Enter the horizontal distance or the vertical height into the calculator to determine the other dimension and the slope length for a 1:20 slope.

1:20 Slope Formula

The following formulas are used to calculate the dimensions of a 1:20 slope. 

VH = HD / 20
HD = VH * 20
SL = √(HD^2 + VH^2)

Variables:

  • VH is the vertical height (units)
  • HD is the horizontal distance (units)
  • SL is the slope length (units)

To calculate the vertical height, divide the horizontal distance by 20. To calculate the horizontal distance, multiply the vertical height by 20. To find the slope length, use the Pythagorean theorem with the horizontal distance and the vertical height.

What is a 1:20 Slope?

A 1:20 slope is a gradient or incline of a surface where for every 20 units of horizontal distance, there is a 1 unit change in vertical height. This type of slope is often used in construction, landscaping, and civil engineering to ensure proper drainage, accessibility, and to meet building regulations. It is considered a gentle slope that is typically easy to walk up and is wheelchair accessible.

How to Calculate a 1:20 Slope?

The following steps outline how to calculate the dimensions of a 1:20 slope.

  1. First, determine either the horizontal distance (HD) or the vertical height (VH) of the slope.
  2. Use the formulas VH = HD / 20 or HD = VH * 20 to calculate the missing dimension.
  3. Next, calculate the slope length (SL) using the Pythagorean theorem: SL = √(HD^2 + VH^2).
  4. Finally, check your calculations with the 1:20 Slope Calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

horizontal distance (HD) = 100 units

Using the formula VH = HD / 20, the vertical height (VH) would be 100 / 20 = 5 units.

Using the Pythagorean theorem, the slope length (SL) would be √(100^2 + 5^2) = √(10000 + 25) = √10025 ≈ 100.12 units.