How is percent slope calculated?

• A. Percent Slope = (Vertical Change / Horizontal Distance) × 100
• B. Percent Slope = (Horizontal Distance / Vertical Change) × 100
• C. Percent Slope = Vertical Change × Horizontal Distance
• D. Percent Slope = (Vertical Change / Horizontal Distance) × 1000

Answer: (D)

Percent slope shows how steep a rise is relative to its horizontal distance, expressed as a percent. To compute it, use the vertical change (rise) divided by the horizontal distance (run), then multiply by 100. So the standard formula is rise over run times 100. For example, a 3 ft rise over 20 ft of horizontal distance gives (3/20) × 100 = 15%.

If you swap the order (horizontal divided by vertical), you get the reciprocal, which isn’t the slope percent. If you multiply vertical change by horizontal distance, you obtain a quantity with area units, not a slope. If you multiply by 1000 instead of 100, you’d express per mille, not percent.