Square Footage Calculator

Find a rectangle area in square feet and its material cost.

Seven length units, five area units and 20 currencies with live exchange rates.

Updated October 19, 2026

CreatorFrank Zhao

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Overview

Square footage is the area of a surface measured in square feet. This calculator turns a rectangle you measured into its total area, and then turns that area into a material cost when you supply a price. You can also work in the opposite direction: start from an area you already know and recover a side length, the number of identical pieces, or the price per square foot.

The four questions it answers

How many square feet are in one rectangle, or in several identical ones?
What is the missing width, length or quantity when the area is already known?
What will flooring, paint, sod or sheeting cost at a given price per area?
What price per square foot does a total asking price imply?

It is useful whenever a surface is rectangular and you need to buy, rent or compare it: flooring and carpet, tiles, paint, wall panels, sod, mulch, roofing sheets, or the listed floor area of a property. Lengths and areas can be entered in metric or imperial units, and the price can be quoted in any of 20 currencies.

How to use this calculator

Fill in the boxes you know and leave the rest empty. The calculator fills the remaining box once it has enough information, so you do not need to enter the same measurement in two places.

Choose the width and length units

The two boxes have independent unit menus, so a room measured partly in metres and partly in feet is no problem. If your tape shows feet plus inches, select feet / inches and enter the two parts separately.

Enter one rectangle

Type the width and the length of a single rectangular surface. For a floor, measure at the points where the room is widest and longest rather than along one wall only.

Set the quantity if the rectangles repeat

Quantity multiplies one rectangle. Leave it at 1 for a single room, and raise it only when several rectangles share exactly the same width and length.

Read the area, or type it in instead

The Area box shows the total for all the rectangles. If the area is the value you already know, type it there and the calculator will solve whichever of width, length or quantity is still missing.

Add the price if you need a cost

In the cost section, choose the currency and the area denominator of the price (per square foot, square meter or square yard), then enter the price. Choose the currency you want the total shown in; it can differ from the price currency.

A complete example: two identical rooms

Each room is 12 ft by 10 ft, there are two of them, and the carpet is priced at $\$3.25$ per square foot, with the price set to US dollars per square foot.

A = N \times L \times W

A = 2 \times 12\ \mathrm{ft} \times 10\ \mathrm{ft}

= 240\ \mathrm{ft}^2

C = A \times P

= 240\ \mathrm{ft}^2 \times \$3.25/\mathrm{ft}^2

= \$780

The area covers both rooms; the price is per square foot, not per room. The total is a material estimate before any cutting allowance, tax, delivery or installation charge.

How the calculation works

The core is a product. Multiplying the quantity by the two sides of one rectangle gives the total area; multiplying that area by the price per unit area gives the material cost. All the unit work happens before those two multiplications, which is what lets a width in feet and a length in metres behave correctly.

A = N \times L \times W

C = P \times A

$A$ is the total area, stored in square metres.
$N$ is the quantity, $L$ the length and $W$ the width of one rectangle.
$P$ is the price per unit area and $C$ the total cost.

Lengths and areas are converted first

Both sides of the rectangle are converted to metres before they multiply. The factors are exact definitions rather than rounded table values: one inch is 2.54 cm by definition, so one foot is 0.3048 m and one yard is 0.9144 m.

1\ \mathrm{in} = 0.0254\ \mathrm{m}

1\ \mathrm{ft} = 0.3048\ \mathrm{m}

1\ \mathrm{yd} = 0.9144\ \mathrm{m}

1\ \mathrm{cm} = 0.01\ \mathrm{m}

Area units are the squares of those definitions, so no separate approximation is involved:

1\ \mathrm{ft}^2 = 0.09290304\ \mathrm{m}^2

1\ \mathrm{in}^2 = 0.00064516\ \mathrm{m}^2

1\ \mathrm{yd}^2 = 0.83612736\ \mathrm{m}^2

A composite entry simply adds its parts. Five feet ten inches is $5 \times 0.3048 + 10 \times 0.0254 = 1.778\ \mathrm{m}$ , and three metres twenty-five centimetres is $3 + 0.25 = 3.25\ \mathrm{m}$ .

The price is normalised, then converted back

A price quoted per square foot is really a price per 0.09290304 m². The calculator converts it to a price per square metre and from its currency into a single reference currency, multiplies by the area, and finally converts the total into whichever display currency you selected. The area denominator of the price and the area unit used for the result are independent choices.

P_{\mathrm{base}} = \frac{P_{\mathrm{entered}}}{r_{\mathrm{currency}} \times f_{\mathrm{price\ area}}}

C_{\mathrm{total}} = P_{\mathrm{base}} \times A

C_{\mathrm{display}} = C_{\mathrm{total}} \times r_{\mathrm{display}}

Here $r$ is how many units of a currency one US dollar buys, and $f$ is the number of square metres in the price denominator. Those rates are daily reference values, not the rate a bank or a supplier will necessarily give you.

