Carpet Calculator

How to use this carpet calculator

What this calculator does. It estimates the two-dimensional carpet area for a rectangle, circle, ellipse, regular pentagon, or regular hexagon, adds a user-selected cutting allowance, and multiplies the resulting purchase area by a material price. It is useful for early budgeting and quantity checks, but it does not design seam placement, enforce a retailer's roll width, choose a carpet grade, or quote installation labor. Area is expressed in square units; NIST's guide to area and square-meter measurement explains why linear dimensions must be converted consistently before they are multiplied.

When to use it. Use the estimate when comparing carpet materials sold by the square foot or square meter, setting a preliminary room-renovation budget, checking whether a supplier quantity includes enough cutting margin, or estimating a custom circular or regular-polygon rug. For irregular rooms, divide the floor into simpler shapes and calculate each portion separately, or obtain a professional measure when seams and roll direction matter.

How to calculate. The calculator opens with a complete demonstration: a 12 ft by 10 ft rectangle, a 10% allowance, and a price of $4.25 per square foot. Its example workbook is immediately available.

1. Choose Shape and Measurement unit. The dimension labels adapt to the selected geometry.
2. Replace the demonstration dimensions with your measurements. Use decimal points, not decimal commas, and enter positive finite values.
3. Set Cutting allowance. Ten percent is a general planning example, not a rule for every project.
4. Enter Price per square unit in U.S. dollars for the active area unit. Read the base area, allowance area, purchase area, and material cost.
5. Select Download Excel to create a current-state workbook. Reset clears the demonstration and calculated data; Excel export stays disabled until a complete valid state is entered again.

Input guide. Shape is required and selects the area formula. Rectangle uses Length × Width. Circle uses Radius² × π. Ellipse uses Semi-axis A × Semi-axis B × π; each axis value is a center-to-edge distance, not a full diameter. Regular pentagon and regular hexagon use one positive Side length. Measurement unit is required; switching between feet and meters converts existing dimensions and the price basis so the estimated cost remains essentially unchanged apart from display rounding. Length / Radius / Semi-axis A / Side is required, accepts a plain positive decimal such as 12, and controls area quadratically for circle and regular polygons but linearly for rectangle and ellipse. Width / Semi-axis B is required only for rectangle and ellipse; a value such as 10 is valid. Cutting allowance is required, accepts 0 – 100%, and increases purchase area and cost in direct proportion; typing “10%” is accepted, while a decimal comma such as “10,5” is rejected to avoid ambiguity. Price per square unit is required, accepts a nonnegative U.S.-dollar amount such as 4.25, and changes cost without changing area. Do not mix a square-meter price with foot dimensions unless you first switch the unit selector.

Output guide. Estimated carpet cost is the purchase area multiplied by the active unit price; it is a planning estimate, not a contractor quote. Base area is the exact geometric area implied by the entered dimensions. Allowance area is base area × allowance percentage. Purchase area is base plus allowance and is the quantity used for pricing. Price basis repeats the active unit rate. The summary pills show the same current shape, base area, allowance, and cost. The composition ring and table split the purchase quantity into measured carpet and allowance; their parts always add to the total. Zero allowance is valid and produces no second chart segment, while a zero price yields a $0.00 cost but still shows area.

Worked example. The startup rectangle has 12 ft × 10 ft = 120.00 sq ft of base area. A 10% allowance adds 12.00 sq ft, so the purchase area is 132.00 sq ft. At $4.25 per sq ft, the measured portion costs $510.00 and the allowance portion costs $51.00, producing the displayed material estimate of $561.00. These same typed values appear in the initial results, breakdown table, chart summary, and workbook.

Learn more. A sound quantity estimate should be paired with product and site checks. The U.S. EPA discusses environmental considerations when identifying greener carpet, and its remodeling guidance advises against carpet in locations with persistent moisture risk in home indoor-air-quality planning. For labeled fiber content and product comparison, consult the FTC's textile labeling guidance.