OneTripDIY

Square Footage Calculator

Enter the length and width and get the square footage. Measure in feet, inches, yards or meters — it converts for you — and add a section for each rectangle if the space is not a plain box.

By The OneTripDIY Team · Updated

Measure the space

Not a plain rectangle? Add a section for each part and we'll total them.

%

Optional. 10% is the usual allowance when the number is a material order.

Both boxes in the same unit. Mixed feet and inches? Enter 10 ft 6 in as 10.5 ft.

Square footage —
Area before extra — sq ft
Square yards — sq yd
Square meters — sq m
Acres — acres
Perimeter (all sections) — linear ft

Estimates only. Check against your supplier's stated coverage before you buy.

Take this list to the store

We'll email the quantities above, what you typed in, and a link that reopens this calculator already filled in — so you can adjust it on your phone in the aisle.

We send the list you asked for. Anything else only if you tick the box, and you can unsubscribe in one click. What we do with it.

An L-shaped room is two rectanglesSplit an odd shape into rectangles, work out each one, and add them together.AB20 × 15 ft = 300 sq ft12 × 7.5 ft = 90 sq ftA + B = 390 sq ft

How to work it out

  1. Measure length and width

    Measure the two sides of the space at floor level, wall to wall. Keep the tape flat and straight, and take the longest dimension in each direction. Both boxes must be in the same unit — set which one above.

  2. Split odd shapes into rectangles

    An L-shaped room is two rectangles, and a room with a bay is a rectangle plus a small one. Press “Add another section” for each piece; the sections are added together for you.

  3. Round up, not down

    If a wall is 12 ft 4 in, enter 12.33 rather than 12. Under-measuring is what sends people back to the store, and a few extra square feet costs less than a second trip.

  4. Add extra if you are buying material

    Square footage on its own needs no allowance. The moment it turns into an order — flooring, tile, sod — add 10%, or 15% for diagonal and herringbone layouts.

Square footage of common room sizes

Length × width, with no allowance added.

Room sizeSquare feetSquare yardsSquare meters
8 × 10 ft80 sq ft8.9 sq yd7.4 sq m
10 × 10 ft100 sq ft11.1 sq yd9.3 sq m
10 × 12 ft120 sq ft13.3 sq yd11.1 sq m
12 × 12 ft144 sq ft16.0 sq yd13.4 sq m
12 × 14 ft168 sq ft18.7 sq yd15.6 sq m
12 × 16 ft192 sq ft21.3 sq yd17.8 sq m
14 × 16 ft224 sq ft24.9 sq yd20.8 sq m
16 × 20 ft320 sq ft35.6 sq yd29.7 sq m
20 × 24 ft480 sq ft53.3 sq yd44.6 sq m

Converting square feet

The four conversions people look up most.

FromToDo this
Square feetSquare yardsdivide by 9
Square feetSquare metersdivide by 10.764
Square feetAcresdivide by 43,560
Square inchesSquare feetdivide by 144

How to measure square footage

Square footage is length times width, with both measured in feet. A room 12 ft by 14 ft is 168 square feet. That is the whole method for a rectangle, and most rooms are rectangles.

Measure at floor level rather than at waist height, and measure to the wall surface rather than to the baseboard. Where a wall is not straight, take the longest measurement — you cannot order material for the narrow part of a room and hope.

L-shaped rooms and odd corners

Every irregular space is a set of rectangles. Draw the room roughly on paper, cut it into rectangles with straight lines, and measure each one. Add a section here for each rectangle and they are totalled for you.

A triangle is half its base times its height. A circle is 3.1416 times the radius squared. A bay window is close enough to a half-circle or a trapezoid that either will serve for a material order.

Square footage of a whole house

For your own planning, measure each room and add them up. For anything official — a listing, an appraisal, a tax assessment — the US standard is ANSI Z765, which measures from the outside faces of exterior walls, counts only finished space with a ceiling above 7 ft, and leaves out garages, unfinished basements and open stairwells.

That is why a listing figure and the sum of your room measurements never agree: the listing includes wall thickness and hallways, and yours does not.

When to add extra

The square footage itself is exact. What you buy is not.

  • Flooring, tile, carpet: add 10% for offcuts, 15% for diagonal or herringbone layouts.
  • Paint: no allowance needed — buy by the can and the rounding covers you.
  • Sod and turf: 5–10%, more on a curved lawn.
  • Anything with a pattern repeat: follow the repeat, not a percentage.

How this is worked out

No black box — here is the arithmetic the calculator runs, so you can check it against your own numbers.

  1. area of one section = length × width The definition of area for a rectangle.
  2. total = sum of every section An L-shape or a bay is two or more rectangles.
  3. × (unit to feet)² Inches, yards and meters are converted before the area is worked out, and a squared measurement takes the conversion twice.
  4. × (1 + extra %) Only when you set an allowance for offcuts.
  5. perimeter = 2 × (length + width) per section The linear feet for baseboard, trim or edging.

Common questions

How do you calculate square footage?

Multiply length by width, both in feet. A 12 ft by 14 ft room is 168 square feet. If the space is not a rectangle, split it into rectangles, work out each, and add them together.

How many square feet is a 10x10 room?

100 square feet. That is 11.1 square yards, or 9.3 square meters.

How do I convert square feet to square meters?

Divide by 10.764. So 500 sq ft is 46.5 sq m. To go the other way, multiply square meters by 10.764.

How many square feet are in an acre?

43,560 square feet. A square acre is about 209 ft on each side.

How do I work out square footage from inches?

Either set the unit above to inches and enter the inch measurements, or divide square inches by 144 yourself. A 30 in by 60 in countertop is 1,800 square inches, which is 12.5 square feet.

Do I measure the floor or the walls?

It depends what you are buying. Flooring, tile and carpet need floor area, which is length times width. Paint, drywall and wallpaper need wall area, which is the perimeter times the ceiling height — the perimeter is shown above, and the paint calculator does the rest.

Does square footage include closets and hallways?

For a material order, include any floor you are covering, closets included. For a listing figure under ANSI Z765, finished hallways and closets count, but garages, unfinished basements and anything under a 7 ft ceiling do not.

How much extra should I order?

10% for most flooring and tile, 15% for diagonal or herringbone patterns, 5–10% for sod. Set it in the “Add extra” box and the total above includes it.

Where these figures come from

Every figure below is traceable. How we check the numbers explains how they are verified, and the coverage reference collects them all in one place.

  • NIST Special Publication 811 — the exact foot-to-meter conversion used for the metric figures
  • ANSI Z765 Square Footage Method for Single-Family Residences — what counts as finished square footage in a listing or appraisal
  • Flooring manufacturer installation guides — the waste allowances quoted for straight and diagonal layouts

Think a number here is wrong? Tell us — we check every report, correct the page, and date the change. Last checked September 27, 2026.