Any box can be the answer

The two products are solved in both directions, so the same six boxes cover all the practical questions. If you know an area and one side, the other side follows; if you know a total and a price, the area follows; if you know a total and the area, the price follows.

N = \frac{A}{L\,W}

L = \frac{A}{N\,W}

W = \frac{A}{N\,L}

P = \frac{C}{A}

A = \frac{C}{P}

When a newly entered value completes the calculation, one of the boxes you filled earlier is recalculated so that the set stays consistent. That is why a value can move in a box you were not editing. If you need to keep a particular number, note it before you enter a value that conflicts with it, or clear the box you no longer need.

Worked examples

Sod for a rectangular yard

A back garden measures 30 ft by 45 ft. With the quantity left at 1, the area is $30 \times 45 = 1{,}350\ \mathrm{ft}^2$ . That is the measured surface, not the amount to order: sod is sold in rolls with fixed coverage and needs an allowance for cuts.

To turn the same area into rolls and a delivered price, continue with the Sod Calculator, which adds a waste factor and the price per roll.

One side missing from a recorded area

A note from a previous survey says a room has 850 ft² of floor and that one wall is 25 ft long. Enter 850 in Area, 25 in Length and leave Width empty. The result is $850 \div (1 \times 25) = 34\ \mathrm{ft}$ , so the other wall is 34 ft.

This is handy when you are buying a rug or a roll of flooring and only an old floor plan gives you the area and one dimension.

Comparing two listings by price per square foot

Set the price currency to US dollars and the denominator to square feet. Enter a listing's floor area in Area, its asking price in Total cost, and clear Unit price: the price per square foot is calculated for you.

Listing	Area	Asking price	Price / ft²
A	1,200 ft²	$240,000	$200
B	950 ft²	$199,500	$210

Listing A is cheaper per square foot even though it costs more overall. That does not make it the better home: condition, location and what each listing includes still matter, and listed areas are not always measured the same way. Use the number to start a like-for-like comparison, not to finish it.

Measurement tips

Quantity multiplies one rectangle

The area equation is $A = N \times L \times W$ , so Quantity multiplies the dimensions. If you already have the total area of several different rooms, leave Quantity at 1 and enter that total in Area instead; otherwise the same surface is counted twice.

Break odd shapes into rectangles

An L-shaped room is two rectangles, not one. Measure each piece, calculate its area, then add the results yourself. The same approach works for a bay window, a closet alcove or a floor with a chimney breast.

Measure the room, not the furniture

Take the width and length at more than one point: older walls are rarely perfectly parallel. For a purchase, it is safer to measure the widest and longest clear span and then decide how much cutting allowance the installer recommends.

Area is not a volume

Mulch, gravel and soil are sold by volume, which also depends on the depth you spread. If the next step is a garden bed rather than a flat covering, the Mulch Calculator turns an area and a depth into cubic yards or bags.

The calculator returns the measured area only. It does not add a waste allowance, deduct doors or windows, or include overlap, pattern matching, tax, delivery or labour. Ask the supplier or installer what allowance their material needs, then add it to your order.

Frequently asked questions

Why did a box I had already filled change?

The six boxes describe two connected equations rather than independent records. When a new value completes the set, the calculator recalculates one of the earlier boxes so the result stays consistent instead of holding a contradiction. If a particular number must not change, note it first, or clear the box whose value you no longer need.

Should I enter the area of one room or all of them?

The Area box represents the total of the rectangles described by Width, Length and Quantity. For identical rooms, enter one room's dimensions and set Quantity to the number of rooms. For rooms of different sizes, either calculate each one separately and add the results, or leave Quantity at 1 and type the combined area directly.

Can I find the price per square foot from a total price?

Yes. Leave Unit price empty, enter the known area in Area and the total in Total cost, and the price is calculated. Make sure the price denominator is the unit you want: square foot gives a price per square foot, while square meter or square yard gives the price on that basis.

Limitations and assumptions

Rectangles only. A room that is not a rectangle has to be split into rectangular pieces and the pieces added together.
No deductions. Doors, windows, fireplaces and fixed obstructions are not subtracted. For a large opening, calculate the wall without it or subtract the opening yourself.
Measured area, not a buying quantity. Cutting waste, overlap, pattern repeat, and material sold in fixed packs are outside the calculation.
Money is an estimate. Exchange rates are daily reference values. Taxes, delivery, installation and the supplier's own rounding can all change the final invoice.
The measurement sets the limit. The unit conversions are exact, but a tape reading is not. For a large or expensive order, confirm the quantities with your supplier or installer before committing.

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