What is square footage?
Square footage is the measurement of a flat (2D) area in square feet. One square foot is the area of a 1 ft × 1 ft square. A room that's 12 feet long and 14 feet wide has 12 × 14 = 168 square feet of floor area.
The "square" in the name reflects the unit: you're measuring how many 1 ft × 1 ft tiles would cover the floor. Other countries use square metres (m²) — same idea, different size of tile. The conversion is 1 sq ft = 0.0929 m², or equivalently 1 m² = 10.764 sq ft.
Knowing your square footage is fundamental for almost any home project: ordering flooring, estimating paint, buying area rugs, sizing HVAC equipment, comparing apartments, listing a property for sale.
How to use the square footage calculator
- Pick the input unit at the top — feet, inches, metres, or centimetres. The same unit applies to every room you add.
- Enter the length and width of the first room (or area) in the fields.
- The room's individual area appears immediately below its inputs (in both sq ft and m²).
- Tap "+ Add another room" to add additional spaces. The calculator handles as many as you need.
- Watch the total at the bottom update as you add or modify rooms — shown in both sq ft (the US standard) and m² (the international standard).
- Tap Copy to grab the total in "X sq ft (Y m²)" format for your shopping list, contractor estimate, or rental listing.
Worked examples
Example 1 — Single 12 × 14 ft bedroom
Input: length 12, width 14, unit ft. Result: 168 sq ft (15.6 m²). A typical master bedroom. If you're carpeting it, order 168 sq ft + ~15% waste = ~195 sq ft of carpet.
Example 2 — A whole 3-bedroom apartment
Add four rooms:
- Living room: 16 × 18 = 288 sq ft
- Kitchen: 10 × 12 = 120 sq ft
- Bedroom 1: 12 × 14 = 168 sq ft
- Bedroom 2: 11 × 12 = 132 sq ft
Total: 708 sq ft (65.8 m²). A modest 3-bedroom apartment. The calculator does the addition automatically as you add rooms.
Example 3 — L-shaped living/dining room
Treat the L-shape as two rectangles. The 14 × 18 living-room portion + the 8 × 10 dining nook = 252 + 80 = 332 sq ft (30.8 m²). Add each rectangle as a separate "room" in the calculator.
Example 4 — A 100 m² European flat
Switch the unit to m. Enter rooms in metres. A 4 m × 5 m living room (20 m²) + 3 m × 4 m kitchen (12 m²) + 4 m × 4 m bedroom (16 m²) + 3 m × 3 m bedroom (9 m²) + 2 m × 3 m bathroom (6 m²) = 63 m² total = 678 sq ft. The calculator shows both, so you can list the place to either an American or European audience.
What you actually use the number for
Flooring
Tile, hardwood, laminate, carpet, vinyl plank — all sold by the square foot or square metre. Order your total area plus a waste allowance: 10% for straight installations, 15-20% for diagonal or pattern installs (herringbone, chevron). For 500 sq ft of straight-cut hardwood, order at least 550 sq ft.
Paint
Paint coverage is rated in sq ft per gallon — typically 350-400 sq ft per gallon per coat. To paint a 12 × 14 ft room with 8 ft ceilings: 4 walls × 12 × 8 + 4 walls × 14 × 8 = 832 sq ft of wall area. Subtract for doors and windows (~50 sq ft for a standard door + 1 window = 782 sq ft). At 350 sq ft per gallon: about 2.2 gallons for one coat, 4.5 gallons for two coats (most paints recommend two).
HVAC sizing
Air conditioner BTU sizing rule of thumb: 20 BTU per sq ft. A 1500 sq ft house needs roughly a 30,000 BTU system (a 2.5-ton unit). Heaters use a similar rule — typically 30-40 BTU per sq ft depending on insulation and climate.
Real estate
Apartment and house listings quote square footage prominently. A "1200 sq ft 2BR/2BA" gives the buyer or renter an instant size sense. Note: definitions vary — some markets include closets, balconies, and basements; others don't. Check your local norm before quoting a number on a listing.
Rent comparison
Different apartments are easier to compare on a $/sq ft basis. A $2400/month 1BR apartment of 700 sq ft is $3.43/sq ft/month. A $2800/month 2BR of 950 sq ft is $2.95/sq ft/month — better value per square foot. The calculator gives you the denominator.
Property tax and insurance
Both are influenced by total interior square footage. An accurate measurement matters for tax assessments and replacement-cost insurance estimates.
Handling non-rectangular rooms
Most rooms are rectangular, but some aren't. Strategies:
- L-shape — break into two rectangles. Add them as two rooms in the calculator. Same for U-shape (three rectangles), T-shape (two), etc.
- Triangular alcove — area = ½ × base × height. Add the result manually as a "room" with the calculator showing each sub-area.
- Circular bay window — area = πr² for a full circle, or a fraction for a sector. Compute separately and add to total.
- Trapezoidal hallway — area = ½ × (parallel side 1 + parallel side 2) × perpendicular distance.
- Genuinely irregular — divide into smaller rectangles and triangles, compute each, sum. The more pieces, the better the approximation.
Should you include every space?
Depends on what you're using the number for:
- Flooring/paint/HVAC: include every space that gets material. Closets, hallways, and bathrooms all count.
- Real estate listings: definitions vary by market. ANSI Z765 (the US standard) includes only finished above-grade interior space measured at the exterior wall. Garages, unfinished basements, attics, balconies, and closets are typically excluded for this measure but may be reported separately.
- Rent comparison: stay consistent. Compare apples-to-apples (gross sq ft for both, or net interior for both).
- Property tax: follow the assessor's rules — they're usually published.
Mixing imperial and metric
The calculator's unit picker applies one unit to every room. If your rooms are mixed (a US apartment with a balcony measured in metric, say), convert everything to one unit first. The calculator shows the total in both sq ft and m² regardless — so you can pick whichever input unit feels natural and read the output in whatever unit your audience expects.
Common mistakes
- Confusing area with perimeter. Square footage = length × width (a single number, in squared units). Perimeter = 2 × (length + width) (a different number, in linear units). Use perimeter for trim, baseboard, and weather stripping; use area for floor materials.
- Forgetting to subtract for cabinets, fixtures, and built-ins. If you're estimating flooring, the floor under your kitchen island doesn't need flooring. Subtract built-in fixtures from your total.
- Skipping the waste allowance. Buying exactly your calculated square footage means you'll run out before you finish. Add 10-20% waste depending on install complexity.
- Mixing units mid-calculation. Length in feet × width in inches gives garbage. Convert to one unit first.
- Counting the wall area as floor area. Wall area (for painting) and floor area (for flooring) are different measurements — don't confuse them.
What the calculator gives you, summarized
- Per-room area — shown alongside each room as you enter dimensions, in both sq ft and m².
- Running total — sum across all rooms, updated as you add or modify entries.
- Both unit systems — total displayed in sq ft (US) AND m² (international) so you don't have to convert by hand.
- Multi-unit input — pick from ft, in, m, or cm based on how you measured.
- Unlimited rooms — add as many sub-areas as you need to capture an irregular layout.
Whether you're flooring a closet or estimating an entire house, the math is the same and the calculator handles the addition for you.