Stair Calculator

Calculate stair dimensions per IRC building code. Get riser height, tread depth, stringer length, and angle. Sorted by comfort score for optimal stairs.

Input Format

Total Rise (floor to floor)

feet

inches

Available Run (inches, optional)

Horizontal distance available. Leave blank for best comfort.

Stair Type

Stair Width (inches)

Total Rise: 108" (9.0 ft)

Recommended Configuration

Code Issues

Steps

Riser Height

5 1/8"

5.14 in

Tread Depth

14"

14.00 in

Total Run

23.3'

280"

Warning: Stair angle below 30 degrees (too shallow)

Construction Details

Stringer Length

300 1/8"

25.0 ft

Stair Angle

21.1°

Comfortable

Comfort Score

96/100

2R+T = 24.29"

Stringer Board

2x12 x 20'

Minimum 3 stringers

All Valid Configurations (sorted by comfort)

Steps	Riser	Tread	Total Run	Angle	Comfort	Code
21Best	5 1/8"	14"	23.3'	21.1°	96	Issues
20	5 3/8"	14"	22.2'	22.1°	94	Issues
15	7 1/4"	10 5/8"	12.4'	36.0°	90	Pass
16	6 3/4"	11 1/2"	14.4'	32.1°	90	Pass
17	6 3/8"	12 1/4"	16.4'	28.8°	90	Issues
18	6"	13"	18.4'	26.0°	90	Issues
19	5 5/8"	13 5/8"	20.4'	23.8°	90	Issues
22	4 7/8"	14"	24.5'	20.2°	86	Issues
14	7 3/4"	10"	10.8'	39.7°	81	Pass
23	4 3/4"	14"	25.7'	19.3°	78	Issues

IRC Building Code Requirements

Max Riser Height

7.75"

IRC R311.7.5.1 maximum riser

Min Tread Depth

10"

IRC R311.7.5.2 minimum tread

Min Stair Width

36"

IRC R311.7.1 clear width

Min Headroom

80" (6'8")

IRC R311.7.2 minimum clearance

Riser Variation

Max 3/8"

IRC R311.7.5.1 between any two risers

Nosing

3/4" - 1 1/4"

Required for treads < 11 inches

Comfort Rule

2R + T = 24-25

Ideal riser/tread relationship

Ideal Angle

30° - 37°

Most comfortable stair angles

Handrail Height

34" - 38"

IRC R311.7.8 measured from nosing

How to Use Stair Calculator

1Enter total rise (floor to floor)
2View all valid configurations
3Check building code compliance
4Get stringer and material needs

Frequently Asked Questions

What is standard stair riser height?▾

IRC building code allows max 7.75 inch risers. Ideal riser height is 7-7.5 inches. The comfort rule is 2R + T = 24-25 inches.

How deep should stair treads be?▾

Minimum tread depth is 10 inches per IRC code. Ideal is 10-11 inches. Outdoor stairs can go up to 14 inches for a more gradual climb.

How do I calculate stringer length?▾

Stringer length = √(total rise² + total run²). For a 9-ft rise with 12-ft run: √(81 + 144) = 15 feet. Add 12 inches for cutting waste.

About Stair Calculator

Calculate stair dimensions per IRC building code. Get riser height, tread depth, stringer length, and angle. Sorted by comfort score for optimal stairs.

NexTool's Stair Calculator is completely free to use with no sign-up required. Your data is processed directly in your browser and never sent to our servers, ensuring complete privacy and instant results.