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Measure stairs for carpet the right way: how to get accurate rise, run, and width numbers, count steps and landings, apply the 10-15% waste factor, and convert it all to carpet yardage with a worked example.
Ordering carpet for stairs is one of the few DIY measuring jobs where a small mistake gets expensive fast. Unlike a rectangular room, a staircase is a stack of angled surfaces, and carpet is sold in fixed widths by the square yard. Measure too little and the installer runs short mid-flight, which usually means reordering a whole extra width and living with a visible dye-lot difference. The good news: the entire job reduces to three numbers, the rise, the run, and the width of your stairs, plus one allowance, the waste factor. This guide shows you exactly where to put the tape on each step and how to convert the numbers into the yardage an installer or carpet store needs.
Carpet on stairs is installed as one continuous strip that wraps over each tread, rounds the nosing, and drops down the riser face to the next tread. So the unit of measurement is not the step, it is the strip length that covers one tread plus one riser plus the nosing wrap. For a standard step, that strip length equals the tread depth plus the riser height plus about 1 to 2 inches to wrap the nosing cleanly. If your tread is 10.5 inches deep and your riser is 7.5 inches tall, one strip is roughly 19 to 19.5 inches long. Multiply by the number of steps, and you have the total carpet length the flight needs. The width of each strip is simply the width of your stairs.
Rise. The vertical face of each step, measured from the surface of one tread straight up to the surface of the tread above it. Most residential stairs land between 7 and 7-3/4 inches. The International Residential Code caps risers at 7-3/4 inches (IRC R311.7.5.1), so if you read more than that, measure again, you may have hooked the tape on the nosing instead of the tread surface.
Run. The horizontal depth of each tread, measured nosing to nosing. The code minimum is 10 inches of tread depth (IRC R311.7.5.2), and the nosing must project between 3/4 and 1-1/4 inches (IRC R311.7.5.3). Hook your tape on the face of the riser below and read it at the nosing edge. If you want a refresher on how tread depth is defined, the tread depth calculator page walks through the nosing-to-nosing rule.
Width. Measure the full width of the stairs from wall to wall, or from the wall to the outer edge of the open side, at the widest step. Typical residential stairs are 36 to 44 inches wide. Carpet comes in 12-foot widths, so most staircases fit within a single width with no lengthwise seam, which is exactly what you want.
1. Use a steel tape measure, not a cloth tape or a phone app. You need 1/8-inch accuracy, and phone measuring tools drift on angled surfaces.
2. Measure every step, not just one. Risers and treads vary, especially in older houses, and carpet is cut per step. Record each tread depth and riser height in a two-column list, numbering the steps from the bottom.
3. Measure the rise from finished surface to finished surface. If old carpet or pad is still on the stairs, pull it up first or your numbers will be off by the pad thickness. Measure at the center of the step and note the tallest riser you find, then cut to that reading so every strip is long enough.
4. Measure the run nosing to nosing. Hook the tape on the riser face, extend across the tread, and read at the front edge of the nosing. Plan the nosing wrap separately: most nosings need 1 to 1.5 inches of extra strip length. The nosing calculator explains the 3/4 to 1-1/4 inch projection band if you want to check yours.
5. Measure the width at the top, middle, and bottom of the flight, and use the widest reading. Walls are rarely perfectly parallel, and the carpet is cut to the widest step.
6. Count risers and treads separately. A straight flight usually has the same number of each, but count them, do not assume. The top step is often the upper floor itself, which changes the count.
Landings. A landing is measured like a small room. Measure its length along the walking direction and its width across, then add that rectangle to your total. Plan the landing piece to come from one unbroken width of carpet so any seam sits at the edge of the landing, never in the middle where feet pivot.
Winders and pie steps. On stairs that turn with winders, measure each winder at its widest point and add roughly 20 percent extra length for those steps, since the angled cuts waste more carpet.
Bullnose starting steps. The curved first step is wider than the rest. Measure its widest point and add 2 to 3 inches so the curve wraps without a seam across the nosing.
Open stairs with a waterfall edge. If the carpet wraps over the open side of each tread, add the wrap depth to the strip width for every step.
The waste factor is not padding for sloppy measuring. It covers three real things. First, pattern matching: if your carpet has a pattern, each strip must start at the same point in the repeat, which eats length. Second, miscuts: one winder cut wrong, or one step wider than you thought. Third, the future: keep a remnant of 2 to 3 feet. If a tread wears through in five years, a patch from the same dye lot is invisible, while a patch from a new roll is not. For a straight flight with solid-color carpet, add 10 percent. For winders, patterns, or both, add 15 to 20 percent.
Carpet is sold by the square yard (9 square feet), in 12-foot-wide rolls. Here is the conversion with a worked example.
1. Strip length per step = tread depth + riser height + 1.5 inches (nosing wrap). Example: 10.5 + 7.5 + 1.5 = 19.5 inches.
2. Total length = strip length x number of steps. Example: 19.5 x 14 steps = 273 inches = 22.75 feet.
3. Area = total length x stair width, in consistent units. Example: 22.75 ft x 3.5 ft (42 inches) = 79.6 square feet = 8.85 square yards.
4. Add the waste factor. Example: 8.85 x 1.10 = 9.7 square yards, so order 10 square yards.
If your stairs are wider than 48 inches, check with the store whether the strips still cut efficiently from a 12-foot roll. At some widths the cutting layout changes and the yardage math above understates the order. Skip the hand math with our carpet flooring calculator, which runs the strip-length and waste-factor math from your measurements.
For a straight flight in a solid color, 10 percent over your measured total. For patterned carpet or stairs with winders, 15 to 20 percent. The extra covers pattern repeats, cutting waste, and a remnant for future repairs.
Both, as one number. Carpet wraps the tread and the riser in a single strip, so add tread depth plus riser height plus about 1.5 inches for the nosing wrap. Measuring only the tread is the most common reason orders come up short.
Measure the actual width and use it in the yardage math. Most residential stairs are 36 to 44 inches wide and fit comfortably within carpet's 12-foot roll width. Above about 48 inches, confirm the cutting layout with your supplier, since wide strips can change how many strips fit across the roll.
Only if you have verified every step matches. In new construction they usually do, within an eighth of an inch. In older homes, assume they do not until you have measured them. Measure each step, cut to the largest readings, and you will never come up short.
After. Old carpet and pad add up to half an inch or more to every surface, which compounds across 14 steps into several inches of error. Strip the stairs to the wood or subfloor, then measure.
Measuring stairs for carpet takes about twenty minutes with a tape measure and a notepad, and it is the cheapest insurance in the whole project. Rise plus run plus nosing wrap, times the step count, times the stair width, plus ten percent. Bring those numbers to the store or the installer and the order is a five-minute conversation instead of a gamble.
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Calculations are for reference only. Always verify with local building codes.
