How to Build Stairs — Calculating Rise and Run Guide for Eastern Washington Homeowners & Contractors

Getting the Math Right: How to Calculate Rise and Run

If you’ve ever walked up a staircase that felt “off”—where your foot came down a little too early or too hard—you experienced what happens when rise and run aren’t calculated correctly. This is the single most important part of any stair project, and it’s where we see the most questions from customers walking into our Airway Heights, Colville, and Kettle Falls locations.

Understanding Rise vs. Run

Rise is the vertical height of each step. Your total rise is the full floor-to-floor height, measured from the finished surface below to the finished surface above—not the subfloor, not the framing, the actual finished floor.

Run (also called tread depth) is the horizontal depth where your foot actually lands. Your total run is the tread count multiplied by the tread depth, plus the bottom tread overhang.

Step-by-Step Calculation

Here’s the process we walk customers through at the counter:

Measure total rise from finished floor to finished floor, in inches.
Divide by a target riser height, typically 7″ to 7¾” for residential stairs. Round to the nearest whole number—that’s your riser count.
Recalculate actual riser height by dividing total rise by that riser count. Every riser in the flight needs to match this number within 3/8″.
Determine tread depth (run) using a comfort formula: 2 × rise + run should land somewhere around 24″–25″. Most Eastern Washington builders settle on a 7″ to 7½” rise paired with a 10″ to 11″ run.
Calculate stringer length using the Pythagorean theorem: stringer length = the square root of (total rise² + total run²). This tells you how long your stringer lumber needs to be before cutting.

A framing square with stair gauge attachments makes this layout process much easier and more accurate than eyeballing it. We stock these at all three locations, along with story poles that let you mark out your riser increments before you ever pick up a saw.

A Real-World Example

Say you’re building deck stairs with a total rise of 84″ (7 feet) down to a concrete patio. Divide 84 by 7.5 and you get 11.2—round to 11 risers. Divide 84 by 11 and your actual riser height is 7.636″, which is under the 7¾” maximum and well within a comfortable range. Pair that with a 10.5″ tread depth, and you’ve got a stair that’s comfortable, safe, and code-compliant.

Eastern Washington Code Requirements You Need to Know

Washington State follows the 2021 IRC (International Residential Code) with some local amendments, and Spokane County and surrounding jurisdictions enforce these consistently. Here’s what applies to most residential stair projects in our area:

Rise and Run Limits

Maximum riser height: 7¾”
Minimum tread depth: 10″ (with nosing) or 11″ (without nosing)
Maximum variation between the tallest and shortest riser or tread in a single flight: 3/8″
Minimum stair width: 36″
Minimum headroom: 6’8″ measured vertically from the tread nosing

Some Washington code sections reference a broader acceptable range—rise of 4″ to 8″ and run of 9″ or more—for certain stair applications, but that 3/8″ uniformity rule is non-negotiable no matter which range you’re designing within. Inspectors in Spokane, Stevens County, and Ferry County check this with a simple measuring tape, and it’s one of the most common reasons a stair fails inspection.

Handrails and Guards

Any stairway with four or more risers requires a handrail on at least one side, mounted 34″ to 38″ above the tread nosing. If your stair or landing sits more than 30″ above grade at any point within 36″ horizontally, you also need a guard (a railing system at the open edge)—minimum height 36″ for guards.

Spokane County’s stair tip sheets reinforce these same numbers, so if you’re pulling a permit locally, expect your inspector to check riser uniformity, handrail height, and guard placement closely.

Landings

Code requires level landings at the top and bottom of any stairway, generally at least as wide as the stair itself and a minimum of 30″ deep in the direction of travel. This matters more than people expect—we’ve seen DIY projects get held up at final inspection because the bottom landing was undersized or sloped the wrong direction.

Building for Eastern Washington’s Climate and Terrain

Stair math is the same everywhere, but building durable, safe stairs in the Spokane area means accounting for our specific climate. Between hard winter freeze-thaw cycles, dry summer heat, and the frost-susceptible soils common across Spokane County, Stevens County, and Ferry County, exterior stairs take a beating that interior stairs never see.

Winter Freeze-Thaw and Ice

Our winters bring repeated freezing and thawing, which is hard on both wood and concrete. Water that gets into end grain or fastener holes on untreated lumber will expand and contract, accelerating rot. For any exterior stair—deck stairs, porch stairs, or stairs leading to a walkout basement—we strongly recommend pressure-treated lumber rated for ground contact if the stringers touch concrete or soil, even indirectly.

Ice on treads is a real safety issue here too. Consider composite decking treads with built-in texture, or add slip-resistant nosing strips to wood treads, especially on north-facing stairs that stay shaded and icy longer after a storm.

Dry Summer Heat and UV Exposure

On the flip side, our hot, dry summers cause exposed wood to check and crack if it isn’t properly sealed or finished. Green or wet lumber is especially problematic—as it dries out over a hot Eastern Washington summer, stringers can warp and twist, throwing your carefully calculated risers out of uniform. Always build with kiln-dried, properly seasoned lumber, and re-check your layout before final assembly if the lumber sat outside for any length of time.

