How to Lay Out Stair Stringers
To lay out stair stringers, measure the finished-floor-to-finished-landing rise, divide it into equal risers, and set the tread run to meet your plan and local code. Mark the repeated rise and run with a framing square, then adjust the top and bottom for finish materials. Dry-fit one stringer before using it as a pattern for the others.
A stair can look even at a glance and still have a code problem: under typical IRC provisions, the largest and smallest risers in a flight cannot differ by more than ⅜ inch. That is why stringer layout starts with careful measurements, not a framing square. The square repeats your numbers; it cannot correct the wrong ones.
I treat the first and last risers as the most important checks. Finished flooring, tread thickness, and the way the upper stringer connects can change their heights. Check your locally adopted code and the stair design before cutting. Local rules may differ, and some stair types have exceptions.
Inspect Stair Openings, Landings, and Supporting Framing
Before laying out a stringer, establish the exact finished elevations at both ends of the stair. Measure the opening, clear headroom, stair width, and connection points, and identify the framing or concrete that will carry the stair. These checks give your calculations a sound starting point.
- Measure finished-floor to finished-floor rise. Use a level or laser to measure vertically from the planned finished surface at the bottom to the finished landing surface at the top. Do not measure only between bare joists or subfloor if flooring will be added.
- Confirm the stair width and space available. Check the opening, landing depth, and the path for carrying and fitting stringers. Mark the intended stair edges.
- Check headroom. Typical IRC provisions call for at least 6 feet 8 inches, measured vertically from the stair nosing line to the ceiling or other obstruction. Verify the adopted code and any applicable exceptions.
- Inspect the supports. Identify where the top and bottom of each stringer will bear or connect. Confirm that the wood framing is sound and suitable for the connection. For concrete, use a designed, rated anchor system for the actual concrete and loading. Do not assume a floor-deflection rule such as L/360 proves a stair or stringer is adequate.
- List finish thicknesses. Record the thickness of the bottom floor finish, stair treads, and upper landing finish. If the exact materials are not chosen, use confirmed project specifications before cutting.
| Check before layout | What to record | Why it matters |
|---|---|---|
| Finished rise | Vertical distance between finished surfaces | Sets the total rise to divide equally |
| Tread and floor thickness | Actual or specified thickness | Affects first and last finished risers |
| Headroom | Vertical clearance above nosing line | May limit stair location or geometry |
| Support points | Bearing and connection locations | Determines top and bottom cut details |
Calculate Rise and Run, Then Mark and Cut Stringers Precisely
The unit rise is the height of each step; the unit run is the repeated horizontal distance from one step to the next. Divide the finished total rise into equal risers, then mark the run required by the stair plan. This keeps the layout consistent from the bottom to the top.
Calculate the number and height of risers
Typical IRC residential provisions limit riser height to 7¾ inches and require at least 10 inches of tread depth. They also limit the variation between the highest and lowest riser, and between the deepest and shallowest tread, to ⅜ inch within a flight. Check your local code, stair type, and plans for applicable requirements.
Choose a whole number of risers that keeps the unit rise within the allowed limit. A practical first check is to divide the total rise by 7¾ inches and round up to a whole riser count. Then divide the total rise by that count to get the equal unit rise.
Example: A finished rise of 105½ inches requires at least 14 risers under a 7¾-inch maximum. Dividing 105½ by 14 gives a unit rise of about 7.54 inches. This is a calculation example, not a complete code approval; check the rest of the stair design and local rules.
Set the run and mark the pattern
Use the tread depth required by the plan and code. Typical IRC provisions call for at least 10 inches, but confirm the measurement method and any nosing rules that apply. When using a framing square, set its stair gauges to the chosen unit rise and run. The gauges hold those dimensions while you mark each step.
- Lay a straight, sound piece of suitable structural-grade lumber on stable supports. Check it for bow, twist, large defects, and damage.
- Set one square leg to the unit rise and the other to the unit run. Keep the square firmly against the stringer edge.
- Trace the first rise and run. Slide the square so the previous line meets the next starting point, then repeat for each step.
- Count the marks. Check that the layout has the planned number of risers and the intended number of tread positions before cutting.
- Mark the top and bottom connection details from the stair plan. Do not assume a standard top cut or bottom cut fits every framing condition.
A stair with 14 risers usually has 13 intermediate treads before the upper landing, but the actual tread and landing arrangement depends on the design. Draw the full stair profile or use a project plan to confirm the count and total run before cutting.
Adjust the end risers for finish thickness
The finished first and last risers must match the other risers. Account for the bottom floor finish, tread thickness, and upper landing finish in the stringer geometry and connection detail. There is no one adjustment that fits every stair: it depends on where the stringer bears and how the treads and landings are built.
Write down the planned finished elevation of every tread surface, including the floor at the top and bottom. Then compare the first and last vertical distances to the equal unit rise. If either differs, revise the end cuts or connection detail before cutting the full set. Do not leave one riser short or tall and expect a floor covering to fix it.
Cut one stringer and dry-fit it
Cut the rise and run notches with care. Stop at each marked intersection; do not extend a saw cut past the corner. A deep overcut reduces the remaining wood, called the throat, and can create a weak point that may split under repeated use.
