Measuring your stairs before you calculate
The calculator is only as accurate as the riser and tread numbers you feed it. Measure the physical stairs, not a plan drawing.
Measure two or three individual risers
Hold a tape flat against the vertical face of a riser, floor to floor. Measure at least two steps and average them — older or hand-built stairs are rarely perfectly uniform.
Measure two or three individual treads
Measure the flat horizontal depth of a tread from the back of the nosing above to the face of the riser below, not including any nosing overhang.
Count every step in the flight
Count from the bottom floor to the top landing, including the final step that lands on the upper floor. If your stairs already have a rise-and-run plan, pull the step count from there instead of re-measuring.
Pick your installation style and width
Waterfall uses less runner and is faster to install; captured (French cap) is tucked into each corner for a tailored look but uses slightly more material. Pick a stock width or enter a custom one.
The five calculations behind every result
Nothing on this page is a black box. Here's exactly what runs when you change a number.
Base Coverage
The runner climbs every riser face and crosses every tread on the way up. Treads = Steps − 1, the same convention used across this site's geometry tools.
Style Allowance
Waterfall lets the runner skim over each nosing. Captured presses it into the inside corner of every step, which consumes a small, editable tuck allowance per step.
Overage
Extra length to wrap or tuck the runner at the top landing and to turn it under or let it pool slightly at the bottom floor.
Waste / Contingency
A flat percentage on top of the physical coverage, covering measuring error, pattern matching, and a leftover remnant for future repairs.
Yardage
Converts the linear total into square yards, the unit carpet is most commonly priced and ordered in.
Walking through a real 14-step flight
Same five calculations, filled in step by step, for a 14-step stair with a 7.71" riser and 10" tread — the default this calculator loads with, matching the site's Stair Rise and Run Calculator example.
Base coverage
14 steps means 14 risers and 13 treads. Base = (14 × 7.71) + (13 × 10) = 107.94 + 130 = 237.94".
Overage
Add a 12" top overage and a 6" bottom overage: 237.94 + 18 = 255.94". At this point the style choice hasn't been applied yet — that's next.
Waste allowance
With the default Waterfall style (0 added) and a 10% contingency: 255.94 × 1.10 = 281.53", or about 23.5 feet — comfortably under a 25 ft splice limit, so no seam is needed.
Switching styles changes the splice outcome
Switch to Captured with the default 1.5"/step tuck allowance instead: Style Allowance becomes 14 × 1.5 = 21", pushing the pre-waste subtotal to 276.94" and the final total to (276.94 × 1.10) ≈ 304.6", or about 25.4 feet. That alone crosses a 25 ft splice limit — the same stair now needs a seam purely because of the installation style chosen, which is exactly the kind of interaction worth checking before you order.
This is why the splice chip below is worth watching whenever you toggle installation style, not just when you change the step count — a style switch alone can tip a borderline order over a roll-length limit.
Waterfall vs. captured vs. bullnose/pleated
All three are valid ways to lay a runner over open-back or closed treads. They trade material use against fit and visual crispness.
| Style | How it's fitted | Material use | Best for |
|---|---|---|---|
| Waterfall | Falls straight down the riser face, passes over the next nosing without being pressed into the corner. | Lowest | Fast installs, thicker pile that resists a crisp fold. |
| Captured / French cap | Pressed and tucked into the inside corner of every step for a tailored, fitted look. | Base + tuck allowance | Formal staircases, thinner or flatter weaves. |
| Bullnose / pleated | Wrapped around a rounded starting step and pleated to follow a curved or bullnose nosing. | Base + extra for pleats | Curved starting steps only — not covered by this calculator's straight-flight math. |
Need full wall-to-wall stair carpet instead of a centered runner? Use the Stair Carpet Calculator.
Common stock widths and formats
Runner is sold two different ways, and it changes how you should read the total length this calculator gives you.
| Width | Typical format | Notes |
|---|---|---|
| 27" | Cut-to-order roll or pre-bound rug | Common on narrower stairs and traditional runners. |
| 30" | Cut-to-order roll or pre-bound rug | A middle-ground width many suppliers stock. |
| 32" | Cut-to-order roll or pre-bound rug | This calculator's default width. |
| 36" | Cut-to-order roll or pre-bound rug | Common on wider stairs, leaves a narrower side border. |
[VERIFY] Exact stock widths, maximum continuous roll lengths, and whether a product is sold cut-to-order or as a fixed pre-bound rug all vary by manufacturer and retailer — confirm with your specific supplier before ordering. Pre-bound rugs are typically sold in fixed lengths, so you'll size up to the next available length and trim, rather than ordering the exact calculated total.
Padding, fasteners & ordering considerations
A correct length is only part of a finished runner install — three more decisions affect the final result and the order.
Padding underneath
Most installs use a thin, dense stair-specific pad under the runner for cushioning and to protect the backing from the sharp nosing edge. Padding is bought and cut separately — use the Stair Runner Padding Calculator for that yardage.
Fasteners
Hidden tackless strip or staples are the modern default. Decorative stair rods sit visibly in the crook of each step and are especially common with captured/French cap installs, where they also help hold the tuck in place.
Seams
If your total exceeds your supplier's max continuous length, a joining seam is usually placed on a riser face rather than a tread, where foot traffic and light both make it less noticeable.
Why order extra
Beyond covering measuring error and pattern matching, the waste allowance leaves a small leftover piece from the same dye lot — useful if a section is ever damaged and needs an invisible patch years later.
These are planning-stage estimates for a straight flight. Winder, curved, or bullnose starting steps need a per-step measurement rather than this uniform formula.
Common mistakes when calculating runner length
Most short orders and mid-install surprises trace back to one of these five planning errors.
Measuring nosing-to-nosing instead of tread depth
Including the nosing overhang in your tread measurement inflates the total. Measure the flat tread only, the same way the riser and tread inputs are defined here.
Skipping the top and bottom overage
Forgetting the wrap allowance at the landing and the bottom floor leaves no material to finish either end cleanly, even though the mid-flight math was correct.
Ordering waterfall yardage, installing captured
Switching installation style after ordering is one of the most common reasons a runner order comes up short — see the worked example above for exactly how much that swing can be.
Assuming a straight flight on winder or curved stairs
This calculator assumes uniform riser and tread dimensions. Winder and curved stairs have treads that vary in depth across the stair and need individual per-step measurements instead.
Zeroing out the waste allowance
Ordering the bare calculated minimum leaves no room for measuring error, pattern alignment, or a future repair patch — a 10% contingency is inexpensive insurance against a second order.
When to use a stair runner length calculator
Runner length planning comes up any time a centered strip of carpet is being added to an existing or new staircase.
Replacing worn carpet
Sizing a like-for-like replacement runner on an existing staircase.
New construction
Ordering runner ahead of move-in for a newly built staircase.
Adding grip over hardwood or tile
Covering slick finished stairs with a runner for traction and sound.
Sizing a pre-bound stair rug
Finding the next available fixed length up from your exact total.
Cross-checking an installer's quote
Sanity-checking the yardage a flooring contractor has quoted you.
Budgeting a future repair
Confirming enough contingency yardage is kept aside from the same dye lot.