Deck Stair Calculator
Calculate deck stair dimensions including risers, treads, stringers, and materials. Ensures code-compliant, comfortable stairs.
Vertical distance from ground to deck surface
How to Use This Calculator
Building safe, code-compliant deck stairs starts with accurate calculations. Here's how to get the dimensions right:
- Measure the total rise: the vertical distance from the ground to the top of the deck surface.
- Enter the desired stair width. Standard is 36 inches minimum; wider is more comfortable.
- Select stringer spacing based on tread material. 16 inches is standard for 2× lumber treads.
- Click 'Calculate' to get the number of steps, riser height, tread depth, and stringer dimensions.
- Verify the results meet your local building codes before construction.
Why This Matters
Improperly designed stairs are a leading cause of falls and injuries. Building codes specify strict requirements for riser height (max 7.75") and tread depth (min 10") because inconsistent stairs are dangerous. All risers must be within 3/8" of each other in height.
- Calculate code-compliant riser and tread dimensions
- Determine the exact number of steps needed
- Know stringer length and cutting angles
- Ensure comfortable, safe stairs with the 7-11 rule
- Calculate materials: stringers, treads, and riser boards
Worked Examples
Standard Deck Height
A deck 28 inches above ground with 36-inch wide stairs.
Calculation: 28" ÷ 4 steps = 7" risers. Treads: 25" - (2×7") = 11". Total run: 11" × 3 = 33".
Result: 4 risers at 7", 3 treads at 11" deep, 3 stringers (2×12×4' minimum).
High Deck
A deck 56 inches above ground.
Calculation: 56" ÷ 8 steps = 7" risers. Treads: 11". Total run: 77". Stringer: ~95" (8 feet).
Result: 8 risers, 7 treads, stringers from 2×12×10' boards. Consider a landing for stairs over 7 feet.
Low Step
A single step down from a low deck, 14 inches total rise.
Calculation: 14" ÷ 2 steps = 7" risers. One tread at 11".
Result: 2 risers at 7", 1 tread. Consider 3 stringers even for a single step for stability.
Common Mistakes to Avoid
- Measuring to the wrong point - measure total rise from finished ground to top of deck surface, not deck frame.
- Forgetting the bottom riser - the ground is your first tread, so you have one more riser than tread.
- Inconsistent risers - all risers must be within 3/8" of each other. Even small variations cause trips.
- Not accounting for tread overhang - treads typically overhang risers by 3/4" to 1-1/4".
- Using undersized stringers - after notching, at least 3.5" of wood must remain for strength.