Square footage:
measure a room, flat or plot

What square footage is and how to calculate it

Square footage is the area of a floor, room or plot, expressed in square feet. One square foot is a square that measures 1 foot on every side, so a room that is 10 feet by 10 feet holds 100 of them.

You meet the figure in property listings, rent quotes, flooring and tile estimates, paint coverage and air-conditioner sizing. Each of those is only as reliable as the measurement behind it.

The unit is a square, not a length. A room that is 12 feet long is not "12 square feet"; the number only means something once the width is multiplied in. Two rooms with the same perimeter can have very different square footage, which is why a long, narrow room feels smaller than a squarer one with the same wall length.

1. 1Measure length and width wall to wall at floor level, not along the skirting top or over furniture.
2. 2If you measured in feet and inches, turn the inches into a fraction of a foot by dividing by 12.
3. 3Multiply length by width.
4. 4For an L-shaped or irregular room, split it into rectangles, work out each one and add the results.

Example: an L-shaped living room

Feet and inches need one extra step. A wall of 11 ft 6 in is 11.5 ft, because 6 ÷ 12 = 0.5. A room measuring 11 ft 6 in by 9 ft 3 in is 11.5 × 9.25 ≈ 106.4 sq ft.

Round the final figure to the nearest whole square foot when you quote it. A tape measure is only good to about an inch, so decimals add false precision, and a lender, buyer or fitter will not rely on them.

A useful habit is to draw the plan, mark each side, and total the rectangles twice by different routes. If the two totals disagree by more than a few square feet, one measurement is wrong and it is cheaper to find it now than after the tiles arrive.

Triangles, circles and plots

Not every floor is a rectangle. A triangular corner or a round rug follows its own area rule, and you add or subtract it from the main rectangle.

• Triangle: ½ × base × height. A corner of 4 ft by 3 ft is ½ × 4 × 3 = 6 sq ft.
• Circle: π × radius². A round rug 8 ft across has a radius of 4 ft, so its area is π × 16 ≈ 50.3 sq ft.
• Plot in square yards: divide square feet by 9. A 30 ft × 40 ft plot is 1,200 sq ft, or about 133.3 sq yd.
• Acre: one acre is 43,560 sq ft, so a 5,000 sq ft plot is about 0.115 acre.

Measure the height of a triangle at a right angle to its base, not along the sloping side. This is the most common error when a room has an angled wall.

Convert square metres to square feet

Plans and brochures are often in metres. Because 1 ft is exactly 0.3048 m, one square metre equals about 10.764 square feet, and one square foot equals 0.0929 square metres.

Carpet, built-up and super built-up area

Two flats can both be "1,200 sq ft" and be very different homes. Carpet area is generally the usable floor inside the walls. Built-up area adds wall thickness and sometimes balconies. Super built-up area adds a share of common spaces such as lobbies and lifts.

Definitions and loading percentages vary by builder, city and agreement, so ask which area a quote uses and read the sale document.

• Which of the three areas does the quoted price per sq ft apply to?
• Are balconies, terraces and parking counted, and at what share?
• What percentage is added for common areas?
• Is the figure written in the agreement the same as the one in the brochure?

Using square footage for flooring and price per sq ft

Flooring needs an allowance for cuts and breakage. A common allowance is 5–10%, and more for diagonal layouts, so confirm the figure with your fitter. For the 222 sq ft living room, adding 10% gives 222 × 1.10 = 244.2 sq ft to order.

At an assumed material rate of ₹90 per sq ft, that is about ₹21,978 before labour. Price per sq ft works the other way round: ₹75,00,000 ÷ 1,250 sq ft = ₹6,000 per sq ft.

Rent follows the same logic. A flat let at ₹36,000 a month with 900 sq ft of carpet area costs ₹40 per sq ft per month. Divide before you compare, because a cheaper rent on a smaller flat can still be the dearer deal.

Mistakes that distort square footage

• Multiplying a side in feet by a side in metres or inches without converting first.
• Reading 11 ft 6 in as 11.6 ft. It is 11.5 ft.
• Counting a staircase, shaft or pillar block as usable floor.
• Comparing a rate per sq ft on carpet area with one on super built-up area.
• Ordering flooring with no wastage allowance.
• Measuring once. Walls are rarely perfectly square, so measure both ends of each side and use the larger figure when buying material.

Use the rectangle area calculator on this page for a single room, then the flooring cost calculator to turn the total into a budget. If you are comparing a flat's area with a rent or a loan, the same figure feeds the price per sq ft that every comparison starts from.