What is the maximum riser height allowed?

The maximum riser height allowed is 7.75 inches according to IRC guidelines.

What is the minimum tread depth required?

The minimum tread depth required is 10 inches as per IRC standards.

Is headroom included in the total rise calculation?

No, headroom is not calculated in the total rise; it must be considered separately.

Stair layout for a 42 inch rise

Calculate your stair design with a total rise of 42 inches. Adhere to IRC guidelines for riser and tread dimensions to ensure safety and compliance.

Formula SSC-2026.1

IRC check pass

Risers / treads

6 / 5

Riser inside 4 to 7.75 in

Exact riser

7 in

177.8 mm

Total run

4 ft 4 1/2 in

1,334 mm

Stringer length

5 ft 7 1/4 in

Order 8 ft 2x12

Incline

38.66°

Square 7 in rise · 10 1/2 in run

Stringers @ 16 in

Throat 5.43 in on a 2x12

Notched 2x12 side profileLive scaled blueprint

Rise, run, and the incline are scaled from the live riser and tread. Framing-square gauges match the exact riser and the tread depth.

Bill of materials and shopping list
Item	Net	Waste	Order	Unit price	Line total	Source Spec Material / Tool
8 ft 2x12	6.19 ft cut	end cuts included	3 boards	USD	$50.40	Source Spec Material / Tool
Stringer delivery weight	67 lb	—	30 kg	2.8 lb/ft planning weight	—	Source Spec Material / Tool

Source links open a product search on the Amazon storefront for the selected currency. SiteSpecCalc may earn a commission. The link does not change the quantities above.

Side-by-side target riser
Target	Risers	Exact riser	Run	Angle	Check
7 in	6	7 in	4 ft 4 1/2 in	38.7°	Pass
7 1/2 in	6	7 in	4 ft 4 1/2 in	38.7°	Pass
7 3/4 in	5	8 3/8 in	3 ft 6 in	45.0°	Warning

Show the deterministic formula

Risers = round(total rise ÷ target rise). Exact riser = total rise ÷ risers, reported to the nearest 1/16 in and in millimeters. Treads = risers − 1. Total run = treads × tread depth.

Diagonal = hypotenuse of stringer rise and total run. A dropped header uses total rise minus landing thickness. Stock is the next 8, 10, 12, 14, 16, 18, 20, or 24 ft board.

Stringers = floor(width ÷ 16) + 1, with a minimum of 2. Throat ≈ 11.25 − (riser × tread) ÷ hypotenuse.

Contractor sign-off

Project: Stair layout for a 42 inch rise

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This sheet is an estimate for ordering and layout discussion. It is not a sealed design. Confirm the quantities with a licensed local professional and the authority having jurisdiction before you buy or build.

Engineering notes

When designing stairs with a total rise of 42 inches, ensure that each riser does not exceed 7.75 inches and each tread is at least 10 inches deep, as per IRC guidelines. This will help in creating a comfortable and safe stairway.

Note that headroom is not calculated in this design, so be sure to account for it separately to meet building codes.

Code reference

IRC guidelines for stair design.

Field questions

What is the maximum riser height allowed?: The maximum riser height allowed is 7.75 inches according to IRC guidelines.
What is the minimum tread depth required?: The minimum tread depth required is 10 inches as per IRC standards.
Is headroom included in the total rise calculation?: No, headroom is not calculated in the total rise; it must be considered separately.