How to Calculate Stair Runner Length

Use the additive formula — tread depth + riser height per step, plus top and bottom landing overhangs — to get the correct lineal footage for your carpet runner order. This guide explains the formula, shows a 14-tread worked example, and compares runner widths by brand.

Stair Runner Length Reference Table

The table below uses standard residential stair geometry — 11-inch tread depth ( IRC §R311.7.5.2 ↗ minimum) and 7-inch riser height (within the IRC §R311.7.5.1 ↗ maximum of 7-3/4 inches) — with a 6-inch overhang at both the top and bottom landing. These are industry practice dimensions; measure your actual stair before ordering. Add 10–20% waste to the lineal feet figure before purchasing.

Source: CRI 105 §6 (Carpet and Rug Institute Standard for Installation of Residential Carpet — Stairs section) additive formula. Tread/riser dimensions per IRC §R311.7.5 ↗ (standard residential). Overhangs (6" top + 6" bottom) are industry practice — verify with your installer. Lineal feet rounded to nearest foot. Waste-adjusted order quantity uses 15% midpoint; use 20%+ for patterned runners.

The Runner Length Formula (Additive, Not Diagonal)

A carpet runner follows the walking path — it wraps flat across the tread, turns the nose, and goes straight up the riser, step by step. That means every step contributes both its tread depth and its riser height to the total length needed. The formula, per CRI 105 §6:

Runner length formula (additive — CRI 105 §6):

  runnerLengthInches =
      (treadDepth × nTreads)
    + (riserHeight × nRisers)
    + topOverhang
    + bottomOverhang

  Where:
    treadDepth    = horizontal depth of each tread (inches)
    nTreads       = number of treads (steps)
    riserHeight   = vertical height of each riser (inches)
    nRisers       = number of risers (= nTreads for most residential stairs)
    topOverhang   = length runner extends past top step onto landing (inches)
    bottomOverhang = length runner extends past bottom step onto floor (inches)

  --- Worked example: 14-tread residential stair ---

  treadDepth    = 11 inches  (R311.7.5.2 minimum tread)
  riserHeight   = 7 inches   (within R311.7.5.1 max of 7-3/4 inches)
  nTreads       = 14
  nRisers       = 14
  topOverhang   = 6 inches   (industry practice)
  bottomOverhang = 6 inches  (industry practice)

  runnerLengthInches = (11 × 14) + (7 × 14) + 6 + 6
                     = 154 + 98 + 12
                     = 264 inches
                     = 22.0 lineal feet

  With 15% waste buffer:  264 × 1.15 = 303.6 inches ≈ 25.3 lineal feet → order 26 lineal feet
  With 20% waste buffer:  264 × 1.20 = 316.8 inches ≈ 26.4 lineal feet → order 27 lineal feet

Why NOT the Pythagorean formula? Many online "stair length calculators" return the stringer length — the diagonal board that forms the structural spine of the staircase. The stringer is calculated as √(riserHeight² + treadDepth²) per step, which gives the hypotenuse of each step's right triangle. That number is shorter than the walking path because it cuts across the corner of each step. Using the stringer formula to order a runner will leave you 30–50% short of material. CRI 105 §6 is explicit: the carpet path is additive, not diagonal.

The 6-inch top and bottom overhangs are a common specification from manufacturer install guides (Natco, Mohawk). They provide the anchor point for the grip strip or staple pattern at each landing — without the overhang, the runner ends exactly at the nosing with no material to secure to the floor. If your stair has a full landing between flights, add the landing dimension to the total as a flat section.

Stair Waste, Bullnose Wrap, and Why Stairs Need 30% More Than Flat Rooms

1. Why Stair Waste Runs 10–20% (vs 5–10% for Flat Rooms)

Flat-room carpet waste comes from cutting around walls and fitting rectangular runs — typically 5–10% for solid colors and simple patterns. Stairs generate more waste per lineal foot for three reasons: (a) every tread-nose requires a trim cut that produces a small unusable piece; (b) directional pile means the runner must run continuously in one direction — you cannot flip and reuse off-cuts; (c) patterned or striped runners require the pattern to align across each step, consuming additional length at every match point. Industry practice (per Natco and Mohawk install guides) is 10–20% for solid-color and textured runners, and 20% or more for any patterned or striped design.

2. Bullnose and Nosing Overhang — Per-Tread Wrap Allowance

A bullnose tread — where the tread nose overhangs the riser below by 3/4 to 1-1/4 inches — adds a small amount of wrap material at each step. The additive formula already accounts for this if you measure your actual tread depth including the nosing overhang. Measure from the face of the riser below to the face of the riser above — that full horizontal distance is the tread depth to use in the formula. Do not measure to the nosing tip and then subtract; the runner wraps over the tip, so the full tread depth to the riser face is the correct input.

3. Runner Width — Exposed Edge and the 36-Inch Stair Standard

IRC §R311.7.1 ↗ sets the minimum residential stair width at 36 inches (measured between walls or handrails). Standard runner widths are 27 inches, 30 inches, and 36 inches. On a 36-inch stair: a 27-inch runner leaves approximately 4.5 inches of exposed tread on each side; a 30-inch runner leaves approximately 3 inches per side; a 36-inch runner covers the full tread width with no exposed wood edge — which reads as wall-to-wall carpet, not a runner. Most interior designers specify 3–4 inches of exposed tread on each side for the classic runner aesthetic. Measure your finished stair width, not the rough framing, before selecting a runner width.

