How to Calculate How Much Carpet Is Needed for Stairs

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If you're planning to add carpeting to your home or replace existing carpeting, you need to know how much carpet to purchase. To determine how much carpet you need for a regular room, simply multiply the width by the length of the room. However, you'll need to take a few extra measurements to calculate stair carpet needs.


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What to Measure

Before you can measure for carpet, it's important to understand the terminology used to describe the parts of the stair you'll be measuring. The width is how wide each stair is from side to side. The run is the depth of the stair tread, or where you place your foot. The rise is the height of the stairs — the distance between the top of one tread and the tread below it. If your staircase's treads overhang the riser by an inch or two, this overhang is often called the nose or lip.


Things You'll Need

How to Measure Stairs for Carpet

Step 1: Measure the Rise and Run

Use a flexible tape measure to measure the rise and the run. If your treads have a nose, put the tape measure at the bottom of the step and run the tape measure up and around the overhang and then to the back of the tread for the most accurate measurement.

Step 2: Multiply by the Number of Stairs

Check your staircase to make sure you have an equal number of risers and treads. Staircases that lead down from a hardwood floor often have an additional carpeted riser above the top step that you must include in your calculations. If you measured the rise and run in inches, divide the result by 12 to get it in feet.


Step 3: Measure the Width of the Stairs

Stretch the tape measure from the left side of the tread to the right. Add 2 inches to the measurement to cover the edges. If you measured in inches, divide the result by 12 to get it in feet. Multiply the results of step 2 in feet by the width of the stairs in feet to calculate the square footage of carpet needed.

Step 4: Measure the Landings

If your staircase has landings, you must also measure them to get the correct estimate of carpet needed. Landings are typically square or rectangular, so you simply need to measure the length and width and multiply the two measurements. Convert inches to feet before multiplying to get square feet. Add that measurement to the square footage results from step 3.

Step 5: Include Overage for Waste

Experts recommend that you order 10 percent more carpeting than your measurements indicate to account for waste that normally occurs during the carpet installation process. There may be waste because carpet comes in rolls that are 12 feet or 15 feet wide and those widths may not perfectly match the layout of your project.


If your stairs are irregularly shaped, it’s best to have a carpeting professional measure and calculate stair carpet needs.