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Triangle Calculator

Sides, angles, area and perimeter from any 3 values

Enter any 3 values (at least 1 side). Use degrees for angles. Leave others blank.

Formulas used

  • Law of cosines: c² = a² + b² − 2ab·cos(C) — solve for any side given two sides and included angle
  • Law of sines: a/sin(A) = b/sin(B) = c/sin(C) — find missing sides or angles
  • Heron's formula: Area = √(s(s−a)(s−b)(s−c)) where s = (a+b+c)/2
  • Angle sum: A + B + C = 180°

Triangle types

  • Equilateral: all sides equal, all angles 60°
  • Isosceles: two sides equal
  • Scalene: all sides different
  • Right: one 90° angle (a² + b² = c²)
  • Acute: all angles < 90°
  • Obtuse: one angle > 90°

User Reviews

Average 4.9 stars based on 8 user reviews.

Henry He2026-01-06
Role: Project Member

Our team runs into this during math result verification: quick conversions are easy to calculate with the wrong formula. Triangle Calculator keeps the triangle calculator flow short, and law of cosines helps with pre-handoff review for repeated Project Member work.

Nathan Ma2026-04-11
Role: Data Clerk

I needed triangle calculator that could finish unit conversion or math verification, not just a generic page. Triangle Calculator keeps law of cosines and heron formula close to the real workflow, and it saves time for teaching, office, and daily calculations.

Frank Xu2026-01-16
Role: Everyday User

For people searching triangle calculator for law of sines, this page matches the intent well. It is not a generic utility; Triangle Calculator is built around law of sines; frequent value changes are easy, and the result is easy to keep working with.

Lisa Li2026-04-21
Role: Office User

During daily conversion, Triangle Calculator solves the part I worry about most: quick conversions are easy to calculate with the wrong formula. By keeping SSS/SAS/ASA/AAS visible in the workflow, there is less manual cleanup, and it reduces manual conversion and repeated input, so it belongs in my regular tool list.

Jennifer Chen2026-01-26
Role: Developer

I would recommend Triangle Calculator to anyone who needs triangle calculator. It covers long-tail needs like triangle calculator for law of sines naturally, and features such as side a make the result easier to check than an ad hoc workaround.

Michelle Zhao2026-04-05
Role: Content Editor

The page focus is clear: the core is triangle calculator, law of sines, and quick office calculation. Triangle Calculator can quickly check whether the result looks right; the page is ready to use without extra setup, which makes it easy to judge before using it.

Linda Zhou2026-01-10
Role: Operator

When I need triangle calculator for law of sines, I care about fewer steps. Triangle Calculator keeps free online triangle calculator direct; with supports SSS, SAS, ASA, AAS and right triangles, follow-up review is easier for visitors coming from search.

Emily Lin2026-04-15
Role: Student

I found Triangle Calculator while looking for free online triangle calculator, and the real issue was that checking units and values across sources is slow. Supports SSS, SAS, ASA, AAS and right triangles and law of sines are on the same page, so I can finish unit conversion or math verification without stitching several tools together.