Stairs are one of the most regulated parts of a building, and they are also the hardest place to use a tape measure. Scanning makes it easier: just walk up the stairs once, and you can get the total rise, run, width, and headroom from the model. However, scanning cannot check if all the risers are the same height, since the code requires more precision than a phone can provide. For that, you still need to use a tape measure.
What You Need to Capture, and How
Why Measuring Stairs by Hand Is the Risky Part
When you measure a staircase with a tape, you often have to stand in the middle of the stairs, use both hands, reach over the side, or lean into the stairwell to check headroom. During renovations, you might be on loose steps, and the handrail is usually missing. You also need to repeat this for every step, since each riser must be checked.
Scanning makes the process easier. You walk up the stairs once at a normal pace while holding your device, and the model provides the measurements later. There is still some risk since you are on the stairs, but you only need to walk them once instead of spending twenty minutes with both hands occupied.
How do you scan a staircase properly?
Stairwells are among the hardest indoor spaces to scan accurately. They are narrow, enclosed, and each step looks similar, so scanners have more trouble tracking their position than in open rooms. The tips below can help with this problem.
Start at the bottom and walk up the stairs in one continuous pass. Begin on the lower landing, scan the entire flight without stopping, and finish on the upper landing. If you stop and restart, the scanner may lose its place because the stairs look so similar.
Walk about half as fast as you would in an open room. The scanner has less to track in a stairwell, and if it loses track, you could end up with a flight that looks bent or a landing at the wrong height. These mistakes may not be obvious until you review the measurements.
Be sure to scan both landings carefully, as they connect the stairs to the floors above and below. If you miss them, the stairs will not be anchored in the model, and the total rise measurement will not be reliable. All other measurements depend on getting the total rise correct.
Capture both the ceiling line and the steps. Headroom depends on the space between the nosings and anything above them, so if you scan the stairs but miss the soffit or joists, you will not get a proper clearance profile.
Scan the underside of the stairs where they connect to the structure. This area includes the stringers, carriage, and the space below the flight, which are often changed during renovations.
What should you verify before leaving?
- Check these steps in order, as each one helps you catch a different type of mistake.
- Look at the mesh preview for any holes or a flight that appears bent.
- Use a tape or laser distance meter to measure the total rise from floor to floor. This measurement sets your scale and is the basis for counting risers.
- Measure one riser and one tread at both the top and bottom of the stairs. These areas are where finish thickness can change and where uniformity problems are most likely.
- If you need to check for code compliance, measure every riser. The 3/8-inch rule applies to the entire flight, so measuring just a sample is not enough.
For more information on measuring buildings as a whole, see How to Measure a Building Without a Total Station.
The Numbers a Stair Has to Hit
What are the code dimensions for stairs?
Most US residential work follows the IRC. In the 2024 edition, the limits are a maximum riser height of 7 3/4 inches, measured vertically between the leading edges of adjacent treads, and a minimum tread depth of 10 inches, measured horizontally between the foremost projections of adjacent treads at a right angle to the leading edge. The figures throughout this section are from that edition.
Stairs must be at least 36 inches in clear width, and headroom at least 6 feet 8 inches, taken from the sloped line running along the tread nosings rather than from any individual tread. A single flight cannot rise more than 12 feet 7 inches between floor levels or landings.
One detail is more important for measurement than it might seem: the 3/8 inch uniformity limit applies to riser heights, tread depths, and how far nosings project across a flight. This is the strictest number you will need to confirm on a stair.
Commercial work under the IBC is tighter, with risers capped at 7 inches and treads at a minimum of 11 inches.
Before you rely on these numbers, keep in mind that two things can change them.
States and municipalities often change the model code, sometimes by a lot. The only numbers that matter are those from the jurisdiction issuing your permit, so always confirm with the local building department before starting work.
Also, all these measurements are taken between finished surfaces. The code does not include carpets, rugs, or runners. A stair that meets code before flooring is installed might not comply after the finish is added.
Why does the 3/8 inch rule matter?
People often focus on individual measurements, but the uniformity rule is what really determines if a staircase is safe to use.
Within a single flight, no riser can be more than 3/8 inch taller than the shortest one, and tread depths follow the same rule. This is for safety, not just for code. When you climb stairs, your body gets used to the step height and you stop looking at your feet. If one riser is different, it can cause a trip, which is why the code focuses on consistency across the whole flight, not just the tallest step.
Matching the Tool to the Tolerance
Polycam Space mode for LiDAR devices is accurate to within half an inch on standard interiors. The code allows only 3/8 inch of variation across a flight, which is stricter than the scanner's specification. Some scans may be more accurate, but the published tolerance covers different capture qualities and surface conditions, not just the best case.
To verify a tolerance, your measurement needs to be much more precise than the tolerance itself, usually by a factor of four or more. For a 3/8-inch limit, this means uncertainty should be less than a tenth of an inch. No phone-based scan can achieve this, and neither can a tape measure if you are balancing on a stair tread.
Scanning works well for large-scale measurements, like total rise from floor to floor, total run, clear width, headroom, stairwell and landing geometry, and how the stairs fit with the rest of the building. A half-inch error is minor when measuring a 108-inch rise, but it is a big problem on a 7-inch riser.
So the approach is simple: scan the flight for overall geometry, then use a tape measure to check individual risers and treads when you need to confirm compliance. This verification only takes a few minutes, and you are just checking numbers instead of figuring them out from scratch.
How do you check stair headroom?
Headroom is the dimension this workflow handles best, and it is also the one people measure least reliably by hand.
