.
Formula
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Example
Rise 8 m over 100 m: G = 8%
How it works
Grade percentage tells you how much a surface rises or falls for each 100 units of horizontal travel. It comes from the ratio rise/run: if the vertical change is 1 unit for every 1 unit horizontally, the grade is 100%; if the rise is half the run, the grade is 50%, and so on. Multiplying by 100 simply converts that ratio into a percentage that is easy to compare and communicate.
When to use it
Use this formula when checking the steepness of roads, ramps, driveways, rails, or terrain in surveying and construction. It is also useful for drainage and accessibility calculations, where the allowable slope matters.
Worked example, step by step
A path rises 3.5 m over a horizontal distance of 70 m. G = (rise / run) × 100 G = (3.5 / 70) × 100 G = 0.05 × 100 G = 5% The grade of the path is 5%.
Common mistakes to avoid
- Using the sloped distance instead of the horizontal run
- Forgetting to multiply the rise/run ratio by 100
- Mixing up rise and run, which gives the wrong percentage
Did You Know?
Road signs warning of a '10% grade' mean 10 m of drop for every 100 m travelled.
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