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Engineering Kit

Triangle calculator and solver

A free online triangle calculator and triangle solver. Move the three sides and the triangle redraws with its heights, so you can see the shape the numbers describe, and see immediately when three lengths cannot close into a triangle at all.

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Triangle schematic with sides a, b and c, angles A, B and C, and the height dropped onto the base.

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Drive the inputs and watch the geometry redraw in real time. The preview deliberately stops short of the numbers: the remaining sides and angles, perimeter, area and all three heights all stay in the Android app.

Triangle solver demo

Set the three sides and watch the triangle and its heights redraw, including the cases that cannot close.

180 mm
140 mm
110 mm

The three sides have to satisfy the triangle inequality. Push them past it and the drawing tells you the set cannot close.

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What the triangle calculator & solver works out

Triangle Calculator is deliberately narrow: it solves one sizing problem completely, with the assumptions written down next to the result.

Remaining sides and angles
from three sides, two sides and an angle, or one side and its adjacent angles.
Area
by Heron's formula, or from two sides and the included angle.
Perimeter
with every side in the unit you are working in.
All three heights
the altitude onto each side, drawn on the triangle.
Degrees or radians
angles reported either way.

Typical jobs

100% offline

Triangle Calculator for Android

The Android app solves the triangle numerically from any valid input set, reports the sides, angles, perimeter, area and the three heights, and draws the triangle with its altitudes, offline. No account, no sign-in, no data connection.

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