How To Measure Stairs For Carpet: Carpet Calculator

Before you can put in new carpeting in your home, there are numerous decisions you must make. You have to choose the style, weave, and color. But other considerations also come into play, like how durable the carpet is and how much you need. To figure out if your budget covers your options, you’ll likely want to know how to measure stairs for carpet.

In general, you can measure stairs for carpeting by using the equation width x ((run + rise + nose) x number of stairs) = area. However, calculating how much carpet you need varies based on the stair type, shape, and size, as well as the configuration of your staircase.

In this article, we’ll show you how to measure a staircase for carpeting. However, you may want to contact a professional carpet installer for help if you have a unique staircase configuration.

How To Measure Stairs For Carpet

How to Measure Carpet

How much space you intend to carpet is a massive factor in your budget. Carpets often come by the square foot or the square yard, so you will need to calculate the square footage or the area you want to carpet.

You can measure carpet by focusing on each area and multiplying the width times the length, then adding the area totals together. However, measuring for stairs requires slightly different steps. You’ll need to consider the height or rise and length or run of each step.

Stairs also come in varying shapes and sizes. The primary stair types include:

  • Box stair: The standard, simple staircase, box stairs have a tread and a riser with no fancy embellishments. They’re typically 10 inches deep by 8 inches tall, which is a total of 18 inches of surface space per stair.
  • Cap stair: A cap stair is open on the side with railings. They typically have the same length as box stairs, but you need an extra foot of width to wrap the carpet around the posts and frame the stair’s edge. However, you could opt to stop the carpet before the railing posts instead.
  • Pie stair/winder: A pie stair is a triangle-shaped stair you sometimes see wrapping around a corner or winder. They’re not usually measured based on their exact shape, so account for 48 inches by 30 inches for each winder. It’s also best to have a professional install carpeting on pie stairs and winders, as you want the grain of the carpet to align with the other stairs seamlessly.
  • Open stair: Sometimes called a Hollywood stair, open stairs have no backing. People don’t usually install carpet on open stairs, but you can cover them with no less than 20 inches of the carpet by multiplying the step height by 2 to wrap the carpeting around the step entirely.
  • Bullnose: The bullnose stair is at the bottom of a staircase. They’re wider than the rest of the steps and often rounded on one or more sides. The riser and tread are the exact sizes as box stairs, but the width is substantially wider.

How To Measure Stairs For Carpet

Calculating becomes a bit more involved for stairs than a traditional square room. However, the process is doable even for beginners. Properly installing carpet on stairs comes down to taking the correct measurements. To find the square footage of your stairs, we’ll use the following equation:

  • Width x ((run + rise + nose) x number of stairs) = area

The equipment you need includes a flexible tape measure and either a calculator or a piece of paper and pencil to compute the numbers. Use the detailed step-by-step instructions below.

Step 1: Measure the Run

Start by measuring the run of the top step. Sometimes the run is also called the length or tread of the step. It’s the area where you step your feet.

Standard staircases have a tread that’s 10 inches deep. However, it’s best to measure your stairs in case they are not the same size. Cap stairs with railings require an extra foot carpet to wrap around the posts, and double cap stairs require an extra foot on each side.

Measure the tread’s depth, with the tape measure extending to the outer edge of the step. Write down the number.

Step 2: Measure the Rise

The rise of each step is the height, fall, or distance between each stair. It’s the part your foot bumps against if you trip or the flat part at the back of the stair. Most risers are 8 inches tall in standard, straightforward staircases.

Keep in mind that you should have one more riser than treads, which accounts for the uncarpeted top stair that leads into your upstairs hallway.

To find the stair’s rise, hold the end of a flexible tape measure in place at the bottom of the step. Run it along the front face and across the flat top until you touch the bottom of the next stair. Copy down the number.

If your stairs have a lip, measuring the rise could be more difficult. Try asking someone to help you. Have one person hold the tape measure under the lip for an accurate reading of the rise distance for each stair.

Step 3: Add the Rise and Run Together

Next, add the rise and run together. Include an extra inch or two to account for wrapping the carpeting around the nose of each stair and padding bulges.

Step 4: Multiply by the Number of Stairs

Count to see how many stairs you plan to carpet. Multiply the number of stairs by the number from step 2 (the rise and run of your stairs). Round to the nearest foot.

Step 5: Convert to Feet

To convert the number in feet (if you haven’t already), divide your answer from step 3 by 12 and round up.

Step 6: Measure the Width

Use a tape measure to get the width of your staircase. The width allows you to know how wide the carpet should be. Copy down the number, rounding up to the nearest foot or adding an inch or two of leeway.

Step 7: Multiply Width by Length

Multiply the width or answer from step 5 and the length from step 3. The answer is the square footage of carpet you need for the stairs.

Step 8: Add in Landings

Take any landings into account next. While most landings are square, you may need a professional’s help to account for odd-shaped landings. Measure the length and width of your landing, multiplying the numbers together to find the square footage.

For example, 4 by 5 feet is a standard landing size. Round the landing measurements to the nearest foot for the best results.

