Building stairs is one of the most precise tasks in residential construction. Whether you're adding deck stairs, basement stairs, or replacing an existing staircase, getting the rise-and-run math right is critical for both safety and code compliance.
Step 1: Measure Total Rise
Measure the vertical distance from the finished floor at the bottom to the finished floor at the top. This is your total rise. Measure in at least three spots and use the largest number — floors are rarely perfectly level. Use our stair stringer calculator to convert total rise into step count and stringer layout.
Step 2: Calculate Rise Per Step
Divide total rise by the number of risers. IRC 2021 sets the maximum at 7-3/4 inches per step. Most comfortable stairs land between 7" and 7-1/2" rise. Check with our rise & run calculator to verify code compliance and comfort formula (2R + T should equal 24-25").
Step 3: Determine Run Per Step
Minimum tread depth is 10 inches per code. Standard treads (two 2x6 boards or a single 11-1/4" tread board) give you 10" to 11-1/4" of run. Deeper treads feel more comfortable but extend total run significantly.
Step 4: Lay Out and Cut Stringers
You need a framing square, stair gauges, and a 2x12 board. Mark the rise on one leg and run on the other with stair gauges. Trace down the board, then cut with a circular saw — finish corners with a jigsaw or handsaw. Most stairs need three stringers: two outside, one center. Use our stair diagram calculator to generate a printable cut template.
Step 5: Install Stringers
Attach stringers to the upper floor frame with joist hangers or a ledger board. At the bottom, stringers bear on a concrete pad or footing. Ensure the bottom riser height accounts for tread thickness — subtract one tread thickness from the first riser cut.
Step 6: Install Treads and Risers
Start from the bottom and work up. Attach treads with construction adhesive and screws (three per stringer). Risers are not always required by code for exterior stairs but are required for interior. Calculate your tread material needs before buying.
Step 7: Add Railings
Railings are required when there are four or more risers (IRC R311.7.8). Height must be 34-38" measured vertically from the stair nosing. Balusters must be spaced so a 4" sphere cannot pass through. Use our handrail & baluster calculator for exact counts and cut lengths.
Common Mistakes
- Not accounting for finished floor thickness at top and bottom
- Uneven riser heights (code allows max 3/8" variation between any two risers)
- Cutting the bottom of stringers incorrectly — remember to drop the stringer by one tread thickness
- Skipping the center stringer on stairs wider than 30"
For stairs with turns, see our landing stair calculator. Building deck stairs? The deck stair calculator handles exterior-specific requirements including footing depth and pressure-treated material.