Dry-fit the first stringer at its actual top and bottom supports. Check that it bears as intended, that the layout matches the planned finished tread elevations, and that the end connections work. Make corrections to this first piece before tracing it onto the rest of the stock. Do not use a damaged or materially overcut stringer without qualified evaluation.
Secure Stringers, Verify Code Geometry, and Control Fall Hazards
A correctly marked stringer still needs sound support and a secure connection. Fastener type, stringer size, and spacing depend on span, loads, tread material, and the stair design. Use rated connectors and the specified fasteners or anchors, rather than choosing hardware by appearance.
Set the dry-fitted stringer in place and confirm its bearing and alignment. Attach it to verified wood framing with the connector and fastener schedule for that connection. For concrete, use an engineered or otherwise approved anchor detail suited to the concrete and loads. Add blocking or support where the plan or a qualified design requires it.
Once the first stringer is secure, use it as a template for matching pieces. Keep stringers aligned, and use the spacing specified for the stair width, tread material, and structural design. There is no universal spacing that works for every tread or span. Exterior stairs need fasteners compatible with both the treated lumber and outdoor exposure.
Before installing treads, check:
- Stringers are plumb, aligned, and firmly connected.
- Tread bearing is adequate and consistent.
- The top and bottom connections match the planned details.
- The measured finished risers and tread runs remain uniform.
- Headroom meets the adopted code.
- The tread and riser attachment follows the stair design and material instructions.
Do not use the stair until the connections and treads are secure. Keep the work area clear, and block access to an open stair during construction. An unsecured stringer or missing tread creates a fall hazard.
Finish, Inspect, and Maintain Treads, Risers, and Connections
Finishing does not correct a layout error. Before covering the stringers, verify the finished step dimensions and connection details. Then install the tread and riser materials according to their instructions and the stair design, and inspect the completed flight for movement or damage.
Measure each finished riser vertically and each tread consistently, using the same reference points throughout. Recheck the smallest and largest measurements against the locally adopted code; typical IRC provisions allow no more than ⅜ inch of variation within a flight. Confirm that nosing details and tread depth comply with the plan and applicable rules.
Inspect the connections after the treads and risers are installed. Look for loose fasteners, gaps at bearing points, split wood, or movement when the stair is used. Do not hide a structural concern under trim or flooring. If a stringer is cracked, substantially overcut, or poorly supported, stop and get a qualified assessment before use.
Common Layout Scenarios and What to Check
These examples show how measurements affect a stair layout; they are not substitutes for a site-specific design. The first illustrates equal riser math. The second shows why finish thickness must be included before cutting. In both cases, check the adopted code and connection design before building.
| Scenario | Layout check | Next step |
|---|---|---|
| Finished rise is 105½ in. | 14 equal risers yield about 7.54 in. each | Confirm tread depth, total run, headroom, and supports |
| Flooring will be added at the upper landing | Bare-framing measurements will not equal finished rise | Include the specified finish thickness in the end-riser check |
| Tread stock is thicker than first planned | The support elevation may change | Recalculate the first and last finished risers before cutting |
| A notch is cut past its corner | The stringer throat is reduced | Reject or obtain qualified evaluation; do not rely on adhesive or finish flooring |
On a stair layout, I check the full-scale pattern before cutting the matching stringers. A common field situation is a stair measured to bare subfloor, followed by a finish floor added later. The math may have been consistent, yet the first or last finished riser can end up different. The fix is to measure finished elevations and revise the layout before the cuts, not to disguise the difference afterward.
Frequently Asked Questions
These answers cover the most common decisions when marking a stair stringer. Exact requirements depend on your locally adopted code, stair type, materials, and connection design. Use the answers to guide your checks, then confirm the details against the project plans and applicable rules before cutting or installing.
How many risers do I need?
Divide the finished-floor-to-finished-floor rise by a chosen whole number of risers. Select a count that keeps every equal riser within the applicable code limit.
What is the maximum riser height?
Typical IRC residential provisions set a maximum of 7¾ inches. Check your local code and stair type.
What is the minimum tread depth?
Typical IRC provisions require at least 10 inches. Verify how your code measures tread depth and whether nosing rules apply.
How much can risers vary?
Typical IRC provisions limit the difference between the largest and smallest risers in a flight to ⅜ inch. Tread-depth variation has the same typical limit.
Do I measure from finished floor or subfloor?
Measure the total rise between finished floor surfaces. Include specified finish thicknesses when checking the end risers and stringer cuts.
How many treads are there for 14 risers?
A common straight flight has 13 intermediate treads before the upper landing. Confirm the tread and landing arrangement on your stair plan.
Can I use one stringer as a template?
Yes, after the first stringer has been dry-fitted and checked. Use suitable sound stock, and inspect every copy for matching cuts and defects.
How much headroom is required?
Typical IRC provisions require at least 6 feet 8 inches above the stair nosing line. Verify local rules and applicable exceptions.
What if I overcut a stringer notch?
A deep overcut weakens the remaining throat and may lead to splitting. Do not rely on glue or flooring to repair it; replace it or seek qualified evaluation.
Conclusion
Accurate stringers begin with the finished rise, equal risers, and a verified run. Record finish thicknesses, check the first and last risers, and dry-fit one stringer before making the rest. Secure the assembly to sound supports with rated hardware, then verify geometry and connections before anyone uses the stair.
(This article was written by one of our staff writers, David Chen. Visit our Meet the Team page.)
