Stair Carpet Calculator: Area, Rolls and Cost Estimator
Enter your stair dimensions and this calculator works out the total carpet area, how many rolls or linear metres you need, and the estimated cost. It accounts for tread run, riser height, nosing overhang, landing depth, stair width, and a waste allowance. Switch between metric and imperial units, and the result updates instantly as you type.
Formula
Worked example
A standard 13-step staircase with a 10 in tread, 7.5 in riser, 1.5 in nosing, 36 in width, no landing and 10% waste: length per step = 10 + 7.5 + 1.5 = 19 in. Total linear length = 13 x 19 = 247 in = 20.58 ft. Net area = 20.58 x 3 = 61.75 sq ft. With 10% waste: 67.9 sq ft (7.55 sq yd, 6.31 sq m).
How to measure your stairs for carpet
Accurate measurement is the most important step in buying stair carpet. For each step you need three measurements:
- Tread depth: the horizontal surface you walk on, measured from the front nose to the riser below.
- Riser height: the vertical face between two treads. For open-riser (floating) stairs this is zero.
- Nosing overhang: how far the tread projects beyond the riser. Typical UK and US nosings are 1 to 1.5 inches (2.5 to 3.8 cm). Carpet must wrap under the nose to look neat and stay secure.
Measure the stair width at the narrowest point (often between banisters or walls). Use the same measurement for every step unless your staircase is shaped. For a landing at the top or bottom of the flight, measure its depth along the direction of travel and enter it in the landing field.
How the carpet area formula works
Each step needs carpet equal to: tread depth + riser height + nosing overhang. Multiply that by the number of steps and you get the total linear run. Add the landing depth if there is one. Then multiply by the stair width to get the net carpet area. Finally, apply a waste allowance (typically 10% for plain carpet, 15-20% for patterned or large-repeat designs that need pattern matching). The formula is:
Area = (steps × (tread + riser + nosing) + landing) × width × (1 + waste%)
Carpet is sold by the square foot, square yard, or square metre depending on your region. The calculator shows all three so you can use whichever unit your supplier quotes.
Waste allowance and pattern repeats
A 10% waste allowance is the standard minimum for a plain carpet with no directional pattern. Add extra for these cases:
- Patterned carpet: each step must start at the same point in the pattern repeat. A 25 cm repeat on a 10-step flight can waste a full repeat per step, adding 15-25% to your order.
- Winding or curved stairs: each step is a different width. Order extra and cut individually.
- Stair runners: the carpet is narrower than the full tread width. Runners are fitted with gripper rods, which also require separate ordering.
- Off-cuts for repairs: keeping a small remnant of the original carpet is useful for future patch repairs.
When in doubt, over-order slightly: running short of carpet mid-staircase and returning to a shop for more risks a dye-lot mismatch that will be visible once installed.
Carpet roll widths, cuts and economy
Most broadloom carpet comes on rolls 12 ft (3.66 m) or 15 ft (4.57 m) wide. A standard UK roll is 4 m or 5 m wide. If your stair width is under 12 ft, a single roll width can carpet the full stair with a lengthwise cut down the middle for a runner, or be used as full-width broadloom. Narrower staircases (under 3 ft or 90 cm) can often be cut economically from one roll width. Wider staircases may require seams, which adds material and installation cost. Discuss roll width with your supplier before ordering to minimise waste: choosing the right roll width for your stair width is often more important than the nominal price per yard.
Standard stair dimensions and carpet coverage guide
| Stair type | Tread depth | Riser height | Typical width | Carpet per step (approx.) |
|---|---|---|---|---|
| Standard US residential | 10-11 in | 7-7.75 in | 36-42 in | 1.5-2.2 sq ft |
| Compact US residential | 9-10 in | 7.75-8.25 in | 36 in | 1.3-1.8 sq ft |
| UK standard | 25-27 cm | 17-19 cm | 90-100 cm | 0.14-0.20 sq m |
| Open-riser/floating | 10-12 in | 0 in (open) | 36-48 in | 0.8-1.5 sq ft |
| Stair runner (not full) | 10-11 in | 7-7.75 in | 27-30 in (runner only) | 1.1-1.7 sq ft |
Typical residential stair dimensions per IRC and common UK building regulations.
Frequently asked questions
How much carpet do I need for 13 steps?
A typical 13-step US residential staircase (10 in tread, 7.5 in riser, 1.5 in nosing, 36 in wide) needs about 68 sq ft or 7.5 sq yd with a 10% waste allowance. Enter your exact measurements above to get a figure for your specific stairs.
Do I need to include the riser when measuring for carpet?
Yes, if you are carpeting the full staircase. Full-carpet installation covers both the tread (horizontal surface) and the riser (vertical face), so both measurements are added together for each step. If you want a stair runner that only covers the tread and not the riser, set the riser to zero and adjust your width to the runner width.
What is a nosing overhang and why does it matter?
The nosing is the edge of the tread that overhangs the riser below. Carpet must wrap around and under this nose so the edge is protected and the carpet stays tucked in. A typical overhang is 1 to 1.5 inches (2.5 to 3.8 cm). If you ignore the nosing in your calculation you will be short of carpet by about 1.5 in per step - on a 13-step staircase that is almost 20 in (half a metre) of carpet that you will be missing.
How much extra carpet should I order for a patterned staircase?
Order at least 15-20% extra for a patterned carpet, rather than the standard 10%. Each step must begin at the same point in the pattern repeat to look consistent. On a carpet with a 25 cm (10 in) repeat, you may waste up to a full repeat per step when cutting, which adds up quickly across a full flight. Ask your supplier for the pattern repeat measurement and factor it in before ordering.
What is a stair runner and how do I calculate carpet for it?
A stair runner is a strip of carpet narrower than the full stair width, fitted along the centre of each step and held in place with gripper rods or stair rods. To calculate runner carpet, enter the runner width (typically 24-30 in / 60-75 cm) as your stair width instead of the full stair width. The tread and riser measurements remain the same. You also need to add the gripper rod material separately.
How do I calculate carpet for a landing at the top of the stairs?
Measure the depth of the landing along the direction of travel (usually the same as the stair width direction) and enter it in the "Landing depth" field. The calculator adds this to the total linear length before computing the area. If your landing is wider than the staircase you may need a separate calculation for the extra landing width.
How many square yards of carpet do I need for stairs?
Divide your total square footage by 9 to convert to square yards. A typical 13-step staircase needs roughly 7-8 sq yd. Carpet is frequently sold in the US by the square yard, so the calculator shows sq yd alongside sq ft and sq m. Some suppliers also require you to specify a linear yardage based on a standard 12 ft roll width, which is a different measurement entirely.