Deck Stair Calculator
Enter your total rise to get the number of risers, the actual riser height, the treads, and the total stair run.
What your result means
Risers is the number of steps; the actual riser height is the total rise split evenly across them, which must come out under code (7.75 inches IRC, often 7.5 locally). Treads is one fewer than risers, since the deck surface is the top step, and the stair run is how far the stairs project from the deck at an 11 inch tread depth.
How to use this calculator
- Measure total rise from ground to deck top.
- Use 7.5 in as ideal riser height.
- Read number of risers, actual riser height, treads, and stair run.
- Confirm riser height meets local code (max 7.75 in IRC).
- Add nosing and railings to your build plan.
The formula
Divide the total rise by your ideal riser height and round to a whole number of risers. The actual riser height is the rise split evenly across them. Treads are one fewer than risers, and the run is the treads times an 11 inch depth.
Worked example
Say your deck sits 36 inches off the ground and you want roughly 7.5 inch risers. That's 5 risers at 7.2 inches each, 4 treads, and a 44 inch stair run. Check the 7.2 against your local code, then add nosing and a railing.
Deck stair code limits (IRC)
| Item | Limit |
|---|---|
| Max riser height | 7.75 in |
| Min tread depth | 10 in |
| Riser uniformity | within 3/8 in |
| Handrail required | over 30 in tall |
| Min stair width | 36 in |
Tips & gotchas
- IRC caps riser height at 7.75 inches. Many local codes are stricter at 7.5.
- Minimum tread depth is 10 inches per IRC; 11 is more comfortable.
- Riser heights have to be uniform within 3/8 inch, or the stairs feel wrong and can fail inspection.
- Add a 1 inch nosing at the front of each tread.
- A handrail is required on any deck stair over 30 inches tall.
Frequently asked questions
How many stairs for a 36 inch tall deck?
5 risers at 7.2 inches each. Use the calculator for any height.
What's the max stair riser height?
7.75 inches per IRC, though local codes are often 7.5.
Do I need stair railings?
Yes, for any deck stair over 30 inches tall under the IRC.
How wide should deck stairs be?
36 inches minimum per IRC; 48 is more comfortable.
Should treads overhang the risers?
Yes, a 1 inch nosing is standard.
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