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Classifying Triangles Calculator.

Classify a valid triangle by side equality and by its angles.

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Set your values

Results update as you type.

Side classification: scalene

Side classification

scalene
Angle classification: right

Angle classification

right
Perimeter: 12 units

Perimeter

0.000000units
Area: 6 units²

Area

0.000000units²

Results update automatically as you type.

Use Cases

Check triangle type for geometry homework

Students can quickly verify if a triangle with given side lengths is equilateral, isosceles, or scalene, and whether it's acute, right, or obtuse.

Example: Enter sides 5, 5, 8 to see it's isosceles and acute.

Verify triangle properties for design or construction

Architects, engineers, or DIY enthusiasts can confirm the classification of a triangle from measured side lengths to ensure correct angles or symmetry.

Example: Enter sides 3, 4, 5 to confirm it's a right scalene triangle.

Frequently Asked Questions

How does the calculator classify a triangle?
It compares the three side lengths you enter. If all sides are equal, it's equilateral; if two are equal, isosceles; if none, scalene. It also checks the angles using the Pythagorean theorem to determine if the triangle is acute, right, or obtuse.
What if the sides don't form a valid triangle?
The calculator will indicate that the triangle is invalid. For a valid triangle, the sum of any two sides must be greater than the third side. If not, the sides cannot form a triangle.
Can I use any units for the side lengths?
Yes, you can enter side lengths in any consistent unit (e.g., inches, centimeters, meters). The classification is based on the ratios of the sides, so the unit doesn't affect the result.

Tips & Common Mistakes

Tips

  • Ensure all side lengths are positive numbers. Zero or negative values will not form a valid triangle.
  • Use the same unit for all three sides. Mixing units (e.g., inches and centimeters) will give incorrect results.
  • For a quick check, remember that if the sum of the two smaller sides is not greater than the largest side, the triangle is invalid.
  • The calculator classifies by both side equality and angle type, so you get a complete description like 'isosceles right triangle'.

Common Mistakes to Avoid

  • Entering side lengths that don't satisfy the triangle inequality (sum of any two sides > third side) and expecting a valid classification.
  • Using different units for different sides without converting, leading to incorrect side comparisons.
  • Assuming that a triangle with two equal sides is always acute; it could be right or obtuse depending on the side lengths.

Last updated: August 13, 2026