Room Size Calculator
A room size calculator converts your room's dimensions into square footage so you know exactly how much flooring, paint, or carpet to buy. Select your room shape, enter the measurements in the panel, and get an instant result — no math required.
What Is a Room Size Calculator?
A room size calculator determines the floor area of a room in square feet or square meters based on the room's dimensions. Square footage is the standard measurement used for flooring, carpet, tile, paint, and real estate listings in the United States. Knowing the exact square footage of a room prevents costly mistakes — buying too little flooring means a second trip to the store, while buying too much wastes money.
Room size calculators are used by homeowners planning renovations, renters measuring spaces for furniture, contractors estimating materials, and real estate agents calculating total living area. The tool supports rectangular rooms, L-shaped open-plan layouts, circular sunrooms, and triangular corner spaces. For meeting and event spaces specifically, see our meeting room size calculator which calculates capacity based on room area.
How the Room Size Calculator Works
Rectangular Rooms
Most rooms are rectangular. To calculate the area, multiply the length by the width. A 12-foot by 14-foot bedroom has an area of 12 × 14 = 168 square feet. Measure along the longest wall for length and the adjacent wall for width. Include closets if you are buying flooring for the entire floor, or exclude them if you are only measuring the open area.
L-Shaped Rooms
L-shaped rooms are common in open-plan kitchens and living rooms. Divide the L-shape into two separate rectangles, measure each section independently, then add the two areas together. For example, a living room with a 16×12 ft main section and an 8×10 ft alcove has a total area of 192 + 80 = 272 square feet. Make sure you do not double-count the corner where the two rectangles overlap.
Circular Rooms
Circular rooms such as sunrooms, turrets, or rotundas require the diameter measurement (the full width across the center of the circle). The area equals π × radius², where the radius is half the diameter. A circular room 15 feet in diameter has a radius of 7.5 feet and an area of π × 7.5² ≈ 176.7 square feet. This is also used when tiling circular patios or installing round area rugs. See our circle calculator for additional circle measurements including circumference and diameter.
Triangular Rooms
Triangular rooms appear in attic conversions, loft spaces, and corner extensions. The area equals half the base multiplied by the height: Area = 0.5 × base × height. A triangular attic floor with a 20-foot base and 12-foot perpendicular height has an area of 0.5 × 20 × 12 = 120 square feet. The height must be measured perpendicularly from the base to the opposite corner, not along a sloped wall.
How to Measure a Room
Tools You Need
For accurate measurements, use a tape measure (at least 25 feet long for larger rooms), a laser distance measurer for long distances or high-accuracy needs, pencil and paper to record measurements, and a calculator or this tool to compute the area. Laser measurers are particularly useful in empty rooms where holding one end of a tape measure against a wall is difficult alone.
Measuring Length and Width
Measure along the floor from wall to wall. For the most accurate reading, measure in multiple spots — walls in older homes are rarely perfectly straight, and the measurements may vary by an inch or two. Use the longest measurement to ensure you have enough material. Always measure in feet and inches, then convert partial inches to decimal feet (e.g., 12 feet 6 inches = 12.5 feet) before calculating area.
Handling Odd Shapes
For rooms that do not fit neatly into standard shapes, break the floor plan into multiple simple shapes, calculate each area separately, and sum the results. A room with a bay window extension, for example, can be measured as the main rectangle plus a smaller rectangle for the bay. Rooms with cutouts or alcoves can be measured as the full rectangle minus the missing section. For complex floor plans, our area calculator and polygon area calculator handle additional shape types.
Square Footage Formula
The formulas used by this calculator for each room shape:
To convert between square feet and square meters: 1 square meter = 10.764 square feet. To convert from square feet to square meters, divide by 10.764. To convert from square meters to square feet, multiply by 10.764.
Room Size Chart
Common room types and their typical dimensions and square footage in US homes:
| Room Type | Typical Dimensions | Square Footage |
|---|---|---|
| Small Bedroom | 10 × 10 ft | 100 sq ft |
| Standard Bedroom | 12 × 14 ft | 168 sq ft |
| Master Bedroom | 15 × 20 ft | 300 sq ft |
| Small Living Room | 12 × 18 ft | 216 sq ft |
| Large Living Room | 20 × 25 ft | 500 sq ft |
| Small Kitchen | 8 × 10 ft | 80 sq ft |
| Large Kitchen | 15 × 20 ft | 300 sq ft |
| Bathroom (Small) | 5 × 8 ft | 40 sq ft |
| Dining Room | 12 × 14 ft | 168 sq ft |
| Home Office | 10 × 12 ft | 120 sq ft |
| Garage (1-car) | 12 × 22 ft | 264 sq ft |
| Garage (2-car) | 22 × 24 ft | 528 sq ft |
Paint Calculator by Room Size
How Much Paint Per Square Foot
One gallon of paint covers approximately 350 to 400 square feet of smooth surface in a single coat. Textured walls, porous surfaces like brick, and new drywall absorb more paint, reducing coverage to 300 to 350 square feet per gallon. For most rooms, you will need two coats, which doubles the total paint required. When changing from a dark color to a light color, a primer coat is recommended before the final color coat, adding a third gallon requirement.
