How do I calculate square metres from a room's dimensions?

For a simple rectangular room, multiply the length by the width, both measured in metres: area (m²) = length × width. A 5 m by 4 m room is 5 × 4 = 20 m². For other shapes — circles, regular pentagons, hexagons, or octagons — this calculator applies the matching formula automatically once you select the shape.

How do I work out the area of a circle in square metres?

Use Area = π × radius², where the radius is measured in metres. A circular area with a 2.5 m radius has an area of π × 2.5² ≈ 3.1416 × 6.25 ≈ 19.63 m². If you only know the diameter, halve it first to get the radius.

What is the formula for the area of a regular hexagon or octagon?

Both follow the general regular-polygon formula Area = (n × side²) / (4 × tan(π/n)), where n is the number of sides. For a hexagon (n=6) this works out to roughly 2.598 × side². For an octagon (n=8) it simplifies to 2 × (1 + √2) × side² ≈ 4.828 × side².

How many square metres is a 4 m by 4 m room?

A 4 m by 4 m square room is 16 m² (4 × 4 = 16). That's a common size for a small bedroom or home office.

How do I find the square metres of an irregularly shaped room?

Split the room into rectangles, circles, or other regular shapes you can calculate individually, work out the area of each section with this calculator, and add the results together. For an L-shaped room, that usually means splitting it into two rectangles along the internal corner.

How much does a professional area survey cost in the US?

A professional measurement or survey of a residential room or lot in the US typically costs between $150 and $450, depending on the property's size, shape, and accessibility.

Why would I need square meters instead of square feet in the US?

Square meters come up when pricing imported flooring, tile, or building materials quoted per m² by overseas suppliers, when comparing to an international property listing, or when working from architectural plans drawn to metric building codes. This calculator handles both units side by side.

Square Meter Calculator — Calculate Room Area in m²

How to Calculate Area in Square Metres

A square metre (m²) is the standard metric unit of area — a square exactly one metre long on each side — and it's the unit almost every country outside the US uses for flooring, tiling, land, and property listings. Unlike a plain rectangle-only tool, real rooms and plots come in more shapes than that: a square utility room, a circular patio, a pentagon-shaped bay window, or a hexagonal paving section all need their own formula, not just length times width.

This calculator handles all six of those shapes — square, rectangle, circle, regular pentagon, regular hexagon, and regular octagon — from a single shape selector. Pick your shape, enter the dimensions the form asks for (which change automatically depending on what you've chosen), and you get an instant area in square metres, plus a rough cost estimate for a professional measurement or survey if you need one.

People land on a square metre calculator for a wide range of reasons: a homeowner working out how much laminate flooring to order, a landlord confirming a listed floor area before an EPC or rental ad, a landscaper quoting a circular lawn or an octagonal deck, or a buyer sanity-checking a plot size on a property listing. Whatever the shape, the underlying task is the same — convert real-world dimensions into one clean, comparable m² figure.

Below we walk through exactly how each shape's inputs map onto its area formula, work through the maths by hand for two of the six shapes, and cover the measuring habits that cause the most costly mistakes.

How to Use the Square Metre Calculator

Start by choosing a shape from the Shape selector: Square, Rectangle, Circle, Regular pentagon, Regular hexagon, or Regular octagon. The input fields below update automatically to match your choice.
For a Square, Pentagon, Hexagon, or Octagon, enter the length of one side in the Side field — since these are regular shapes, every side is equal, so you only need to measure one edge.
For a Rectangle, enter both the Side / length and the Width — these can be measured and entered in different units if you need to (e.g. length in metres, width in centimetres); the calculator converts everything to a common unit before multiplying.
For a Circle, enter the Radius (the distance from the centre point to the edge) rather than the diameter. If you measured across the full width instead, halve that figure before entering it.
Each dimension field has its own unit dropdown (millimetres, centimetres, metres, feet, inches). You can mix units across fields in the same calculation — useful if part of your measurement came from a metric tape and part from an old imperial plan.
Read off the result: Area in square metres, updated instantly as you type. This tool measures area only — for a full material quantity and cost, feed the resulting m² figure into a dedicated flooring, tiling, or paint calculator.

The Area Formulas, Shape by Shape

Square: Area = side². A square with a 4 m side has an area of 4 × 4 = 16 m².

