Stair Calculator

Calculate stair rise & run, stringer length, treads, risers, angle & costs with interactive diagrams.

Stair Rise & Run Calculator

Calculate the number of steps, riser height and tread depth for code-compliant stairs.

TOTAL RISE TOTAL RUN RISER TREAD STRINGER θ

Stair Rise & Run Results

CODE (IRC R311.7): Max riser: 7¾". Min tread: 10". Min width: 36" (above handrail). Max riser variation: ⅜". Nosing: ¾" to 1¼" projection. Headroom: min 6'8" (80"). Handrail: 34"–38" height.

Stair Stringer Calculator

Calculate stringer length, angle, and cut dimensions for wood or steel stairs.

Stringer Results

STRINGERS: Use 2×12 for most stairs. Notch depth must not exceed 50% of board width. Min 3.5" of wood remaining after notch. For stairs wider than 36", add a center (4th) stringer. Use metal stringer brackets for attachment to rim joist.

Stair Materials Calculator

Calculate all materials: treads, risers, posts, handrails, balusters and hardware.

Materials List

FASTENERS: Use 3" exterior screws (deck screws) for treads — 4-6 per tread. Use structural screws or carriage bolts for stringer connections. Pre-drill hardwood to prevent splitting. Use galvanized/SS hardware for outdoor stairs.

Stair Cost Calculator

Estimate total stair construction costs including materials and labor.

Stair Cost Estimate

BUDGET TIP: Pressure-treated pine is 40-60% cheaper than cedar or composite. Pre-cut stair stringers ($15-$30 each) save hours of layout work. Interior stairs with carpet runner cost less than hardwood treads. Always check if a building permit is required.

Stair Code Reference Guide

Building code requirements, standard dimensions and design guidelines.

IRC Building Code Requirements

Requirement IRC Code (Residential) Commercial (IBC)
Maximum Riser Height 7¾" (197 mm) 7" (178 mm)
Minimum Tread Depth 10" (254 mm) 11" (279 mm)
Minimum Width 36" (914 mm) 44" (1118 mm)
Minimum Headroom 6'8" (2032 mm) 6'8" (2032 mm)
Max Riser Variation ⅜" (9.5 mm) ⅜" (9.5 mm)
Handrail Height 34"–38" 34"–38"
Guard Height 36" min 42" min
Baluster Spacing Max 4" gap Max 4" gap
Nosing Projection ¾"–1¼" ¾"–1¼"
Landing Size ≥ stair width ≥ stair width

Comfortable Stair Ratios

Rule Formula Example Notes
7/11 Rule 7" rise, 11" run 7" + 11" = 18" Most common residential
Blondel Formula 2R + T = 24"–25" 2(7.5) + 10 = 25" French standard, very comfortable
Rise + Run R + T = 17"–18" 7 + 11 = 18" Quick check formula
R × T R × T = 70–75 7 × 10.5 = 73.5 Product rule

Stair Angle by Use

Use Angle Rise/Run Comfort
Ramp 0°–20° varies Easy access
Exterior / Deck 25°–35° 6"/12" – 7"/10" Very comfortable
Interior (standard) 30°–37° 7"/11" – 7.5"/10" Comfortable
Steep residential 38°–45° 8"/9" – 9"/9" Marginal
Ship ladder 50°–70° steep Emergency only

Stair Calculator with Diagram

Our stair calculator helps you design code-compliant stairs by calculating the exact rise and run, number of steps, stringer length, and stair angle. Enter your total floor-to-floor height and get an instant layout with all dimensions.

How to Calculate Stair Rise and Run

To calculate stair rise and run: Measure total rise (floor to floor) in inches. Divide by ideal riser height (7"–7.75") to get number of steps. Individual riser = total rise ÷ number of steps. Standard tread depth is 10"–11". For a 9-foot (108") floor-to-floor height: 108 ÷ 7.5 = 14 risers at 7.71" each, with 13 treads at 10.5" = 136.5" total run (11.4 feet).

How to Calculate Stair Stringers

The stair stringer length is the hypotenuse: √(Total Rise² + Total Run²). For our example: √(108² + 136.5²) = √(11664 + 18632) = 174 inches (14.5 feet). Use 2×12 lumber — the notch should leave at least 3.5" of wood. For stairs wider than 36", add a center stringer. Standard spacing: 3 stringers for 36", 4 for 48".

Deck Stair Calculator

For deck stairs, measure from the deck surface to the ground. A 48" high deck needs about 7 steps (48 ÷ 7 = 6.86 risers). Use pressure-treated 2×12 stringers and 2×6 or 5/4×6 treads. Set the bottom on a concrete pad or gravel footing. Deck stair costs run $15-$25 per step for materials.

Frequently Asked Questions

What is the standard stair rise and run?+
The IRC building code allows a maximum riser of 7¾" and minimum tread of 10". The most comfortable ratio is the 7/11 rule: 7" riser with 11" tread. The Blondel formula (2R + T = 24"–25") is the gold standard for comfort. Most residential stairs use 7"–7.5" risers with 10"–11" treads.
How long should stair stringers be?+
Stringer length = √(rise² + run²). For a standard 9ft floor (108" rise, ~136" run): √(108² + 136²) = ~174" (14.5 ft). Buy 16-foot 2×12 boards. For a 48" deck: √(48² + 60²) = ~77" (6.5 ft). Always add 6-12 inches for trimming. Three stringers minimum for 36" wide stairs.
How many steps for a specific height?+
Quick formula: Height (inches) ÷ 7.5 = number of risers. 36" deck = 5 steps. 48" deck = 7 steps. 9ft floor (108") = 14-15 steps. 10ft floor = 16-17 steps. Always recalculate exact riser height after choosing number of steps to ensure even spacing.
How to calculate stair angle?+
Stair angle = arctan(Total Rise ÷ Total Run). Comfortable stairs: 30°–37°. Example: 108" rise, 136" run = arctan(108/136) = 38.4°. If angle exceeds 42°, consider adding a landing to break the run. Below 30° feels like a ramp; above 42° feels too steep.