The code minimum is 6 feet 8 inches, measured vertically from the tread nosing line rather than from the floor. Checking that by hand means standing mid-flight with a tape held overhead, taking a reading at an angle, and repeating it along the run because headroom is not constant. It is exactly the posture that makes hand-measuring a stair risky in the first place.
A scan gives you the full vertical clearance profile in one walk-through. Later, you can measure at every nosing from your desk and find the tightest spot, instead of hoping you measured it on site. The error is also small: half an inch on an 80-inch dimension is less than one percent, but the same error on a seven-inch riser is over seven percent.
The tight spot is usually where a floor joist or a bulkhead crosses the flight near the top, and it is easy to miss with spot measurements taken every few steps.
How do you measure a winder stair?
On a straight flight, you can measure tread depth anywhere across the tread. On a winder, it is measured along the walkline, which the code defines exactly. The walkline curves with the turn, sits 12 inches in from the inside edge, and those 12 inches are measured from the widest part of the clear stair width at walking level. Depth changes as you move across the tread, so following that curve with a tape while standing on a narrowing step is so tricky that two people rarely get the same result.
For that reason, the code treats winders separately. A winder tread needs at least 10 inches of depth where the walkline crosses it, and at least 6 inches anywhere within the clear width. The 3/8 inch uniformity limit applies at the walkline, though consistently shaped winders may share a flight with rectangular treads without matching their depth.
A scan captures the whole geometry at once, so the walkline can be constructed afterward in the model rather than approximated on site with a pencil mark. The alternative is measuring a curve by hand while standing on the step it curves around.
Spiral stairs run on a separate set of numbers, with a tighter walkline radius, shallower treads, taller permitted risers, and lower headroom than a conventional flight. The one that changes how you capture is the requirement that treads be identical rather than merely within a tolerance, which leaves no margin at all for a scan to adjudicate. Look up that subsection before you measure one.
The same rule applies: scan to get the overall shape, then use a tape measure to check the code-required dimensions along the walkline.
Does an existing stair have to meet current code?
Not always, and this matters if you are documenting rather than building.
The IRC carves out an exemption for altered stairs where the surrounding space and construction leave no room to make the pitch shallower. A staircase measuring outside today’s limits is not automatically a violation, and a renovation does not automatically trigger a rebuild.
This changes the purpose of your measurement. For a new stair, you check whether it meets code. For an existing stair, you are usually just recording what is there, so the person planning the work knows the real dimensions before deciding what can be changed. Scanning is great for this kind of documentation.
What is the best tool for measuring stairs?
People often buy a terrestrial scanner for this job, but it is usually more than you need. For heritage stairs, structural investigations, or projects that need millimeter accuracy, it is worth the investment. But for most renovations, where you just need the stair mesh and to check the risers, a phone and a tape measure work much faster.
Turning the Capture Into a Deliverable
The scan shows what you measured, but it is not the final product. The format you send depends on who will use it.
A fabricator needs the opening geometry and, on a winder, the walkline. A layered DXF gives them editable linework, not a picture. A modeler bringing the stair into Revit needs the point cloud: export LAS, convert it through Autodesk ReCap, and link the result as a reference to model against. A client or building department wants a PDF, readable without software.
Whatever goes out, send the hand-verified numbers alongside it and note which dimensions came from a tape and which from the model. The recipient can't tell otherwise, and the distinction matters most for the dimensions that determine compliance.
Format choices for the handoff are covered in Point Cloud Export Formats Explained.
Faster than a tape measure.
FAQ
What is the best way to capture stair dimensions safely?
Scan the flight rather than working on it with a tape. Walk the stairs once holding the device, and the model gives you total rise, run, width, headroom, and stairwell geometry. Then verify the individual risers and treads by hand, since code tolerances there are tighter than any scan.
Can I measure a staircase with my phone?
Yes, for geometry. A LiDAR-equipped phone captures the flight, the landings, and the surrounding stairwell to within half an inch on standard interiors, which is adequate for design reference, modeling, and fabrication planning. It is not adequate for verifying the 3/8 inch riser uniformity rule.
What is the 3/8 inch rule for stairs?
Within one flight, the tallest riser cannot exceed the shortest by more than 3/8 inch, and the same limit applies to tread depths. The rule exists because a flight with inconsistent risers is a trip hazard: your gait adapts to a step height, and a riser that breaks the pattern is the one that catches people.
How accurate does a stair measurement need to be?
It depends on the dimension. Total rise, run, and headroom tolerate normal measurement error. Riser and tread uniformity does not, because the entire allowable variation is 3/8 inch. Match the tool to the tolerance rather than using one method for both.
Do carpet and runners count in stair measurements?
No. The code measures between finished surfaces and excludes carpets, rugs and runners, so a stair that measures compliant before flooring goes down can fail afterward.
Can I check stair headroom with a scan?
Yes, and this is where scanning is strongest for stairs. The code minimum is 6 feet 8 inches measured from the tread nosing, and a half-inch measurement tolerance against an 80-inch dimension is under one percent. A single walk-through lets you check clearance at every nosing afterward instead of spot-measuring overhead mid-flight.
Can you scan a winder or curved staircase?
Yes, and it is one of the better arguments for scanning a stair at all. Winder tread depth is measured along the walkline, a curve the code places 12 inches in from the inside edge of the turn. Following that arc with a tape while standing on a tapering step is awkward and inconsistent. A scan captures the geometry so you can construct the walkline in the model afterward.
Why do stairwells scan badly?
They are narrow, enclosed, and visually repetitive, giving a scanner less distinctive geometry to track. Move more slowly than you would in an open room, capture the flight in one continuous pass, and include both landings so the flight anchors to the floors it connects.
