Square Footage Calculator
Last updated: 28 June 2026
Reviewed by Gavin Meiring, Lead research and primary author · Doctoral Candidate (Corporate Governance) · Research and drafting assisted by AI
- The average new US home in 2022 was 2,299 sq ft — over twice the average in 1950 (983 sq ft), despite families being smaller. Average UK new-builds are around 818 sq ft.
- Tokyo apartment listings sometimes advertise spaces in 'tatami mat units'. A tatami mat is approximately 1.62 m² (17.4 sq ft). A 6-tatami room is about 9.7 m².
- Real estate agents measure floor area differently in different countries. In the UK, floor area excludes walls. In France (Loi Carrez), it excludes areas under 1.8m ceiling height.
Square Footage Calculator
A square footage calculator computes the area of a room, floor, or outdoor space in square feet, square metres, or square yards. It is used by homeowners, contractors, estate agents, and interior designers to measure flooring, tiling, paint coverage, carpet, and land area for planning and purchasing purposes.
How to Use the Square Footage Calculator
- Select the shape of the space: rectangle, square, triangle, circle, or L-shape.
- Enter the dimensions in your preferred unit: feet, inches, metres, or yards.
- For irregular rooms, divide the space into simple shapes, calculate each separately, and add the results.
- Click "Calculate" to see the total area.
- For material purchases, enter the coverage per unit (e.g., tiles per box or paint per litre) to get a quantity estimate. Always add 10% for cuts and wastage.
The Formula
The formula depends on the shape:
Rectangle or Square: Area = Length x Width
Triangle: Area = 0.5 x Base x Height
Circle: Area = Pi x Radius² (where Pi = 3.14159 and Radius = Diameter / 2)
Trapezoid: Area = 0.5 x (Side A + Side B) x Height
L-shaped room: Divide into two rectangles, calculate each, and sum: Area = (L1 x W1) + (L2 x W2)
Unit conversions:
- 1 square metre = 10.764 square feet
- 1 square yard = 9 square feet
- 1 square foot = 144 square inches
Real-World Example
You want to tile a rectangular kitchen floor measuring 14 feet long and 11 feet wide, with a small rectangular alcove that is 3 feet by 4 feet.
Main room area: 14 x 11 = 154 sq ft Alcove area: 3 x 4 = 12 sq ft Total area: 154 + 12 = 166 sq ft
Adding 10% for tile cuts and wastage: 166 x 1.10 = 182.6 sq ft
The chosen tiles cover 15 sq ft per box (typically 6 tiles per box). Number of boxes needed: 182.6 / 15 = 12.2 boxes, rounded up to 13 boxes.
You should purchase 13 boxes to cover the floor with enough material for wastage, cuts around the edges, and a few spares for future repairs.
Room by room
A four-room flat measured in metres, converted to square feet at 10.7639 square feet to the square metre. The conversion factor is exact rather than approximate. The international foot is defined as 0.3048 metres, so one square foot is 0.3048 squared, which is 0.09290304 square metres, and one square metre is 1 divided by that figure, which is 10.7639104 square feet.
| Room | Size | Square metres | Square feet |
|---|---|---|---|
| Living room | 5.4 m by 3.8 m | 20.52 | 220.9 |
| Main bedroom | 4.2 m by 3.6 m | 15.12 | 162.8 |
| Second bedroom | 3.0 m by 3.0 m | 9.00 | 96.9 |
| Kitchen | 3.6 m by 2.7 m | 9.72 | 104.6 |
| Total | 54.36 | 585.1 |
The total is 54.36 square metres, which is 585.1 square feet, or 65.01 square yards. Carpet ordered with 10 percent wastage comes to 59.8 square metres, or 643.6 square feet.
The metric total and the imperial total are not independent figures. Every square metre is the same 10.7639 square feet, so a supplier quote in either unit should land within a rounding error of the other. When it does not, one of the inputs is wrong.
Feet and inches
Tape measures in the UK and the US are marked in feet and inches, and the calculator wants decimal feet. Six inches is 0.5 feet, three inches is 0.25 feet, and nine inches is 0.75 feet. Dividing the inches by 12 converts them correctly.
The common error is to divide by 10 instead, and the table shows what that costs on a room measured as 10 feet wide.
| Measurement | Correct decimal feet | Dividing by 10 | Area at 10 ft wide | Area with the error |
|---|---|---|---|---|
| 12 ft 6 in | 12.50 | 12.60 | 125.00 sq ft | 126.00 sq ft |
| 10 ft 3 in | 10.25 | 10.30 | 102.50 sq ft | 103.00 sq ft |
| 14 ft 9 in | 14.75 | 14.90 | 147.50 sq ft | 149.00 sq ft |
A room 12 ft 6 in by 14 ft 9 in measures 181.25 square feet when both sides are converted correctly. Dividing by 10 on both sides gives 12.6 by 14.9, which is 187.74 square feet. That is 6.49 square feet too high, and it is enough to order the wrong number of tile boxes.