Frost-Susceptible Soils

Many properties around Spokane, Colville, and Kettle Falls sit on soils that heave with frost. If your exterior stairs land on a concrete pad or footing, make sure that footing is poured below the local frost depth. A landing that heaves even half an inch out of level will throw off your bottom riser height and create a trip hazard—plus it looks bad and can crack concrete over time. On sloped lots, which are common throughout the region, a properly engineered concrete landing and pier system beats a surface-set stringer resting on patio blocks every time.

Drainage Matters

Water pooling at the base of exterior stairs is a recipe for ice in winter and rot in wood components year-round. Slope landings slightly away from the house and make sure gutters or downspouts aren’t dumping water right at your stair base.

Common Mistakes We See (And How to Avoid Them)

After decades serving builders and homeowners across Eastern Washington, our team has seen the same handful of mistakes come up again and again.

Measuring From the Wrong Surface

The most frequent error: measuring total rise from subfloor to subfloor instead of finished floor to finished floor. If you forget to account for flooring thickness—say you’re adding 3/4″ hardwood or tile later—your top or bottom riser ends up out of spec. Always measure finished-to-finished, and if flooring isn’t installed yet, add its thickness into your math now.

Forgetting Tread Thickness at the Bottom Cut

If your treads are 1½” thick, your bottom stringer cut needs to be shortened by that same amount, or your first step will be taller than the rest—an easy way to violate that 3/8″ variation rule and create a stumble hazard right where people are least expecting it.

Cutting All Stringers Before Testing

Small errors compound over multiple risers. We always recommend cutting one stringer first, test-fitting it in place, and confirming headroom, landing depth, and overall run before cutting the rest. A story pole marked with your riser increments makes this dramatically easier and catches mistakes before they become expensive.

Using the Wrong Lumber for Exterior Applications

Non-treated lumber touching concrete or soil is asking for trouble in our climate. Pair that with our freeze-thaw cycles and you’re looking at premature rot within a few seasons. Pressure-treated lumber, along with hot-dipped galvanized or stainless steel fasteners, is worth the extra cost for any stair exposed to the elements.

Skipping Headroom and Width Checks

It’s easy to get so focused on rise and run that you forget to verify 6’8″ of headroom and 36″ of clear width along the entire stair run. Measure this before you start cutting—reframing a stairwell after the fact is a much bigger job than adjusting your stair layout up front.

DIY or Call a Pro? Here’s How to Decide

We sell to plenty of confident DIYers and to professional contractors alike, and honestly, both approaches make sense depending on the project.

Good DIY Projects

Straight interior stairs with simple, well-documented framing
Deck or porch stairs with 3 to 6 risers landing on a concrete pad or paver base
Projects using prefab stair stringers or stair kits with manufacturer instructions

If you’re comfortable with basic geometry, can read a code table, and have room to work with proper headroom and landing space, a straightforward stair project is very doable with the right tools and materials from our stores.

When to Call a Local Contractor

Winder stairs, L-shaped or U-shaped layouts, or spiral stairs
Any stair serving as primary egress in a multi-story home, where stricter code requirements apply
Stairs tied into structural framing, foundations, or requiring new footings
Exterior stairs on steep or frost-prone sites requiring engineered concrete work

If you’re not sure which category your project falls into, it’s worth a call to your local building department—Spokane County, Stevens County, and Ferry County staff are generally happy to clarify code questions before you start. And if you’re mid-project and hit something unexpected, our staff at Airway Heights, Colville, and Kettle Falls have seen just about every stair scenario Eastern Washington terrain can throw at a builder.

What It Typically Costs and What Drives the Price

Stair project costs vary widely based on a few key factors:

Complexity

A straight single-flight stair is the most economical option. Adding landings, direction changes, winders, or custom guard systems increases both material and labor costs significantly.

Interior vs. Exterior

Exterior stairs cost more due to pressure-treated lumber, concrete landing work, corrosion-resistant fasteners, and weather-resistant finishes—all necessary given our climate swings.

Material Choice

Basic pressure-treated wood: most economical
Composite decking treads: higher upfront cost, less long-term maintenance
Steel or aluminum stair systems: higher material cost, often less labor-intensive to install
Interior hardwood treads: premium cost for finished appearance

Site Conditions

Excavation, frost-depth footings, drainage corrections, or demolishing an existing stair all add to the bottom line. Sloped Eastern Washington lots often need more site work than flat ones.

Our recommendation: get two or three local bids before committing to a professional build, and make sure each bid specifies exact riser/tread dimensions, materials, and whether concrete and railing work are included. If you’re going the DIY route, our team can help you price out lumber, hardware, and railing components for your specific rise and run calculations.

Ready to Start Your Stair Project?

Whether you’re building deck stairs for a new patio in Airway Heights, replacing a weathered porch staircase in Colville, or tackling an interior remodel near Kettle Falls, getting the rise and run calculation right is what separates a stair that feels safe and comfortable from one that doesn’t. We stock pressure-treated lumber, framing squares with stair gauges, composite decking, galvanized and stainless fasteners, and railing systems built for Eastern Washington’s climate at all three of our locations. Stop by Airway Heights, Colville, or Kettle Falls, or shop our building materials online to get everything you need for a code-compliant, long-lasting staircase.