Quick answer
Square footage is length times width, with both in the same unit: a 12 ft by 10 ft room is 120 square feet. Enter the two dimensions and choose the unit and the calculator returns the area in square feet, square metres and square yards.
The calculator handles rectangles only. For an L-shaped or irregular room, split it into rectangles, calculate each and add the areas.
Related tools: Cubic Yards Calculator: Cubic yards, cubic feet and cubic meters from length, width and height. Concrete Calculator: Cubic yards of concrete for a slab, plus bag counts. Gravel Calculator: Cubic yards of gravel for an area.
How to use the Square Footage Calculator
- Enter length (above 0).
- Enter width (above 0).
- Choose unit: Feet, Inches, Yards, Metres and Centimetres.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Length | A number | > 0 |
| Width | A number | > 0 |
| Unit | Choose one: Feet; Inches; Yards; Metres; Centimetres | Starts at Feet |
Formula and method
Formula
area = length × width, converted to ft² using exact factors
IEEE-754 double precision; shown to at most 6 decimal places.
1 ft = 0.3048 m exactly.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Length = 12; Width = 10; Unit = Feet.
| Result | Value |
|---|---|
| Area | 120 ft² |
| Square metres | 11.1484 |
| Square yards | 13.3333 |
Example 2
Inputs: Length = 5; Width = 4; Unit = Metres.
| Result | Value |
|---|---|
| Area | 215.2782 ft² |
| Square metres | 20 |
| Square yards | 23.9198 |
The first line is the headline result (area). Below it the square Footage Calculator lists square metres and square yards, which describe the same case from other angles. IEEE-754 double precision; shown to at most 6 decimal places.
Units and conversions
Mixing units is the main error: 12 feet times 120 inches is not an area in any unit. Convert first, using 12 inches to the foot, or enter both values in one unit. Metric uses the exact definition 1 foot = 0.3048 metre, so a room 3.658 m by 3.048 m is about 12 ft by 10 ft, or 120 square feet.
The same numbers (12 by 10) in different units
Every figure in this table comes from running this calculator, so it matches what the form returns.
| Unit | Area | Square metres |
|---|---|---|
| Feet | 120 | 11.1484 |
| Yards | 1,080 | 100.3353 |
| Metres | 1,291.6693 | 120 |
| Inches | 0.8333 | 0.0774 |
| Centimetres | 0.1292 | 0.012 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Length: entering "0" shows "Length must be greater than 0." beside that field and no result.
Choosing between the Square Footage Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Cubic Yards Calculator](/construction/cubic-yards-calculator/) | length, width and height or depth | Volume |
| [Concrete Calculator](/construction/concrete-calculator/) | length, width and depth / thickness | Cubic yards |
| [Gravel Calculator](/construction/gravel-calculator/) | length, width and depth / thickness | Cubic yards |
| [Mulch Calculator](/construction/mulch-calculator/) | length, width and depth / thickness | Cubic yards |
| [Board Foot Calculator](/construction/board-foot/) | thickness, width and length | Board feet |
Background: construction estimates
Material quantities are geometry plus a margin. Calculate the exact volume or area, add an allowance for waste, spillage, cuts and uneven ground (calculator pages commonly mention 5 to 10 percent, a rule of thumb that varies by material and job) and round up to whole units. One cubic yard is exactly 27 cubic feet.
Suppliers often have minimum order sizes and may charge for small loads, so confirm quantities, product yields and local code with your supplier or a qualified estimator before ordering.
Assumptions and limitations
- Rectangles only
Quantities are estimates. Add allowances for waste and site conditions, and follow local codes and a qualified professional's instructions for structural or safety-critical work.
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for length to confirm this.
Frequently asked questions
How do I find the square footage of an L-shaped room?
Split the room into two rectangles, find the area of each with length times width and add them together.
What does the Square Footage Calculator calculate?
Area of a rectangular space in square feet, square metres and square yards. It returns Area, Square metres and Square yards.
What formula does the Square Footage Calculator use?
area = length × width, converted to ft² using exact factors. 1 ft = 0.3048 m exactly.
What do I need to enter in the square Footage Calculator?
You enter Length, Width and Unit.
How is the result rounded or limited?
IEEE-754 double precision; shown to at most 6 decimal places. Rectangles only.
What does the “Unit” option change?
It sets how the square Footage is worked out. The choices are Feet, Inches, Yards, Metres and Centimetres.
What is an example of a square Footage result?
With length 12, width 10 and unit Feet, the area is 120 ft².
Can I rely on this calculator for a decision?
Quantities are estimates. Add allowances for waste and site conditions, and follow local codes and a qualified professional's instructions for structural or safety-critical work. For this calculator in particular: Rectangles only.
Related calculators
- Cubic Yards Calculator — Cubic yards, cubic feet and cubic meters from length, width and height.
- Concrete Calculator — Cubic yards of concrete for a slab, plus bag counts.
- Gravel Calculator — Cubic yards of gravel for an area.
- Mulch Calculator — Cubic yards of mulch for a bed.
- Board Foot Calculator — Board feet of lumber from thickness, width and length.
- Soil Calculator — Cubic yards of soil for an area.
- Sand Calculator — Cubic yards of sand for an area.
Sources
- OpenStax, University Physics Volume 1 (Rice University): mechanics
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.