Stair Rise and Run Calculator
Compute the rise per step of a staircase given total floor-to-floor height and the number of steps, with code-compliance checks. Useful for residential stair design, deck stair planning, and remodel verification.
Last updated: May 2026
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About this calculator
Stair rise per step is the vertical height between consecutive treads, and equals total floor-to-floor height divided by the number of risers (the count of vertical step faces, which equals the number of treads plus one if there is a landing): Rise per Step = Total Rise / Number of Steps. The companion quantity, run per step (tread depth), is constrained by code and comfort and typically falls between 10 and 11 inches in residential settings. Variables: Total Rise is the finished-floor to finished-floor measurement in inches (include any subfloor and finished flooring on both levels); Number of Steps is the count of risers, normally a whole number that you adjust to keep rise per step in a code-allowed range. Code limits (2021 IRC Section R311.7 for residential): riser height maximum 7-3/4″, minimum 4″, with no more than 3/8″ variation between any two risers in a flight; tread depth minimum 10″; headroom minimum 6′-8″; minimum width 36″. Commercial stairs (IBC) are stricter: max riser 7″, min tread 11″. Comfort formulas: 2R + T = 24″–25″ (Blondel rule), R + T = 17″–17.5″, R × T = 70″–75″ — most quality residential stairs land at R = 7.5″, T = 10.5″, satisfying 2(7.5) + 10.5 = 25.5 (close to ideal). Edge cases: an odd total rise (109.5″) divided into a candidate step count produces non-integer rises that must round to within ±1/16″ across all steps; carpenters typically compute the ideal value, then adjust by adding or subtracting one step to keep rises uniform. Tread overhang (nosing) extends 0.75″–1.25″ beyond the riser face; this is separate from run depth. Open risers (no vertical face between treads) are subject to additional ball-passing rules: max 4″ sphere clearance.
How to use
Example 1 — typical residential staircase. Floor-to-floor height = 108 inches (a 9-ft ceiling with 12 inches of floor system). Aim for ~7.5″ riser. Step 1: candidate steps = 108 / 7.5 = 14.4 → round to 14 steps. Step 2: rise per step = 108 / 14 = 7.714″, which is just under the 7.75″ code maximum. Verify with comfort rule using a 10″ tread: 2 × 7.714 + 10 = 25.43″, in range. Step 3: total run = (14 − 1) × 10 = 130″ horizontal distance (13 treads between the bottom floor and the top floor). Confirm headroom: at 6′-8″ vertical clearance over the steepest point. Example 2 — deck stairs to grade. Top of deck = 48″ above ground (measured to walking surface). Aim for ~7″ riser. Step 1: candidate steps = 48 / 7 = 6.86 → round to 7 steps. Step 2: rise per step = 48 / 7 = 6.857″, well within code. Verify: 2 × 6.857 + 11 (deck stairs typically use 11″ treads) = 24.71″, comfortable. Step 3: total horizontal run = 6 × 11 = 66″ from the deck edge to the bottom step. Cross-check with the equal-rise principle: 7 risers each 6.857″ = 48.000″ total ✓. Always reverify the bottom-of-stairs ground elevation; sloped sites may require an adjusted bottom-step rise that exceeds the others, which is a code violation — re-grade or add a landing instead.
Frequently asked questions
What are the IRC and IBC code limits for stair rise and tread depth?
2021 International Residential Code (IRC) Section R311.7 sets maximum riser height at 7-3/4″ and minimum at 4″, with no more than 3/8″ variation between the tallest and shortest riser in any flight. Tread depth minimum is 10″, measured horizontally from nosing to nosing. Open risers must not allow a 4-inch-diameter sphere to pass through. Stairs over 30″ in height must have a continuous handrail 34″–38″ above the nosing line on at least one side, with a return at top and bottom. 2021 International Building Code (IBC) Section 1011 governs commercial stairs: maximum riser 7″, minimum tread 11″, with width depending on occupant load (44″ minimum for under 50 occupants, more for larger). Spiral and winder stairs have additional dimensional requirements. Always verify the current code edition adopted in your jurisdiction — local amendments are common.
