◒Plane Geometry Calculator

Analyse essential 2D shapes with formulas, measurements, interactive visuals, and clear step-by-step working.

Triangle From Three Side Lengths

Returns validity, perimeter, Heron area, all angles, side and angle classification, inradius, circumradius, and altitude.

Steps
Classic Examples
Triangle3–4–5 right triangleTriangle5–6–7 scaleneRight Trianglefind hypotenuseRight Trianglehypotenuse and angleCircleradius fiveSectorquarter circleRectangle3–4–5 diagonalTrapezoidbases 12 and 6Polygonregular hexagonPolygonregular pentagonRhombus10 by 8 diagonalsRhombussquare diagonal case
Steps Modes
None  Answer and diagram only.
Summary  Methods as compact pills.
Detailed  Openable calculation steps with substitutions.
Operations Guide
△ABC — Triangle
Heron area, angles, radii, classification
a²+b² — Right Triangle
Sides, acute angles, altitude
πr² — Circle
Diameter, circumference, area
θ° — Sector
Area, arc, chord, perimeter
l×w — Rectangle
Area, perimeter, diagonal
a∥b — Trapezoid
Equal legs, area, base angles
n-gon — Regular Polygon
Angles, apothem, diagonals
◇ — Rhombus
Diagonal-based measurements
Key Formulas
Heron\(K=\sqrt{s(s-a)(s-b)(s-c)}\)
Pythagoras\(a^2+b^2=c^2\)
Circle\(A=\pi r^2\)
Sector\(L=\theta(2\pi r)/360\)
Rectangle\(d=\sqrt{l^2+w^2}\)
Trapezoid\(A=(a+b)h/2\)
Regular polygon\(A=ns^2/(4\tan(\pi/n))\)
Rhombus\(A=d_1d_2/2\)
Input Tips
  • Enter positive whole numbers or decimals.
  • All lengths use the same unit system.
  • Triangle sides must satisfy the triangle inequality.
  • Use 0° to 360° only for sector angles.
  • Regular polygons need whole-number side counts.
  • The trapezoid option assumes equal non-parallel sides.
  • Visuals resize around the calculated shape.
CalcPro Plane Geometry Calculator © 2026 · PHP Geometry Engine + Canvas Visuals + KaTeX

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