Carpet Calculator

Running out of flooring mid-room is the most avoidable mistake in a flooring job — and the fix is ten minutes with a tape measure before you order. This page does that measuring for carpet in a master bedroom in cut-pile carpet, with the estimate warning up front: the numbers here are estimates. Carton coverage, waste and prices vary by brand, product line and region, and the label on the product you buy governs. We use typical values from our material data — carpet cartons typically cover sold by the sq ft / sq yd off a roll, not by the box, and straight runs typically need 5–10% extra — and we show the result as a range, so you can order the high end and keep a spare box for future repairs.

How the calculation works

The calculator needs three inputs, and each one changes the answer. First, the area: length times width, minus anything that will not be floored, such as no fixed deduction. A room that measures 12 ft by 14 ft is 168 sq ft (15.6 sq m) before deductions. Measure each section separately if the room is L-shaped or has an alcove — one long measurement across an angled wall will overstate the area and waste your money, while one short measurement will leave you short. Second, the material: carpet is sold in cartons covering sold by the sq ft / sq yd off a roll, not by the box. The calculator uses a typical 0 sq ft per carton for carpet unless your carton label says otherwise, and the label wins whenever the two disagree. Third, the waste allowance: straight runs typically need 5–10% extra for end cuts, damaged planks and the stagger pattern. Diagonal layouts, herringbone patterns and rooms with many doorways need more — plan on the high end of the range, or above it, if your room has either.

The formula is short: flooring needed = (net area × (1 + waste %)) ÷ coverage per carton, rounded up to whole cartons. Always round up — cartons cannot be split, and a half-carton shortfall means a second order from a different dye lot. For carpet the formula is the same shape but the unit is different: carpet is sold by the sq ft or sq yd off a roll, not by the box, so the result is an area plus waste, and you should allow extra for pattern matching and seams. Note what the formula does not do: it does not assume a single coverage rate. If a retailer quotes one number for a carton, treat it as a starting point and check the label — the range is the honest figure.

Worked example: a master bedroom in cut-pile carpet

Here is the full arithmetic for a master bedroom in cut-pile carpet, a 12 ft by 14 ft room (3.7 m by 4.3 m).

Step 1 — gross area. 12 ft × 14 ft = 168 sq ft.

Step 2 — deduct what is not floored. Subtract 0 sq ft for no fixed deduction. Net area = 168 − 0 = 168 sq ft (15.6 sq m), which is 18.7 sq yd.

Step 3 — add waste. At 5% waste: 168 × 1.05 = 176.4 sq ft, or 19.6 sq yd. At 10% waste: 168 × 1.10 = 184.8 sq ft, or 20.5 sq yd. So you need to buy for 19.6–20.5 sq yd of carpet.

Step 4 — seams and pattern. Carpet comes off a roll, usually 12 ft (3.66 m) wide, so check how the roll width falls across your room: a 14 ft wide room may need a seam, and a patterned carpet needs extra length for pattern matching — typically a full pattern repeat per drop. If your carpet has a pattern, add that repeat length before you order, and ask the retailer to confirm the seam placement on the cutting plan.

Step 5 — underlay and extras. Underlayment or carpet pad is usually sold by the sq yd as well, so plan on the same 20.5 sq yd at the high end, plus tack strips around the perimeter and a threshold bar at each doorway. Keep an offcut of at least a few sq ft for future repairs — a matching patch is worth far more than the offcut costs to store.

Cost guidance

Costs on this page are ranges, labelled typical retail range — check the current shelf price before budgeting. No single national price is quoted, because carpet flooring prices vary by brand, product line, region and retailer, and a price that is right in one store can be wrong in the next. The way to budget is to multiply, not to guess: take the quantity from the worked example (19.6–20.5 sq yd), multiply it by the shelf price per sq yd on the exact product you have chosen, then add underlayment, trim, thresholds, adhesive if your product needs it, and the cost of any levelling or moisture barrier for the subfloor. For this job that means order 20.5 sq yd of carpet plus 20.5 sq yd of pad at the high end of the underlayment range, each priced from the shelf where you buy them.