Step 9: Add it All Together

Add the answer from step 8 to your previous calculation from step 7. The result is the square footage or area of carpeting you need to cover the stairs and landing entirely. If you want to include carpet padding, add an extra 3 inches to the total area and round to the nearest foot.

How to Use an Calculator

An easier way to calculate how much carpet you need is to use an online tool rather than complete the math by hand. For example, the Home Advisor carpet calculator is quick and free to use. Improvenet has another excellent carpet calculator for rooms and stairways.

All you have to do is determine the length and width of a stair for Area 1 and include the measurements for landings or any other sized stair in Areas 2, 3, or 4. Enter the number of stairs. The calculator shows the total area size and total carpet you need automatically.

Finally, it would be best to add 10% to 20% to the final figure for waste.

Installing Carpet on Stairs

Carpet cost calculator

The carpet you install on stairs must run in the direction of the pile or traffic flow. In other words, you install the carpet from top to bottom rather than side to side.

Many people use the waterfall method to install carpet on standard box stairs. The technique uses a single continuous piece of carpet to cover each step from riser to tread. It’s ideal if you have uniform steps and possibly a basic landing. If you have a circular or a unique setup, the process is much more complicated.

However, most stairs today have features like bullnose steps and cap stairs that don’t allow you to install the carpet in a single piece. These calculations take great care and attention to detail. You typically need to install the carpet on each stair or landing separately.

Building codes also vary by region, so you could have stair sizes different from the standard. This is especially true if your stairway is custom-built. Taking careful measurements helps ensure fewer mistakes.

How to Figure Out Carpet Waste

Once you have the measurements, you want to account for carpet waste. You will have more carpet waste than other flooring types because of the standard roll sizes. It’s impossible to install carpet on stairs without trimming or making a few adjustments, so having a little more material than you need helps account for mistakes or oddities.

Add 10% to 20% of your total carpet area to account for carpet waste. Expect at least 10% waste when you measure for carpet. For a unique layout, go with 20%.

When Do You Need to Hire a Professional?

If you have a circular, irregular, or unique setup, consider hiring a professional to install the carpeting. Any configuration out of the ordinary may require an installer for the best results.

Most professionals will take their measurements, but having the exact measurements when you head to a warehouse or hire a professional installer allows you to compare prices and shop around for the best rates. You don’t want to be surprised by the cost later.

When you hire a carpet pro, you pay for the actual square feet installed, with only 10% accounted for overage or waste. Labor costs vary based on the company.

How is Standard Carpet Sold?

Carpet rolls come in two standard widths: 12 and 15-foot-wide rolls. You may also be able to find uncommon roll sizes, like 13.5-feet-wide. One square foot of carpet is a foot long by a foot wide, so there are nine square feet in a square yard of carpet.

However, the roll length is not standard.

How Much Padding Do I Need?

Carpet padding is typical in residential areas. It protects the bottom of the carpet and prolongs its lifespan. However, you probably won’t install padding in humid regions or rooms like a basement. The padding type also depends on your needs.

In general, you need the same amount of padding as carpet. This is another crucial reason your calculations must be correct.

Padding allows the carpet to last longer on a staircase. It can also help absorb sound from squeaky stairs. When you install the padding on stairs, keep in mind that the padding is a couple of inches short from the wall to account for tack strips, holding the material in place.

Carpet padding costs between $200 and $500 for an average-sized room. Professionals include the price of installing padding in their initial bid.

How Much Carpet Do You Need to Repair Tears or Pet Damage?

If the carpet on your stairs needs repair, whether from pet damage or tears over time, replace the area. Measure the entire damaged area, avoiding the seams. A 4-inch incision in the middle of a step would require enough carpet to stretch the whole stair or the next available hem, for example.

If you pay a professional to repair your carpet, you might be able to ask for an invisible seam repair. The process requires less replacement carpet. However, it’s not available for every carpet type.

How to Measure Stairs for a Carpet Runner

Stair runner calculator

If you want to install a carpet runner on your stairs, the process is much easier – even for winding staircases. Stair runners come in many colors, patterns, and styles.

To measure a staircase for a runner, start by measuring the length and width of your stairs. Rather than measure every step, find the measurements for the tread and riser of your first step. Leave at least a 5 cm gap along the sides.

Find the tread and riser measurements, adding them together. Multiply by your number of stairs for the total carpet needed for your stairs. Remember to exclude the top step unless your carpet running continues across the floor.

Next, measure any landings and add this to the overall length measurement. Add everything up and include an additional 10% to the total for errors.

How to Find Outdoor Carpet Measurements

To find the measurements for outdoor carpet, calculate using the same steps above. Multiply the length and the width, adding a few extra inches to wrap around a patio’s edge. Most indoor/outdoor carpets cost around $3.50 per square foot.


Like measuring rooms for carpet installation, stairs require you to find the length and width of each surface area for the total carpet amount you need. Finding the proper calculations becomes more confusing with unique configurations or stair shapes and sizes outside of the norm. Knowing your measurements helps you whether you hire a professional installer or not.

Did our step-by-step instructions help you measure your stairs for carpet? If you found our directions helpful, please share the article with your friends and family. Let us know how your carpet installation went in the comments.


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