How do the comfort formulas (Blondel rule and others) help design a good staircase?
Three classical formulas have guided stair design for centuries. Blondel's Law: 2 × Rise + Tread = 24″ to 25″ (originally François Blondel, 1675, based on average French stride length). Adapted formula: Rise + Tread = 17″ to 17-1/2″. Product formula: Rise × Tread = 70″ to 75″. A staircase satisfying all three is comfortable for most users. The ideal residential combination is 7″–7.5″ rise with 11″ tread, giving 2(7.25) + 11 = 25.5″, 7.25 + 11 = 18.25″, 7.25 × 11 = 79.75″ — all near optimal. Steeper staircases (riser approaching 7.75″ with tread at minimum 10″) save floor space but feel tiring on the way up and unsafe on the way down. Shallower (riser 6″, tread 12″) are gentler but take more horizontal space. Public and commercial stairs use shallower geometry by code because of higher use intensity and demographic diversity.
How do I determine the right number of steps when total rise is awkward?
Take total rise (in inches) and divide by a target riser height of 7″–7.5″ to get a candidate step count. Round to the nearest whole number, then divide actual total rise by that count to find true riser height. Verify the result falls between 6″ and 7.75″ — if it exceeds 7.75″ (code limit), increase the step count by one. If it drops below 6″ (uncomfortably shallow), reduce the step count by one. For example, total rise 106″: 106 / 7 = 15.14 → try 15 steps → 106 / 15 = 7.067″, within range; or try 14 steps → 106 / 14 = 7.571″, also in range. Choose whichever gives the better comfort match with available tread depth. The total horizontal run is (count − 1) × tread depth; if floor-plan constraints limit run, shift to fewer steps with deeper treads. If headroom is constrained, more steps with shallower rise spread out the headroom requirement.
What are common mistakes when designing or building stair rise and run?
The most common mistake is measuring total rise to the wrong reference — forgetting subfloor and finished flooring on either the top or bottom level, leading to a mis-cut bottom or top riser of 1–2″ off. Another error is variable risers: a craftsman builds 14 steps at 7.7″ each but the bottom step lands on a sloped concrete floor, creating an oddball 8.3″ first step that is a code violation and a serious trip hazard. Forgetting tread nosing (typically 1″ projection beyond the riser) makes treads feel shorter than the measured depth — codes specify minimum tread depth excludes nosing. Computing 'rise + run' for the diagonal length of the stringer instead of treating them as separate quantities is another classic error. Skipping the 2R + T = 24–25 comfort check produces stairs that pass code but feel awful to climb. Finally, neglecting headroom (6′-8″ minimum) often forces a stair redesign late in framing when the framer discovers a duct, beam, or upper landing in the way.
When should I NOT use this calculator?
Skip simple rise = total / count calculations for spiral, curved, or winder stairs — those have geometry-specific tread shape requirements (minimum tread depth at the walk line, narrower at the inside) governed by separate code sections. Do not use it for ramp design — ramps follow ADA and IBC ramp rules with maximum slope 1:12 and have different geometry. Avoid it for marine, industrial, or ship stairs that follow OSHA or maritime codes with different angle and riser limits (industrial stairs can have riser up to 9.5″ at angles up to 50°). The formula does not account for landings; if a staircase changes direction or has an intermediate landing, treat each flight separately and verify landing dimensions per code (minimum 36″ × 36″ for residential). For deck stairs with sloped ground, the bottom riser must be adjusted to floor-elevation, requiring re-grading or a concrete pad. Egress stairs in larger commercial buildings require IBC analysis well beyond a simple rise/run calculation, including refuge areas, fire ratings, and stairwell pressurization. Finally, never finalize a stair design without verifying it against the actual current code edition adopted by your building department — IRC and IBC update on a 3-year cycle and local amendments are common.