Two cost traps catch first-time flooring buyers. The first is ordering the low end of the range and then paying a second delivery charge — or a higher per-carton price — for the one carton that finishes the job. The second is forgetting the extras: underlayment, skirting or quarter-round, thresholds and adhesive together are a meaningful share of a small job's material cost, and a subfloor that needs levelling can cost more than the flooring itself. Compare the total, not the per-carton price, and keep one unopened carton for future repairs; a matching dye lot is worth far more than the shelf price of that carton later. If you are hiring the work out, labour is usually quoted separately per sq ft and varies by region and by the complexity of the layout — a herringbone or diagonal floor costs more to lay than straight runs of the same area, so get the quote against the same layout you used for the material count.

Step by step: measure, calculate, order

1. Measure twice. Measure the room in feet at the longest and widest points, and measure each alcove, doorway and angle separately. Rooms are rarely perfect rectangles — measure every wall, sketch the shape on paper, and note the no fixed deduction so you can deduct it. Convert inches to decimal feet (6 in = 0.5 ft) before multiplying.

2. Choose the material and the direction. Pick the carpet product first, then decide which way the planks run — usually along the longest wall or toward the main light source. The direction sets where the cuts fall, and a run that ends in a sliver-width plank looks wrong, so dry-lay the first row in your head or on the floor before you order.

3. Use the calculator on this page. Enter the net area, the material (carpet), and the waste percentage for your layout. The tool returns a range — 19.6–20.5 sq yd for the example above — and you should plan on the high end. Check the carton label against the calculator's assumed per-sq-yd figure; if your carton covers less, the carton count goes up.

4. Order and check the delivery. Order order 20.5 sq yd for the example job, all from the same dye lot, and check the lot numbers on the cartons before the installer starts. Acclimatise the cartons in the room for the period the product label states — usually at least 48 hours — and keep them flat, dry and out of direct sun.

5. Before you start laying. Check the subfloor is flat, clean and dry, confirm the moisture reading against the product label, and make sure you have spacers, a tapping block, a pull bar and a spare carton within reach. Cutting the last plank to fit is normal; discovering you are a carton short with the floor half laid is not.

Frequently asked questions

How much carpet do I need for a room?

Measure length times width, add 5–10% for waste, and order by the sq yd. For the worked example on this page — 168 sq ft — the answer is 19.6–20.5 sq yd. Allow extra for pattern matching and seams, and keep an offcut for repairs.

How much carpet is in a box?

Typically about 0 sq ft per carton (sold by the sq ft / sq yd off a roll, not by the box) — but that is a typical value from our material data, not a promise. The carton label on the exact product you buy governs, and some lines pack more or fewer planks per carton. Always confirm the sq ft per carton on the label before you order.

How much waste should I add for carpet flooring?

Straight runs typically need 5–10% extra for end cuts, damaged planks and the stagger pattern. Diagonal layouts, herringbone patterns, rooms with many doorways and L-shaped rooms all need more — plan on the high end of the range, or above it, if your room has any of those. A bay window alone can add a full plank's worth of cuts.

Do I need underlayment under carpet?

It depends on the product and the subfloor. Many vinyl planks have attached underlay and need none, while laminate and engineered wood usually need a separate underlay for sound and moisture. One roll typically covers about 100–200 sq ft, so 168 sq ft needs about 1–2 rolls. Check the product label — using the wrong underlay can void the warranty.

Can I mix dye lots if I run short of carpet?

You can, but you should not plan to. Planks from different dye lots can differ slightly in shade, and the difference is most visible in daylight across a large floor. That is why this guide tells you to order the high end of the range up front and keep one spare carton — a matching spare is cheaper than relaying a visible patch later.

What is the most common mistake when ordering carpet flooring?

Ordering the exact net area with no waste allowance. Every real job has end cuts, a damaged plank or two, and at least one cut that goes wrong. The 5–10% waste range on this page exists for that reason — order the high end, and treat the spare carton as insurance, not waste.

Related calculators

Results are estimates — verify with the product label. Coverage, pack sizes, yields and prices vary by brand, product line, surface and region; the label on the product you buy governs. Cost figures are typical retail ranges — check the current shelf price before budgeting.