Guide · For the trade
How to measure stairs for carpet, and the rest of the site measure
To measure stairs for carpet, count the risers, then measure one tread depth including the nosing and one riser height, add them, and multiply by the riser count: a 13-riser stair with 11 inch treads and 7 1/2 inch risers needs about 20 inches a step, 21 1/2 feet of carpet, plus a foot at each end and one extra step for waste, so 24 feet for a runner. Measure the width of the stair at the narrowest point and note every landing, winder, open side and bullnose step separately, because each one changes the cut. For wall-to-wall on the stair, the same length comes off a 12 foot roll and is cut into tread-width strips.
This is the guide for the designer or junior sending us a preliminary measure before our installer makes the final one. It covers the stair measure step by step, the parts of a stair that catch people out, measuring a room for broadloom and a room for a rug, and the numbers clients ask about.
What the designer measures and what the installer measures
Two measures happen on every job. Yours is the preliminary one: enough for a quote, a sample order and a schedule. Ours is the installer's site measure, which sets the order quantity and is the one we cut to. Sending a good preliminary measure does not make the site measure unnecessary, but it does make the quote accurate and the sample list right the first time. The carpet calculator guide turns room measurements into square yards; this guide is about getting the measurements themselves.
How to measure stairs for carpet, step by step
- Count the risers from the lower floor to the upper floor, including the top riser onto the landing or hall. A stair has one more riser than treads you can stand on.
- Measure one tread from the back of the tread to the front edge of the nosing, and one riser from tread to tread. Check two more steps; if they differ by more than 3/8 inch, note it for the installer.
- Add tread and riser, add 2 inches for the wrap under the nosing, and multiply by the riser count. That is the stair length.
- Measure the width of the stair at the top, middle and bottom, between the wall and the stringer or the wall and the baluster line. Note which sides are closed, open or spindled.
- Measure each landing as a small room, length and width, and note which way the stair leaves it.
- For winders or a curved flight, measure each tread at its widest point and photograph the flight from above.
- Note the bottom step: a bullnose or a curtail step with a rounded end needs extra width to wrap.
Send the riser count, the two unit dimensions, the width, the landing dimensions and the photographs, and we can quote a runner or wall-to-wall on the stair the same day.
Three stairs, measured
| Stair | Risers | Per step (tread + riser + wrap) | Runner length to order | Wall-to-wall off a 12 ft roll |
|---|---|---|---|---|
| Straight, 12 steps | 12 | 20 in | 20 ft plus 2 ft for ends and waste: 22 ft | 22 ft cut, strips at stair width |
| Straight, 13 steps | 13 | 20 in | 21 ft 8 in plus 2 ft: 24 ft | 24 ft cut |
| Two flights with a 4 by 4 ft landing | 7 plus 7 | 20 in | Two runs of 12 ft 8 in plus the landing: 29 ft, pattern repeat extra | Landing cut separately, pile direction matched |
A patterned runner adds one repeat per cut, so a two-flight stair with a landing adds two repeats; the pattern match guide explains the arithmetic. The stair carpet guide covers which constructions take the nosing wrap.
Runner width and the reveal
Runners come 27, 32 and 36 inches wide. On a 36 inch stair a 27 inch runner leaves 4 1/2 inches of tread showing each side; a 32 inch runner leaves 2 inches, which is tight; on a 42 inch stair a 32 or 36 inch runner is the proportion. Measure the width at the narrowest point and subtract 8 to 10 inches for the runner. If the stair is open on one side, the runner usually stops at the baluster line and the open edge is finished as a wrapped wall-to-wall return instead; say which you want. The stair runner width guide works through the choices.
Measuring a room for carpet
Measure the room at its longest and widest points, into doorways and closets, and add 3 inches each way for trimming. Note the direction you want the pile to run, usually toward the main window or down the length of the room, and where seams would be acceptable. Broadloom comes 12 feet, 13 feet 2 inches and 15 feet wide; a room wider than the roll needs a seam, and the measure should tell the installer where it can go. Closets off a bedroom are measured with the bedroom so they come from the same roll. Bay windows, fireplace hearths and built-ins are measured as rectangles that are subtracted later, not as odd shapes.
How to measure for a rug
Measure the room, then the furniture group the rug serves, not the room alone. For a living room, the sofa and chairs with their legs positions; for a dining room, the table with the chairs pulled out 24 inches; for a bedroom, the bed and nightstands. The rug should take the front legs of seating and leave 18 inches of floor at the walls, 12 inches in a small room. Standard sizes are 5x8, 6x9, 8x10, 9x12, 10x14 and 12x15; if the room lands between sizes, a custom size cut and bound from broadloom is 3 to 5 weeks. The area rug size guide has the room-by-room tables.
Questions designers ask
What is the 25 rule for stairs?
Two risers plus one tread should total 24 to 25 inches for a comfortable stair, so a 7 inch riser goes with an 11 inch tread. It matters to the carpet because pad and carpet thickness change the first and last riser by their combined depth, and code allows only 3/8 inch of variation in a flight. A thin stair pad keeps the stair inside the rule.
How long should carpet be for 13 stairs?
About 24 feet of runner: 13 risers at roughly 20 inches each, plus a foot at each end and one extra step for waste. A landing, a bullnose bottom step or a pattern repeat adds to that.
What is the 27 rule for stairs?
It refers to the 27 inch runner, the traditional width for a residential stair, which leaves 4 to 5 inches of tread exposed each side on a 36 inch stair. It is a proportion, not a code. Wider stairs take 32 or 36 inch runners by the same logic.
How much carpet for 12 steps?
About 22 feet of runner, or a 22 foot cut off a 12 foot roll for wall-to-wall, which is enough for the stair width strips plus the waste. Add the landing as a separate small room if there is one.
Does the designer's measure replace the installer's?
No. Yours sets the quote and the samples; the installer's site measure sets the cut and is the one the order is written from. Both happen on every project, anywhere in the country.
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