A square footage calculator finds the area of a room, floor, wall, or yard in square feet from simple measurements. To calculate square footage, pick a shape — rectangle, circle, or triangle — enter the dimensions in feet, and get the area instantly, along with conversions to square yards, square meters, and acres.
Square footage drives most home-project math: flooring and carpet are quoted per square foot or square yard, paint coverage is rated in square feet per gallon, and real estate is priced and compared per square foot. Add an optional price per square foot to turn the measured area straight into a material cost estimate.
How to Calculate Square Feet: Rectangle, Circle, and Triangle
Each shape has a standard area formula, with all measurements in feet:
- Rectangle or square: Area = Length × Width
- Circle: Area = π × r², where r is the radius (half the diameter)
- Triangle: Area = ½ × Base × Height, where height is measured perpendicular to the base
Unit conversions from square feet: divide by 9 for square yards (carpet is often quoted this way), multiply by 0.0929 for square meters, and divide by 43,560 for acres.
If you measured in inches, divide each dimension by 12 before multiplying — or multiply the areas: a 30 in × 48 in tabletop is 2.5 ft × 4 ft = 10 sq ft.
How to Calculate Square Feet of a Room, Including L-Shapes
For a simple rectangular room, measure the length and width along the floor at the baseboards with a tape measure and multiply. Measure to the nearest half inch and round up slightly — coming up short on flooring is far worse than a little extra.
For an L-shaped or irregular room, split it into rectangles: measure each rectangular section separately, calculate each area, and add them. An L-shaped room made of a 12 × 10 ft section and a 6 × 8 ft section is 120 + 48 = 168 sq ft.
Buying materials, add a waste factor: 5%–10% extra for flooring and tile laid straight, and 15% for diagonal patterns, complex cuts, or natural stone. Closets and alcoves count too — walk the whole footprint.
Example: Flooring a 15 × 12 ft Living Room
A living room measures 15 ft long by 12 ft wide.
Area = 15 × 12 = 180 sq ft, which is 20 square yards or about 16.7 square meters.
With laminate flooring at $3.50 per square foot, the base material cost is 180 × $3.50 = $630. Adding a 10% waste factor means buying about 198 sq ft, or roughly $693 of material.
For paint, the relevant area is the walls: with 8 ft ceilings, the wall area is the perimeter (15 + 12 + 15 + 12 = 54 ft) × 8 = 432 sq ft. Since one gallon typically covers 350–400 sq ft per coat, two coats need about 2.5 gallons.
Converting Square Feet to Other Units
Every conversion out of square feet is a fixed factor, because the underlying units are exact definitions:
- Square inches: multiply by 144 (12 × 12 inches to the foot)
- Square yards: divide by 9 (3 × 3 feet to the yard) — how carpet is usually priced
- Square meters: multiply by 0.09290304 exactly, since a foot is exactly 0.3048 m
- Acres: divide by 43,560, the number of square feet in an acre
Going the other way, multiply instead of divide: 1 square meter is 10.7639 sq ft, 1 square yard is 9 sq ft, and 1 acre is 43,560 sq ft.
The acre figures people look up most often:
- Quarter acre = 10,890 sq ft
- Half acre = 21,780 sq ft
- Full acre = 43,560 sq ft
- 10,000 sq ft = 0.2296 acres, just under a quarter acre
The 43,560 figure looks arbitrary but comes from the old measure of an acre as one chain (66 ft) by one furlong (660 ft): 66 × 660 = 43,560.
| Square feet | Square inches | Square yards | Square meters | Acres |
|---|---|---|---|---|
| 1 sq ft | 144 | 0.1111 | 0.0929 | 0.000023 |
| 10 sq ft | 1,440 | 1.1111 | 0.929 | 0.00023 |
| 100 sq ft | 14,400 | 11.11 | 9.29 | 0.0023 |
| 500 sq ft | 72,000 | 55.56 | 46.45 | 0.0115 |
| 1,000 sq ft | 144,000 | 111.11 | 92.90 | 0.0230 |
| 5,000 sq ft | 720,000 | 555.56 | 464.52 | 0.1148 |
| 10,000 sq ft | 1,440,000 | 1,111.11 | 929.03 | 0.2296 |
| 43,560 sq ft | 6,272,640 | 4,840 | 4,046.86 | 1.0000 |
Linear Feet vs. Square Feet
These get confused constantly, and they measure different things. Linear feet measure length along a single line. Square feet measure area, which needs two dimensions.
