How this works
A square-footage calculator is the workhorse tool for any project priced by area: flooring, paint, carpet, tile, sod, mulch, or rent-per-square-foot quotes. The math is just length × width per rectangular section, summed across all sections. The wrinkle is units — the US still quotes interior space in square feet (ft²); the UK uses both ft² and m² depending on context (residential is shifting to m²); the rest of the world is metric (m²). This tool accepts either unit and shows results in both, plus acres for larger lots. Three practical patterns. (1) For an L-shaped room or any non-rectangular space, divide it into rectangles, measure each, and sum. The calculator supports multiple rooms for exactly this. (2) For walls (paint, wallpaper), what you actually need is wall area, not floor area — measure each wall as height × width, subtract doors and large windows, sum across the four walls. The same widget works; just enter wall dimensions instead of floor. (3) When ordering material, add 10% waste for square cuts (carpet, vinyl) and 15% for diagonal patterns or tile — manufacturers ship in standard widths and you'll cut off-cuts. Unit conversions worth memorising. 1 m² = 10.764 sq ft (or "about 10.8"). 1 sq ft = 0.0929 m². 1 acre = 43,560 sq ft = 4,047 m² (about 16 tennis courts or 60% of an American football field). 1 hectare = 10,000 m² = 2.471 acres. UK floor space is sometimes quoted in "tsubo" — a Japanese unit equal to 3.306 m² or 35.58 sq ft (the area of two tatami mats); JP property listings still use it routinely alongside m².
The formula
For non-rectangular shapes, divide into rectangles and add a row per section. Triangle (½ × base × height), circle (π × radius²), and trapezoid (½ × (a + b) × height) areas can be added as a single line item using their pre-computed area. The unit toggle controls input units (ft or m); the output always shows both.
Example calculation
- Living room: 18 ft × 14 ft = 252 sq ft
- Bedroom: 12 ft × 11 ft = 132 sq ft
- Kitchen: 10 ft × 12 ft = 120 sq ft
- Total: 504 sq ft = 46.8 m². Add 10% waste for flooring → order 555 sq ft.
Frequently asked questions
How do I measure an L-shaped or irregular room?
Split it into rectangles. Most awkward rooms are two or three rectangles glued together. Sketch the room from above, draw the dividing lines, measure each rectangle's length × width, and add a row per rectangle to the calculator. For curves or true diagonals, treat them as triangles (½ × base × height) and add the result as a single line item. For accurate flooring orders, err on the side of one extra rectangle rather than rounding up everything.
How much waste should I add when ordering flooring or tile?
Standard rule: 10% for straight cuts (rectangular vinyl planks, laminate, wide-plank wood, simple tile patterns) and 15% for diagonal layouts, herringbone, or busy mosaic tile. Bump to 20% for very small rooms (under 100 sq ft) where every cut wastes more, or for rooms with lots of cutouts (around toilets, kitchen islands). Order all materials from the same dye lot at once — getting a top-up of 5 sq ft three weeks later means a visible colour mismatch on most products.
How do I measure for paint instead of flooring?
Measure each wall's height × width and add it as a separate row, then subtract doors (about 21 sq ft / 2 m² each) and large windows (about 15 sq ft / 1.4 m² each). Don't subtract small windows or trim — they'll be in the noise. Most interior latex paint covers 350–400 sq ft (32–37 m²) per gallon for one coat on smooth drywall; bare or porous surfaces drink more. Plan for two coats unless you're going same-colour-on-same-colour.
When do I need acres or hectares instead of sq ft / m²?
Roughly: anything above 5,000 sq ft (465 m²) starts to feel awkward in small units. Land plots, farms, parks, commercial sites, and parking lots are typically quoted in acres (US/UK rural) or hectares (most of the rest of the world). 1 acre = 43,560 sq ft = 4,047 m² (roughly the size of a US football field minus the end zones). 1 hectare = 10,000 m² = 2.471 acres = 107,639 sq ft. Residential lots in US suburbs are typically 0.1–0.5 acres; UK back gardens are smaller (often quoted in m² up to ~1,000 m², then in acres). The calculator above shows acres automatically when totals exceed ~5,000 sq ft.