A Deck Stringer Calculator helps homeowners, builders, and contractors determine the exact measurements for constructing deck stairs. This tool ensures that staircases are safe, functional, and meet building code requirements. Properly designed stringers provide support for the steps, ensuring stability and durability.
By using a Deck Stringer Calculator, users can determine the number of risers, total run, stringer length, and spacing between stringers. This helps prevent miscalculations that can lead to unstable stairs, excessive step heights, or uneven spacing.
Formula for Deck Stringer Calculation
To calculate the dimensions of a deck stringer, the following formulas are used:
Total Rise (R) = Deck Height – Ground Level
Where:
Deck Height = Vertical distance from the ground to the deck surface (inches)
Ground Level = Starting point of the stairs (inches)
Number of Risers (N) = Total Rise / Riser Height
Where:
Riser Height = Typically 7 to 7.5 inches (per building code)
Total Run (T) = Tread Depth × (N – 1)
Where:
Tread Depth = Recommended 10 to 11 inches
(N – 1) accounts for the number of steps needed
Stringer Length (L) = √(Total Rise² + Total Run²)
Using the Pythagorean theorem to determine the stringer’s diagonal length
Number of Stringers = (Stair Width / Spacing) + 1
Where:
Spacing = Typically 16 inches for standard wood stairs
These formulas ensure that the deck stairs are properly measured and built to meet safety standards.
Deck Stringer Reference Table
The following table provides estimated calculations for common stair dimensions, helping users quickly assess their stringer requirements.
| Deck Height (in) | Riser Height (in) | Number of Risers | Tread Depth (in) | Total Run (in) | Stringer Length (in) |
|---|---|---|---|---|---|
| 28 | 7 | 4 | 10 | 30 | 42.05 |
| 35 | 7 | 5 | 10 | 40 | 53.85 |
| 42 | 7 | 6 | 10 | 50 | 66.19 |
| 49 | 7 | 7 | 10 | 60 | 79.06 |
| 56 | 7 | 8 | 10 | 70 | 92.46 |
This table helps builders determine the correct number of risers, total run, and stringer length based on different deck heights.
Example Calculation
A homeowner is building a staircase for a deck that is 35 inches high.
Deck Height = 35 inches
Riser Height = 7 inches
Number of Risers = 35 / 7 = 5
Tread Depth = 10 inches
Total Run = 10 × (5 – 1) = 40 inches
Stringer Length = √(35² + 40²) = √(1225 + 1600) = √2825 = 53.85 inches
This means the deck requires 5 risers, a total run of 40 inches, and stringers measuring approximately 53.85 inches.
Most Common FAQs
The standard riser height is between 7 and 7.5 inches, which ensures comfortable and safe stair climbing.
The number of stringers depends on the stair width. Typically, spacing of 16 inches between stringers is used, with at least three stringers required for most decks.
The theorem calculates the hypotenuse of the stair triangle, ensuring the correct diagonal length of the stringer for proper fitting and alignment.