You cannot convert linear feet to square feet without knowing the width. The formula is:
Square feet = Linear feet × Width in feet
So 100 linear feet of material that is 6 inches (0.5 ft) wide covers 50 sq ft. The same 100 linear feet at 3 ft wide covers 300 sq ft — six times the area from the identical length.
Where each unit is actually used:
- Linear feet: trim, baseboard, crown moulding, fencing, countertop edging, lumber
- Square feet: flooring, carpet, tile, drywall, paint coverage, roofing, sod
The practical trap is buying flooring quoted per square foot when the supplier ships it in planks measured in linear feet. Always convert using the actual plank width before ordering, and note that some materials are sold by the "board foot," which is a volume measure that also involves thickness.
How Big Is 1,000 Square Feet? Common Sizes Visualised
Square footage on its own is hard to picture, which is why the same number can feel very different in practice. A 1,000 sq ft apartment laid out as 25 × 40 ft feels quite unlike a 31.6 ft square of the same area.
A useful reference point: a standard one-car garage bay is roughly 200 sq ft, so you can count garages. 1,000 sq ft is about five of them.
For a quick estimate of any space, pace it out. An average adult step is roughly 2.5 ft, so a room that takes 12 steps one way and 8 the other is about 30 × 20 ft, or 600 sq ft. Not precise enough to order flooring, but enough to sanity-check a listing.
| Area | As a square | A typical shape | Square meters |
|---|---|---|---|
| 100 sq ft | 10 × 10 ft | Small bedroom | 9.3 |
| 200 sq ft | 14.1 × 14.1 ft | One-car garage bay | 18.6 |
| 400 sq ft | 20 × 20 ft | Studio apartment | 37.2 |
| 500 sq ft | 22.4 × 22.4 ft | Large studio | 46.5 |
| 800 sq ft | 28.3 × 28.3 ft | One-bedroom apartment | 74.3 |
| 1,000 sq ft | 31.6 × 31.6 ft | 25 × 40 ft, two-bedroom | 92.9 |
| 1,500 sq ft | 38.7 × 38.7 ft | 30 × 50 ft, three-bedroom | 139.4 |
| 2,000 sq ft | 44.7 × 44.7 ft | 35 × 57 ft, family home | 185.8 |
| 2,500 sq ft | 50 × 50 ft | Large family home | 232.3 |
The "as a square" column is the square root of the area — the dimensions if the space were perfectly square. Real rooms are rectangular, so the same square footage comes in many shapes.
Roof and Sloped-Surface Square Footage
A roof always has more surface area than the building footprint underneath it, because the slope stretches the distance. Measuring the footprint from the ground and using that figure will under-order materials.
The correction is a pitch multiplier:
Roof area = Footprint area × √(1 + (rise ÷ 12)²)
For a 6/12 pitch, which rises 6 inches for every 12 inches of run, the multiplier is √(1 + 0.25) = 1.118. A 1,500 sq ft footprint therefore needs about 1,677 sq ft of roofing — 12% more than the ground measurement suggests.
Roofing is ordered in "squares," where one square is 100 sq ft of roof surface. That 1,677 sq ft roof is about 17 squares, and suppliers expect the order in those units.
Add 10–15% for waste, more for a roof with valleys, dormers or hips, since each one produces off-cuts. For anything structural or safety-related, confirm quantities with your roofer rather than a calculator alone.
| Roof pitch | Multiplier | 1,500 sq ft footprint becomes |
|---|---|---|
| 3/12 (low) | 1.031 | 1,546 sq ft |
| 4/12 | 1.054 | 1,581 sq ft |
| 5/12 | 1.083 | 1,625 sq ft |
| 6/12 (common) | 1.118 | 1,677 sq ft |
| 8/12 | 1.202 | 1,803 sq ft |
| 10/12 | 1.302 | 1,953 sq ft |
| 12/12 (45°) | 1.414 | 2,121 sq ft |
Frequently Asked Questions
How do you calculate square feet of a room?
