Stair Carpet Calculator: Estimate Carpet for Stairs

What Is a Stair Carpet Calculator?

A stair carpet calculator works out how much carpet is needed to cover a staircase. It uses the number of stairs, the width of each stair, the tread depth, the riser height, and an overlap allowance for the front edge of each step. The result is given in square meters or square feet.

Carpeting a staircase is not the same as carpeting a flat floor. Each step has a horizontal surface (the tread) and a vertical surface (the riser). Carpet must cover both, plus a small extra strip that wraps around the front edge of the step, called the nose. A calculator that skips any of these parts will underestimate the material needed.

Key Measurements

• Tread: the horizontal part of a step, where a foot lands.
• Riser: the vertical face between one step and the next.
• Width: the distance across a stair, from one side to the other.
• Overlap: extra carpet added to the tread-and-riser length so the carpet can wrap over the stair nose. This stops the edge from pulling back with wear.
• Number of stairs: the count of individual steps. Landings, the flat platforms between flights, are not steps and are measured separately.

Stair Carpet Formula

The area needed for one stair is its width multiplied by the combined length of tread, riser, and overlap. Multiplying by the number of stairs gives the total area:

Total area = Number of stairs × [Width × (Tread depth + Riser height + Overlap)]

For metric input, the result is worked out in square centimeters first, then divided by 10,000 to convert to square meters. For imperial input, it is worked out in square inches first, then divided by 144 to convert to square feet.

Switching between metric and imperial does not change the measurement itself: the calculator converts using the exact factor 1 inch = 2.54 centimeters, so a value entered in one unit and converted to the other represents the same physical length.

Example: Calculating Carpet for a Staircase

Consider a staircase with these measurements:

• Number of stairs: 12
• Stair width: 90 cm
• Tread depth: 25 cm
• Riser height: 18 cm
• Overlap: 5 cm

Step 1. Add the tread, riser, and overlap: 25 + 18 + 5 = 48 cm.

Step 2. Multiply by the width: 90 × 48 = 4,320 cm² per stair.

Step 3. Multiply by the number of stairs: 12 × 4,320 = 51,840 cm².

Step 4. Convert to square meters: 51,840 ÷ 10,000 = 5.18 m².

The staircase needs 5.18 m² of carpet by this formula. Because carpet is usually sold in fixed widths and cut in straight sections, installers commonly buy some extra material to allow for cutting waste; the exact amount depends on the stair shape and how the carpet is cut.

How to Measure a Staircase for Carpet

1. Count the stairs. Walk the full flight and count each step. Do not count landings.
2. Measure the width. Measure straight across the stair. If stairs vary in width, use the widest one so the order covers every step.
3. Measure the tread depth. Measure from the back of the tread, where it meets the riser above, forward to the front edge.
4. Measure the riser height. Measure from the top of one tread straight up to the top of the next tread.
5. Choose an overlap. A small allowance, commonly a few centimeters, lets the carpet wrap around the stair nose.
6. Enter the values and choose a unit system. The calculator returns the total area in square meters or square feet.

Landings are flat rectangles. Their area is length times width, calculated separately and added to the stair total for a full material estimate.

Stair Shapes and Carpet Waste

The formula above assumes a straight run of stairs with a constant width, tread, and riser. Other layouts need adjustment:

• L-shaped or U-shaped stairs can be measured as separate straight sections, then added together.
• Winder stairs, where steps are wedge-shaped at a turn, are usually measured along a walking line rather than at the narrow inside edge.
• Spiral and curved stairs have a tread width that changes across the step, so a single width measurement is only an approximation. Cutting carpet to fit a curve also produces more offcuts than cutting for a straight run.

Because curved and irregular stairs waste more material when cut, installers typically order a larger safety margin for them than for a straight staircase.

Frequently Asked Questions

How much carpet is needed for a 12-step staircase?

For stairs 90 cm wide with a 25 cm tread, an 18 cm riser, and a 5 cm overlap, the formula gives 5.18 m² (about 55.8 ft²). Actual staircases vary, so measurements should be taken individually rather than assumed.

What is the formula for stair carpet?

Total area equals the number of stairs multiplied by the width, multiplied by the sum of the tread depth, riser height, and overlap. The result is converted from square centimeters to square meters, or from square inches to square feet.

Why does the formula include an overlap, not just tread and riser?

The overlap accounts for the carpet that wraps around the front edge, or nose, of each step. Without it, the carpet would end flush with the edge and could pull loose from the tread with regular foot traffic.

Does this calculator include landings?

No. It calculates area for individual stairs only. A landing is a flat surface, so its area is its length multiplied by its width, added separately to the stair total.

Why doesn't the calculated area match what I need to buy?

The formula gives the exact surface area of the stairs. Carpet is sold and cut in fixed widths, and any cuts, especially around curves or corners, create offcuts that cannot be reused elsewhere. For that reason, the amount purchased is usually higher than the calculated area, with the margin depending on the stair shape.

Does switching between metric and imperial change the result?

No. The calculator converts length using the exact factor 1 inch = 2.54 centimeters before recalculating area, so the physical measurement stays the same regardless of which unit system is selected.