What the Slope Percentage Calculator Does
This tool converts a slope's two basic measurements — the rise and the run — into four useful outputs at once: slope percentage, slope as a decimal, the angle in degrees, and a simplified ratio. It is unit-agnostic, so you can enter both values in metres, feet, centimetres or inches, as long as they share the same unit. It is widely used in construction, landscaping, road and ramp design, roofing, and drainage planning anywhere in the world.
The Two Inputs You Enter
- Rise (Vertical Distance) — how much the surface goes up (or down) over the measured stretch.
- Run (Horizontal Distance) — the level, horizontal distance covered.
The Formula
The core calculation is simply:
Slope Percentage = (Rise ÷ Run) × 100
From the same two numbers the calculator also derives:
- Decimal slope = Rise ÷ Run
- Angle in degrees = arctan(Rise ÷ Run), converted to degrees
- Ratio = "1 : (Run ÷ Rise)", rounded to two decimals
Worked Example
Suppose a path climbs a rise of 2 metres over a run of 20 metres.
- Slope percentage = (2 ÷ 20) × 100 = 10%
- Decimal slope = 2 ÷ 20 = 0.1
- Angle = arctan(0.1) ≈ 5.71°
- Ratio = 1 : (20 ÷ 2) = 1:10
So a 2 m rise over 20 m is a 10% grade — a moderate but noticeable incline.
Frequently Asked Questions
Is slope percentage the same as the angle in degrees? No. A 100% slope is not 90° — it is a 45° angle, because percentage is rise over run, not the angle itself. The calculator shows both so you don't have to convert manually.
What units should I use? Any length unit works, but the rise and run must use the same unit. Because the formula is a ratio, the units cancel out and the percentage stays the same.
Why does my ratio look unusual? The ratio is always written as "1 : (run ÷ rise)". For a gentle slope this gives a large second number (e.g. 1:20); for a steep slope it gives a small one (e.g. 1:2). If the rise is larger than the run, the ratio will be less than 1:1.