Measure the room’s length and width in feet and multiply them together. A 15 ft by 12 ft room is 180 square feet. For irregular rooms, break the space into rectangles, calculate each area separately, and add them up. Measurements in inches should be divided by 12 first.
How do I convert square inches to square feet?
To go from sq in to sq ft, divide the square inches by 144, because a square foot is 12 × 12 = 144 square inches. So 1,000 sq in is 6.94 sq ft. Going the other way, multiply square feet by 144: a 10 sq ft panel is 1,440 sq in. Note that you divide by 144, not 12 — that is the most common mistake in area conversions.
How many square feet are in an acre?
43,560 square feet. A quarter acre is 10,890 sq ft, half an acre is 21,780 sq ft, and 10,000 sq ft is 0.2296 acres — just under a quarter acre. The odd 43,560 figure comes from the historic definition of an acre as one chain (66 ft) by one furlong (660 ft).
How do I convert linear feet to square feet?
Multiply the linear feet by the width in feet — you cannot convert without knowing the width. 100 linear feet of 6-inch-wide (0.5 ft) planking covers 50 sq ft, while the same 100 linear feet at 3 ft wide covers 300 sq ft. Linear feet measure length only; square feet measure area.
How do I convert square feet to cubic yards?
Multiply the square footage by the depth in feet, then divide by 27 (the cubic feet in a cubic yard). For 1,000 sq ft at 4 inches deep: 1,000 × (4 ÷ 12) ÷ 27 = 12.35 cubic yards. This is the calculation for ordering concrete, gravel, mulch, or topsoil.
How do I calculate the square footage of a building?
Measure the exterior length and width of each rectangular section at ground level, multiply each pair, and add the sections together. For multi-storey buildings, calculate each floor separately and total them. Measure to the outside of the walls for gross area, or the inside for usable floor area — listings and appraisals use different conventions, so check which one is being asked for.
How big is 1,000 square feet?
About 31.6 × 31.6 ft if perfectly square, or 25 × 40 ft in a typical rectangular layout — roughly 92.9 square meters, or about five one-car garage bays. It commonly corresponds to a two-bedroom apartment or small house.
How do I calculate roof square footage?
Multiply the building footprint by a pitch multiplier, since a sloped roof has more surface than the ground beneath it. For a 6/12 pitch the multiplier is √(1 + 0.25) = 1.118, so a 1,500 sq ft footprint needs about 1,677 sq ft of roofing. Roofing is ordered in "squares" of 100 sq ft each, so that is roughly 17 squares plus waste.
How much does carpet cost per square foot?
Costs vary widely by material and region, so use your own quoted price. The method is what matters: multiply your square footage by the price per square foot, then add 5–10% for waste on straight installs or 15% for diagonal patterns. Note that US carpet is often quoted per square yard — divide square feet by 9 first to compare prices fairly.
How many square feet is 40 square meters?
430.56 square feet. One square meter is 10.7639 sq ft, because a foot is exactly 0.3048 m and 0.3048² = 0.09290304. To go the other way, multiply square feet by 0.0929.
How many square feet are in a square yard?
There are 9 square feet in a square yard, because a yard is 3 feet and 3 × 3 = 9. To convert square feet to square yards, divide by 9: a 180 sq ft room is 20 square yards. Carpet in the US is often priced per square yard, so this conversion comes up constantly.
How do I calculate the square footage of an L-shaped room?
Split the L into two rectangles, measure each one, and add the areas. For example, a main section of 12 × 10 ft (120 sq ft) plus an extension of 6 × 8 ft (48 sq ft) totals 168 sq ft. Any irregular straight-walled room can be handled this way by dividing it into rectangles.
How much extra flooring should I buy for waste?
Buy 5%–10% more than the measured square footage for standard straight installations, and about 15% extra for diagonal layouts, herringbone patterns, rooms with many corners, or natural materials with defects. The extra covers cutting waste, mistakes, and future repairs from the same dye lot.
Does square footage of a house include all rooms?
Listed square footage generally covers finished, heated, above-grade living space measured from the exterior walls. Garages, unfinished basements, attics, and open porches are usually excluded, though finished basements are often listed separately. Standards vary by region, so appraisals typically follow the ANSI Z765 standard.