Calculating Wall Area vs Floor Area
Paint is applied to walls, not floors, so you need to calculate wall area separately from floor area. For a rectangular room, wall area equals the perimeter multiplied by ceiling height, minus the area of doors and windows. For a standard 12×14 room with 8-foot ceilings: perimeter = 2 × (12 + 14) = 52 feet. Wall area = 52 × 8 = 416 sq ft. Subtract two standard doors (2 × 20 = 40 sq ft) and two windows (2 × 15 = 30 sq ft) = approximately 346 sq ft of paintable wall. That is roughly one gallon per coat. Buy two gallons for two coats plus a small buffer.
Flooring Calculator by Room Size
How to Calculate Flooring Needed
Flooring is sold in square feet. To find how much you need, calculate the room's floor area and add a waste factor. For straight-lay installations like most vinyl plank and tile, a 10% waste factor is standard. For diagonal tile or herringbone hardwood patterns, use a 15% waste factor due to the additional cuts required. For carpet, add 10% to 15% depending on room shape and seam placement.
Hardwood flooring is typically sold in square feet on individual packages. Tile is sold by the square foot or per box (note the coverage per box). Carpet is usually sold by the square yard — divide your square footage by 9 to convert to square yards.
Adding Waste Factor (10%)
The standard waste factor formula is: Total flooring needed = Room area × 1.10 (for 10% waste). A 168 sq ft bedroom requires 168 × 1.10 = 184.8, rounded up to 185 sq ft of flooring. Always round up to the nearest full unit (box or plank). The waste factor accounts for cuts at walls, irregularly shaped areas, mistakes during installation, and material reserved for future repairs.
Room Size Calculator Examples
Example 1 — 12×14 Bedroom
A standard bedroom measures 12 feet wide and 14 feet long. Area = 12 × 14 = 168 square feet. Flooring with 10% waste: 185 sq ft. Paint for floor: less than 1 gallon. For walls with 8-foot ceilings: perimeter = 2 × (12 + 14) = 52 ft. Wall area = 52 × 8 = 416 sq ft minus doors and windows (approx 50 sq ft) = 366 sq ft. You need roughly 1 gallon per coat. Budget 2 gallons for two coats. This room comfortably fits a queen or king bed, dresser, and two nightstands.
Example 2 — L-Shaped Living Room
An open-plan living room has a main section of 20×15 ft (300 sq ft) and a dining alcove of 12×10 ft (120 sq ft). Total area = 300 + 120 = 420 square feet. Flooring with 10% waste: 462 sq ft. This is roughly 43 square yards of carpet. The combined space is suitable for a sectional sofa, coffee table, dining table for 6, and entertainment center without feeling crowded.
Example 3 — Circular Sunroom, 15ft Diameter
A circular sunroom with a diameter of 15 feet has a radius of 7.5 feet. Area = π × 7.5² = 3.14159 × 56.25 = ≈ 176.7 square feet. Flooring needed with 10% waste: 195 sq ft. Because tile must be cut to fit the curved perimeter, a 15% waste factor is recommended, giving 204 sq ft. Circular rooms require special attention for flooring — a diagonal or radial tile pattern complements the round shape better than a straight grid.
Frequently Asked Questions
How do I calculate square footage?
For a rectangular room, multiply the length by the width: Area = Length × Width. For a 12×15 room, that's 180 square feet. For L-shaped rooms, split into two rectangles and add the areas. For circular rooms, use Area = π × radius². For triangular rooms, use Area = 0.5 × base × height. Always measure in feet for results in square feet.
What is the average bedroom size?
The average bedroom in a US home is between 132 and 168 square feet, with dimensions typically around 11×12 ft to 12×14 ft. A small or secondary bedroom is typically 100 to 120 square feet (10×10 or 10×12). A primary or master bedroom in newer homes averages 200 to 400 square feet. The minimum bedroom size most building codes require is 70 square feet with at least one dimension of 7 feet.
How much paint do I need for a 12×12 room?
A 12×12 room has a floor area of 144 square feet. For painting the walls at 8-foot ceiling height: perimeter = 2 × (12 + 12) = 48 ft. Wall area = 48 × 8 = 384 sq ft, minus doors and windows (approximately 50 sq ft) = 334 sq ft. At 350 sq ft per gallon, you need about 1 gallon per coat. Buy 2 gallons for two coats. Add a third gallon if also painting the ceiling (144 sq ft extra).
How do I calculate square footage for an L-shaped room?
Divide the L-shape into two rectangles by drawing an imaginary straight line. Measure the length and width of each rectangle separately, calculate each area (length × width), then add both areas together. For example, a room with a 15×12 section (180 sq ft) and an 8×10 section (80 sq ft) has a total area of 260 square feet. Make sure you do not include the corner area in both measurements.
What is the difference between square feet and linear feet?
Square feet measure area (a two-dimensional surface), calculated as length × width. Linear feet measure length only in one dimension. You use square feet when buying flooring, tile, or paint. You use linear feet when buying baseboards, crown molding, fence panels, or fabric sold by the running foot. A 12×14 room has 168 square feet of floor area but 52 linear feet of perimeter (for baseboards). The two units are not interchangeable.