Calculate the number of risers, individual riser height, number of treads, total horizontal run and stringer length for your deck stairs. Enter the total rise (deck height above ground), tread depth and stair width — the calculator checks your design against IRC 2021 code requirements automatically.
Enter rise and tread dimensions.
The International Residential Code (IRC) sets minimum requirements for residential deck stairs that most US jurisdictions adopt:
The stringer is the diagonal board that supports the treads and risers. Its length is calculated using the Pythagorean theorem:
Stringer Length = √(Total Rise² + Total Run²)
For a deck 48 inches (4 ft) above grade with 7 treads at 11 inches each (Total Run = 77 in): Stringer = √(48² + 77²) = √(2304 + 5929) = √8233 ≈ 90.7 inches (7.56 ft). Purchase 10 ft stringers to allow for cuts and a beveled top.
Beyond code compliance, comfortable stairs follow an ergonomic formula:
2 × Riser + Tread = 24–25 inches
A 7-inch riser with an 11-inch tread: 2(7) + 11 = 25 ✓ — comfortable. A 7¾-inch riser with a 10-inch tread: 2(7.75) + 10 = 25.5 — slightly steep but still code-compliant. Aim for risers between 6.5 and 7.5 inches for the most comfortable climb.
A 36-inch rise divided by a 7-inch riser height = 5.14, rounded up to 6 risers (5 treads). Each riser would be 36 ÷ 6 = 6 inches — comfortable and well within code.
Deck stringers are typically cut from 2×12 dimensional lumber (1.5×11.25 in actual). The notched stringer must retain at least 3.5 inches of solid wood at every cut.
Yes. Most codes require footings at the base of deck stairs that extend below the frost line. A concrete pad or post footing prevents movement that could cause the stairs to pull away from the deck.