Alltag

Flächenrechner

Form wählen, Maße eingeben — Fläche in m² und ft².

Berechnen

Measurements convert when you switch units

m
m
m
m
m
m
m
m

Updates as you type

Ergebnis

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Die Formel

Rectangle area is length × width. Circle area is πr² (π ≈ 3.14159…). Triangle area is ½ × base × height, or Heron’s formula from three sides: s = (a+b+c)/2, area = √[s(s−a)(s−b)(s−c)]. Results convert with 1 m² ≈ 10.7639 ft².

A = L×W · A = πr² · A = ½bh · A = √[s(s−a)(s−b)(s−c)]

Rechenbeispiel

  1. Rectangle 5 m × 4 m → 20 m²
  2. Circle r = 2 m → π×4 ≈ 12.57 m²
  3. Triangle base 6 m, height 3 m → ½×6×3 = 9 m²

Ergebnis: Shape formulas with automatic m²/ft² display

How multi-shape area is calculated

Each mode applies the standard Euclidean area formula for that shape, then converts between square metres and square feet.

Rectangle and circle

A rectangle (or rectangular room section) is length times width in the same unit. A circle uses πr² with the radius measured to the rim — diameter ÷ 2 if you only know the diameter.

Triangles

When you know a base and the perpendicular height to that base, use ½bh. When you know all three side lengths, Heron’s formula applies — but only if the sides satisfy the triangle inequality (each side shorter than the sum of the other two).

Units

Metric mode expects metres and reports m² first. Imperial mode expects feet and reports ft² first. Mixed units (e.g. metres × feet) are not converted automatically — convert sides first.

What we do not model

No flooring waste factor, wall paint area, or GIS survey feet. For legal property area, use a surveyor’s plan.

Interessante Fakten

π is irrational

Circle area uses Math.PI (≈ 3.141592653589793). Display rounds; engineering tolerances may need more digits.

Height must be perpendicular

Triangle “height” is the altitude to the chosen base — not a slanted side length.

Heron needs a valid triangle

Sides 2, 3, 9 cannot form a triangle; the calculator hides the result instead of inventing an area.

m² ↔ ft²

1 m² ≈ 10.7639 ft² using the international foot (0.3048 m exactly).

Composite shapes

Split L-shapes into rectangles (or mix shapes), compute each area, then add or subtract cut-outs.

Häufig gestellte Fragen

Kreis wählen, Radius eingeben. Fläche = πr².

Mit Seiten a, b, c: s = (a+b+c)/2, Fläche = √[s(s−a)(s−b)(s−c)].

Nein — ein Einheitensystem wählen.

In Rechtecke zerlegen (oder Formen mischen), jede Fläche berechnen und addieren. Ausschnitte genauso abziehen.

Quellen

  1. SI units — metre — National Institute of Standards and Technology (NIST) SI length basis for area units.
  2. International foot — NIST International foot = 0.3048 m exactly.
  3. Heron’s formula — Encyclopaedia Britannica Classical formula for triangle area from three sides.