Common measurement errors
Three errors account for most wrong square footage figures.
Measuring to the skirting board rather than to the wall adds the thickness of the board along two sides. Pencil round moulding is typically about 15 mm thick, and on a small room that adds roughly 0.1 square metres to the total.
Reading a floor plan without checking the scale is the second. A plan drawn at 1:50 and a plan drawn at 1:100 look alike on paper and describe very different rooms. Use the printed dimensions where the plan carries them.
Rounding each room to the nearest square foot before adding is the third. Round once, at the end, on the total. Four rooms each rounded up by half a square foot overstate the floor by two square feet.
Floor plan scales
A scale of 1:50 means one unit on the drawing equals 50 of the same unit in the room. A 100 mm line on a 1:50 plan is 5,000 mm on site, which is 5 metres. The same line on a 1:100 plan is 10 metres.
For area the scale factor applies twice. A shape covering 20 square centimetres on a 1:50 plan covers 20 multiplied by 50 multiplied by 50, which is 50,000 square centimetres, or 5 square metres. On a 1:100 plan the same 20 square centimetres becomes 20 square metres, four times as much.
Wastage by layout
The 10 percent allowance in the worked example above suits a straight lay in a rectangular room. The pattern changes it.
| Layout | Allowance | Square metres to order | Cost of the allowance at £12 per m² |
|---|---|---|---|
| Straight lay | 10% | 59.80 | £65.23 |
| Diagonal lay | 15% | 62.51 | £97.85 |
| Herringbone | 15% | 62.51 | £97.85 |
| Many cuts and angles | 20% | 65.23 | £130.46 |
The allowance applies to the area, not to the number of boxes, so round up after the allowance rather than before. On the 54.36 square metre total, straight lay needs 59.80 square metres and a 15 percent allowance needs 62.51 square metres, a difference of 2.71 square metres of material.
Painting a room
Wall area is a square footage problem with a subtraction. A room 4.2 metres by 3.6 metres with a 2.4 metre ceiling has a wall perimeter of 2 multiplied by (4.2 plus 3.6), which is 15.6 metres. Wall area is 15.6 multiplied by 2.4, which is 37.44 square metres.
Subtract a door of 0.9 by 2.1 metres, which is 1.89 square metres, and a window of 1.2 by 1.2 metres, which is 1.44 square metres. The paintable area is 37.44 minus 1.89 minus 1.44, which is 34.11 square metres.
Two coats need 68.22 square metres of coverage. At 12 square metres per litre that is 5.7 litres, so one 5 litre tin plus one 1 litre tin. Buying two 5 litre tins would leave 4.3 litres unused.
Converting Between Units
Many materials are sold in metric units while older building plans in the UK and US may use imperial measurements. Here are useful conversions:
- 1 square metre = 10.764 square feet
- 100 square feet = 9.29 square metres
- 1 square yard = 0.836 square metres
- 1 acre = 43,560 square feet = 4,047 square metres = 0.405 hectares
- 1 hectare = 10,000 square metres = 107,639 square feet
For estate agent listings: UK property floor areas are typically given in both square metres and square feet. A 50 m² flat is approximately 538 sq ft. A 100 m² house is approximately 1,076 sq ft. Knowing how to convert between these helps when comparing properties listed in different formats.
Frequently Asked Questions
How do I measure an irregular-shaped room? Divide the room into simple geometric shapes such as rectangles, triangles, or L-shapes. Measure each section separately, calculate the area of each, and then sum the results. For very complex shapes, you can sketch a floor plan on graph paper and count the grid squares. A digital floor plan app can also help with irregular rooms.
Should I include the area under furniture when calculating flooring? Yes. Flooring materials are measured for the entire room area, including under fitted furniture, because the flooring is laid before furniture is placed. The exception is if you are replacing flooring around permanently fixed cabinetry (such as kitchen cupboards), in which case you can subtract those areas from your total.
How much extra material should I buy for wastage? The standard recommendation is 10% for straight-lay tile and flooring in rectangular rooms. For diagonal or herringbone patterns, add 15%. For rooms with many angles or cuts, add up to 20%. Always buy materials from the same production batch to ensure colour consistency; buying too little later may mean a different dye lot.
What is the difference between gross and net floor area? Gross floor area (GFA) includes the total area within the external walls, including walls, columns, and structural elements. Net floor area (NFA) or net internal area (NIA) is the usable space only, excluding walls and service areas. Estate agents in the UK typically quote net internal area, while developers often quote gross floor area. For flooring estimates, use the net area of each room.
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