Triangle Calculator
Calculate triangle side lengths, interior angles, area, perimeter, and geometric classifications from known measurements.
Run tool
The Triangle Calculator computes geometric properties for any solvable triangle from your supplied side and angle values. Enter known numeric measurements for sides A, B, and C, or specify angles A, B, and C in degrees. When you provide valid measurements, the tool calculates the missing lengths and interior angles, along with total perimeter, semiperimeter, and calculated area. It also determines the triangle classification based on side equality, identifying whether the figure is equilateral, isosceles, or scalene, as well as classification by angle type, such as acute, right, or obtuse. Length values are displayed rounded to four decimal places, and angle values are rounded to two decimal places. If you enter invalid dimensions that violate the triangle inequality, or enter angles whose total exceeds 180 degrees, the interface alerts you to adjust the inputs. This online tool offers a direct way to solve triangle geometry problems without manual trigonometry steps.
Instructions
- Enter known side lengths for Side A, Side B, or Side C as positive numbers.
- Enter known interior angle measurements in degrees for Angle A, Angle B, or Angle C.
- Submit the calculation to evaluate the triangle properties.
- View the resulting side lengths, angles, perimeter, semiperimeter, area, and classification labels in the result panel.
Examples
- Enter Side A = 3, Side B = 4, and Side C = 5 to calculate a right scalene triangle with an area of 6, perimeter of 12, semiperimeter of 6, and interior angles of approximately 36.87 degrees, 53.13 degrees, and 90.00 degrees.
- Enter Side A = 5, Side B = 5, and Side C = 5 to obtain an equilateral acute triangle with an area of approximately 10.8253, perimeter of 15, semiperimeter of 7.5, and all three angles equal to 60.00 degrees.
FAQ
What units should I use for triangle side lengths?
Side measurements are unitless numeric values. The resulting area and perimeter correspond to the same linear and square units you maintain across all inputs.
How are angle measurements interpreted?
All angle inputs and outputs are processed in degrees. The sum of the three interior angles in a valid flat triangle equals 180 degrees.
Why does the tool show an error for my inputs?
An error occurs if no positive values are supplied, if the sum of specified angles exceeds 180 degrees, or if three side lengths violate the triangle inequality where any two sides combined must exceed the third.
How are results rounded?
Calculated side lengths, perimeter, semiperimeter, and area are rounded to four decimal places. Interior angle measurements are rounded to two decimal places.