Brand Comparison: Natco vs Mohawk vs Karastan Runner Widths

The three major stair runner brands sold at Home Depot and Amazon differ in available widths, material focus, and price tier. Width availability drives which runners fit your stair — confirm width in stock before ordering, as not all widths are stocked at all locations. Data from manufacturer product pages and HD/Amazon listings, 2026-Q2; verify availability at retailer before purchase.

Affiliate disclosure: CraftedCalcs earns commission on purchases made through the Home Depot and Amazon links below. The commission doesn't change your price. It helps us keep this site free.

Width data from manufacturer product pages and HD/Amazon listings (2026-Q2) — MEDIUM confidence; verify before purchase. Karastan runners are available at Home Depot specialty order; Amazon availability varies by style. Brand names referenced for descriptive purposes (nominative fair use). Natco® is a trademark of Natco Products. Mohawk® and Karastan® are trademarks of Mohawk Industries. CraftedCalcs is not affiliated with or endorsed by these manufacturers.

Stair Runner Cost Estimate — 2026-Q2 Reference

Carpet runner pricing varies significantly by material, pattern, and brand. The ranges below are from Home Depot and Amazon retail listings as of 2026-Q2 — verify at retailer before purchase, as pricing changes seasonally. Regional variation is typical. The estimates use 22 lineal feet (standard 14-tread stair) as the basis; adjust for your actual tread count using the reference table above.

Prices as of 2026-Q2; verify before purchase — pricing changes seasonally and varies by region. Installation labor (professional staple/grip-strip install) typically adds $3–8 per lineal foot in most markets. Use the Stair Calculator to determine your step count, then apply the runner length formula above for a material estimate.

Runner Measurement Checklist: Before You Order

These steps prevent the most common ordering errors on stair runner projects. All are pre-purchase decisions — a short measurement runs are far cheaper than a return and reorder.

1. Count your treads — not your risers. Most residential stairs have equal numbers of treads and risers, but verify by counting each. The formula uses treads × tread depth + risers × riser height. A common error is using only one count or confusing the two.
2. Measure actual tread depth and riser height — do not assume IRC minimums. Measure tread depth horizontally from riser face to riser face, including the nosing overhang. Riser height is measured vertically from tread surface to tread surface. Older stairs often have non-standard dimensions.
3. Add top and bottom overhangs before computing lineal feet. Industry practice is 6 inches at each landing. Without overhang material, there is no anchor point at the top and bottom of the run, and the runner will shift under foot traffic.
4. Apply the correct waste percentage for your runner style. Solid-color: add 10–15%. Textured or berber: add 15–20%. Patterned or striped: add 20% or more. Buying short on a patterned runner with a long lead time means the project stalls.
5. Confirm runner width against your finished stair width before ordering. A 27-inch runner on a 36-inch stair leaves 4.5 inches on each side — a 30-inch runner leaves 3 inches. Measure the finished width (not the rough framing) and decide your preferred exposed-edge margin before selecting a runner SKU.
6. Budget for padding separately. Rebond padding (3/8-inch or 7/16-inch) is ordered by lineal foot and installed under the runner. It is not included in runner pricing and adds approximately $1–2 per lineal foot to the total material cost.

Common Stair Runner Measurement Mistakes

These four errors account for most stair runner ordering problems, sourced from r/HomeImprovement and r/Flooring installer threads. Each is preventable at the measurement stage.

• Using the diagonal stringer length instead of the additive runner length. The stringer is the diagonal structural board calculated by the Pythagorean theorem. A runner follows the walking path — tread + riser per step. Using the stringer length will leave you 30–50% short of material, with the runner running out before the bottom of the stair. CRI 105 §6 uses the additive formula. Many online "stair calculators" return the stringer length — check which formula they use before trusting the output.
• Forgetting top and bottom landing overhangs. Ordering runner material to exactly match the step count with no overhang means the runner ends flush at the nosing of the top and bottom step. There is no material to wrap under and staple or secure to the grip strip. Industry practice is 6 inches at each end — add 12 inches total to your raw formula result before converting to feet.
• Skipping pattern-match waste on striped or patterned runners. A striped runner must align the stripe pattern across every tread. If the pattern repeat is 6 inches and your tread depth is 11 inches, not every tread will land on a full repeat — extra length is consumed to re-align the pattern. Ordering at 10% waste for a patterned runner produces visible pattern jumps at multiple steps. Budget 20% or more and confirm the pattern repeat length with the manufacturer before ordering.
• Ordering runner width equal to full stair width. A 36-inch runner on a 36-inch stair covers the full tread with no exposed wood — it looks like installed wall-to-wall carpet, not a runner. The standard runner aesthetic requires 3–4 inches of exposed tread on each side. On a 36-inch stair, a 27-inch or 30-inch runner achieves that margin; a 36-inch runner does not.
• Omitting the waste buffer entirely and ordering only the formula's yardage. The formula gives the theoretical minimum. Even a solid-color runner requires some margin for alignment, trim errors, and the occasional mis-cut. A 10% buffer adds roughly 2 lineal feet to a 22-foot order — well worth having on hand if you cut a tread piece short. There is no practical way to order a matching piece later if the dye lot has changed.

Frequently Asked Questions

Estimates and specifications in this guide are for informational purposes only. Verify all measurements with a tape measure and confirm with your installer before purchasing. See our full disclaimer.