Enter either the total run length of the deck or the desired total vertical drop into the Deck Slope Calculator. This calculator assumes a common drainage slope of 1/4 inch per foot and will calculate the missing value.
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Deck Slope (Drop) Formula
The following formula calculates the total vertical drop across a deck when using a common drainage slope of 1/4 inch per foot (a typical rule of thumb; always follow local code/manufacturer requirements).
\text{Drop (in)} = \text{Length (ft)} \times 0.25\ \left(\frac{\text{in}}{\text{ft}}\right)- Where Drop is the total vertical fall (in)
- Length is the total run length of the deck (ft)
To calculate the total drop at a 1/4 in/ft slope, multiply the length of the deck (in feet) by 0.25.
How to Calculate Deck Drop?
The following example problems outline how to calculate the total drop using a 1/4 in/ft slope.
Example Problem #1:
- First, determine the total length of the deck (ft).
- The total length of the deck (ft) is given as: 51.
- Finally, calculate the total drop using the equation above:
Drop = Length * 0.25
The values given above are inserted into the equation below and the solution is calculated:
Drop = 51 * 0.25 = 12.75 in (total vertical drop)
Example Problem #2:
For this problem, the variables needed are provided below:
total length of the deck (ft) = 30
This example problem is a test of your knowledge on the subject. Use the calculator above to check your answer.
Drop = Length * 0.25 = ?