Rectangle: Area = length × width. This is the formula most people already know — a 5 m by 4 m room is 5 × 4 = 20 m².

Circle: Area = π × radius². A circular patio with a 3 m radius (6 m diameter) has an area of π × 3² ≈ 3.1416 × 9 ≈ 28.27 m².

Regular pentagon, hexagon, and octagon all share one general formula for a regular n-sided polygon with side length s: Area = (n × s²) / (4 × tan(π/n)). For a hexagon (n = 6), that simplifies to roughly Area ≈ 2.598 × s². For an octagon (n = 8), it simplifies to the well-known Area = 2 × (1 + √2) × s² ≈ 4.828 × s².

Worked example 1 (rectangle): a bedroom measures 5.2 m by 3.8 m. Area = 5.2 × 3.8 = 19.76 m². If you'd measured in centimetres instead — 520 cm by 380 cm — the calculator converts each to metres first (5.2 m and 3.8 m) before multiplying, so you get the identical 19.76 m² regardless of which unit you typed in.

Worked example 2 (regular hexagon): a hexagonal paving slab has 0.5 m sides. Using Area = (6 × 0.5²) / (4 × tan(π/6)) = (6 × 0.25) / (4 × 0.5774) = 1.5 / 2.3094 ≈ 0.6495 m² per slab. To cover a 10 m² patio you'd need roughly 10 ÷ 0.6495 ≈ 16 slabs, before accounting for cutting waste at the edges.

For an irregular room that isn't one of these six shapes — an L-shaped lounge, say — split it mentally into two or more of these regular shapes (typically rectangles), calculate each section's area with this calculator, and add the results together.

Quick-Reference Area Formulas

Keep this list handy for quick mental checks against the calculator's result:

Square (side s): A = s²
Rectangle (length l, width w): A = l × w
Circle (radius r): A = π × r² ≈ 3.1416 × r²
Regular pentagon (side s): A = (5 × s²) / (4 × tan(36°)) ≈ 1.7205 × s²
Regular hexagon (side s): A = (6 × s²) / (4 × tan(30°)) ≈ 2.5981 × s²
Regular octagon (side s): A = 2 × (1 + √2) × s² ≈ 4.8284 × s²

Pro Tips and Common Mistakes

Measure twice, especially for polygons: a regular pentagon, hexagon, or octagon only gives an accurate result if the sides really are equal length and the shape really is regular. A "hexagonal" garden bed that's slightly irregular in real life will read differently to how it calculates — treat the regular-polygon result as a close estimate, not an exact figure, for anything hand-built or informally laid out.

In the US, hiring a licensed surveyor or appraiser to professionally measure a residential room or lot typically costs between $150 and $450, depending on the size and accessibility of the property. A rectangular room measuring 5.2 m by 3.8 m (19.76 m², as in the worked example above) would sit toward the lower end of that range, while a full lot or an irregularly shaped parcel moves closer to $450. For everyday renovation, flooring, or tiling quotes, this calculator's instant m² figure is usually enough — a licensed survey matters most for a property sale, mortgage appraisal, or boundary dispute.

Although the US uses feet and inches for everyday construction, m² comes up whenever you're working from imported flooring/tile specs (many European and Asian manufacturers price per m²), international property listings, or metric building plans — this calculator lets you enter dimensions in feet or inches per field while still getting a clean square-metre result.

Circle inputs are the most common error source: this calculator asks for radius, not diameter. If you measured straight across the middle of a circular space, divide that number by two before entering it, or you'll get an area roughly four times too large.
For an irregular or L-shaped area, decompose it into two or more of the shapes above (usually rectangles), calculate each piece separately with this tool, and sum the results — don't try to force one shape's formula onto a space it doesn't actually describe.
Combining shapes also works in reverse: to find the area of a rectangular room with a semicircular bay window, calculate the rectangle and the circle (using half the circle's area) separately, then add them.
Keep units consistent within one calculation, or trust the calculator's per-field unit conversion rather than converting by hand — mixing metres and centimetres without converting is the single most common source of a wildly wrong square-metre figure.
For property or land measurements, remember that a professional land or floor-area survey may follow a specific national measurement standard that treats sloped ceilings, boundary walls, or garages differently to a simple hand measurement — use this calculator as a fast working estimate, not a substitute for a certified survey when one is legally required.