The Fall Percentage Calculator helps determine the slope or gradient of a surface by expressing the vertical change in elevation as a percentage of the horizontal run. This tool is commonly used in construction, civil engineering, landscaping, and plumbing projects to ensure surfaces drain properly or meet safety standards. A fall percentage gives a simple, clear way to express how steep or shallow a slope is, making it easier to compare and evaluate designs.
This calculator belongs to the construction and civil engineering tools category. It supports accurate decisions in grading, piping, and accessibility compliance.
formula of Fall Percentage Calculator
Fall Percentage (%) = (Vertical Fall / Horizontal Run) × 100
Where:
Fall Percentage = Slope expressed as a percent
Vertical Fall = Elevation change (drop in height)
Horizontal Run = Distance across the base of the slope
Make sure both the vertical and horizontal measurements are in the same units, such as feet or inches.
This formula helps convert basic slope information into a percentage value that’s often used in building codes and regulations, such as for ADA ramps or drainage systems.
Slope Percentage Conversion Table
| Vertical Fall (in) | Horizontal Run (ft) | Fall % |
|---|---|---|
| 1 | 4 | 2.08% |
| 2 | 10 | 1.67% |
| 3 | 12 | 2.08% |
| 4 | 20 | 1.67% |
| 6 | 24 | 2.08% |
This table gives quick insight into commonly encountered slopes in piping and surface grading. Values help determine whether your design meets practical or code-based requirements.
Example of Fall Percentage Calculator
Imagine you're designing a sloped walkway. If the elevation drops 2 feet over a 40-foot horizontal distance, then:
Fall Percentage = (Vertical Fall / Horizontal Run) × 100
Fall Percentage = (2 / 40) × 100 = 5%
This means the slope of your walkway is 5%, which may be acceptable for many outdoor paths but may exceed standards for accessibility ramps, which are often limited to around 1.67%.
Most Common FAQs
A slope of around 2% (or 1/4 inch per foot) is typical for drainage to ensure water flows away efficiently without pooling.
Multiply the fall per foot (in/ft) by 100 and divide by 12 to get a percentage. For example, 0.25 in/ft = (0.25 ÷ 12) × 100 = 2.08%.
Yes. The ADA standard for ramps is a maximum of 1:12 slope, which equals 8.33%. Knowing the fall percentage helps confirm compliance with such regulations.