Square footage calculator
Measure several rooms at once in feet, inches or metres, add a waste allowance and a cost per square foot, then export the list.
- Runs in your browser
- Nothing you enter is sent
- Free, no account
Area
252 sq ft
Area
48 sq ft
Measured area
300 sq ft
With 5% waste
315 sq ft
In square metres
29.26 m²
In square yards
35 sq yd
Estimated cost
$0.00
enter a price to see this
| Area | Shape | Dimensions | Sq ft |
|---|---|---|---|
| Living room | Rectangle | 18' 0" × 14' 0" | 252 |
| Hallway | Rectangle | 12' 0" × 4' 0" | 48 |
Formula and working
Area of each shape
Rectangle: length × width · Rectangle: length × width Living room: 18.00 × 14.00 ft = 252.00 sq ft Hallway: 12.00 × 4.00 ft = 48.00 sq ft = 300 sq ft total
Metric conversion
1 sq ft = 0.09290304 m² exactly (1 ft = 0.3048 m) 300.00 × 0.09290304 = 27.871 m²
Feet-and-inches entries such as 12′ 6″ are read exactly, and the conversion to metres uses the international foot of 0.3048 m, which is exact by definition.
Assumptions
- Measure the longest and widest points of each space, and split awkward rooms into two rectangles rather than trying to describe them with one shape.
- Waste allowance covers off-cuts, breakages and mistakes. Ten per cent is the usual figure; go to fifteen for diagonal layouts, herringbone patterns or a room with many angles.
- Quantities are always rounded up to whole units — cans, boxes and bags are not sold in fractions.
- Square footage is a plan area. It does not account for skirting, thresholds, or the direction a plank or tile will run.
- Nothing is uploaded. Saving is off by default and writes only to this browser, with a delete button next to the switch.
Multi-room, because one room is rarely the question
Almost every square-footage page online handles a single rectangle. Real jobs are a lounge plus a hallway plus a landing, or four rooms of flooring quoted as one order. Add a row per space here, mix shapes freely, and the total accumulates across all of them — with the whole list exportable as CSV, Excel or PDF to take to a merchant.
The formulas
| Shape | Area | Measure |
|---|---|---|
| Rectangle | length × width | the two longest perpendicular walls |
| Square | side² | one side |
| L-shape | (long × width) − (cut-out length × cut-out width) | the full rectangle, then the missing corner |
| Triangle | (base × height) ÷ 2 | height is perpendicular to the base, not a sloping side |
| Circle | π × (diameter ÷ 2)² | widest point across |
| Trapezoid | ((a + b) ÷ 2) × height | the two parallel sides and the distance between them |
For anything genuinely awkward, resist the temptation to find a clever shape. Split it into two rectangles and add a second row — it is faster, it is easier to check, and it is much harder to get wrong.
Feet, inches, metres — and feet-and-inches
Pick a unit once and it applies to every field. Beyond that, feet-and-inches notation is
understood in any field regardless of the selector: 12' 6", 12ft 6in
and 12'6 all read as 12.5 feet. Tape measures speak in feet and inches, so the
calculator should too.
Every result appears in square feet, square metres and square yards simultaneously. The conversion uses the international foot of exactly 0.3048 m, so one square foot is exactly 0.09290304 m² — no rounding error creeps in between the two systems.
Conversions worth knowing
| From | To | Multiply by |
|---|---|---|
| Square feet | Square metres | 0.092903 |
| Square metres | Square feet | 10.7639 |
| Square feet | Square yards | ÷ 9 |
| Square feet | Acres | ÷ 43,560 |
| Square metres | Hectares | ÷ 10,000 |
How to measure so the number is right
- Measure at the widest and longest points, wall face to wall face, not along the skirting.
- Take each dimension twice, at opposite ends of the room. Older buildings are rarely square, and a 3-inch discrepancy over 14 feet is normal.
- Include alcoves and bay windows as their own rows if you are buying material to cover them.
- Decide once whether doorways and thresholds are in or out, and be consistent across every room.
- Write the measurements down before you start typing. Re-measuring is cheap; a wrong order is not.
Waste allowance
The area you measure is never the quantity you buy. Off-cuts, breakages, pattern matching and the piece you cut backwards all consume material. Five to ten per cent covers most jobs; fifteen is sensible for diagonal layouts, long narrow rooms, or anywhere with a lot of doorways and angles. The allowance is applied to the net area before any cost is worked out.
Cost per square foot
The cost field multiplies the area-with-waste by whatever rate you enter — flooring, turf, insulation, rent, cleaning, a build estimate. It is deliberately generic, because "cost per square foot" is used for wildly different things and the arithmetic is identical for all of them. For material-specific quantities, the sibling calculators handle paint, tile, flooring and concrete with their own rules.
Property square footage is a different question
If you are measuring for a listing or a valuation, note that "gross internal area" definitions vary by country and by professional standard: some include stairwells, some exclude garages and unheated space, some measure to the internal wall face and others to the external. This page computes geometry honestly; which surfaces to include is a question for the standard you are working to.
Measure a whole house offline
There is no server behind this page, so it works fine in a basement with no signal. Nothing is uploaded, and your measurement list is only stored if you switch saving on — in this browser only, with a delete button beside the switch. The CSV, Excel and PDF exports are generated on your own device.
Questions
How do I calculate square footage?
Multiply length by width in feet. A 12 by 14 foot room is 168 square feet. Irregular spaces are easier as two rectangles than one complicated shape, and this page adds up as many rows as you need.
Can I measure in metres or inches?
Yes — pick the unit once and it applies to every field. Feet-and-inches notation such as 12' 6" is understood in any field regardless of the selector, and every total is shown in square feet, square metres and square yards.
How do I handle an L-shaped room?
Use the L-shape option: enter the full rectangle it would occupy, then the length and width of the missing corner. The cut-out is subtracted automatically.
What waste allowance should I add?
Between 5% and 10% for most materials, and 15% for diagonal tile layouts or rooms with many angles. It covers off-cuts, breakages and the piece you measure wrong.
Is my room list saved?
Only if you turn the save switch on, and then only in this browser. Nothing is uploaded — you can measure a whole house offline.