Law of Cosines Calculator

  • Enter the values for Side A, Side B, and Angle C.
  • Select the appropriate units for each value.
  • Click the "Calculate" button to perform the calculations.
  • View the results including Side C, Angle A, Angle B, Area, and Semiperimeter.
  • Copy the results to the clipboard using the "Copy Results" button.
  • Your calculation history is displayed below.

Side C:

Angle A:

Angle B:



Calculation Details:
Calculation History:

    The Law of Cosines Calculator is a valuable tool in the field of trigonometry that enables individuals to calculate the lengths of sides or angles of a triangle when they have limited information. This tool is essential for students, engineers, surveyors, and anyone working with triangles in various applications.

    The Concept of the Law of Cosines

    The Law of Cosines is a trigonometric formula used to find the lengths of the sides or the measures of the angles in a triangle. Unlike the Pythagorean theorem, which is applicable only to right triangles, the Law of Cosines is versatile and can be applied to any triangle, be it acute, obtuse, or right-angled.

    The formula for the Law of Cosines is as follows:

    c^2 = a^2 + b^2 – 2ab * cos(C)


    • c is the length of the side opposite angle C.
    • a and b are the lengths of the other two sides.
    • C is the measure of angle C in the triangle.

    This formula allows us to calculate the missing side or angle in a triangle when we know the lengths of two sides and the included angle or when we know all three sides of the triangle.

    Related Formulae

    Law of Sines

    The Law of Sines is another important trigonometric formula used in solving triangles. It relates the lengths of the sides of a triangle to the sines of its angles. The formula is as follows:

    a / sin(A) = b / sin(B) = c / sin(C)


    • a, b, and c are the lengths of the sides of the triangle.
    • A, B, and C are the measures of the angles opposite to sides a, b, and c, respectively.

    The Law of Sines is particularly useful when we have limited information about a triangle and need to find missing angles or sides.

    Pythagorean Theorem

    Although the Law of Cosines is more versatile, the Pythagorean Theorem remains a fundamental concept in trigonometry. It is used to find the length of the hypotenuse in a right triangle. The formula is:

    c^2 = a^2 + b^2


    • c is the length of the hypotenuse.
    • a and b are the lengths of the other two sides.

    Benefits of the Law of Cosines Calculator

    The Law of Cosines Calculator offers several benefits for individuals dealing with triangles and trigonometry:

    1. Versatility

    One of the key advantages of the Law of Cosines is its versatility. It can be applied to all types of triangles, including acute, obtuse, and right-angled triangles, making it a valuable tool in various fields such as engineering, physics, navigation, and surveying.

    2. Solving Real-World Problems

    Engineers and surveyors frequently use the Law of Cosines to solve real-world problems. For example, it can be used to calculate distances between points on the Earth’s surface, determine the height of a mountain, or find the length of a diagonal brace in a truss structure.

    3. Academic Applications

    In an educational context, the Law of Cosines Calculator aids students in understanding and practicing trigonometric concepts. It provides a practical way to solve triangles and reinforces the principles of trigonometry.

    4. Time and Effort Savings

    The calculator eliminates the need for manual calculations, which can be time-consuming and error-prone, especially when dealing with complex triangles. It allows for quick and accurate results, saving both time and effort.

    5. Accessibility

    The Law of Cosines Calculator is readily available online, making it accessible to anyone with an internet connection. Users can easily input their triangle’s data and obtain the desired results, enhancing convenience and efficiency.

    Interesting Facts

    Here are some interesting facts related to the Law of Cosines and its historical significance:

    1. Ancient Origins

    The Law of Cosines has ancient origins and can be traced back to Indian and Greek mathematicians. It was independently discovered by Indian mathematician Brahmagupta and Greek mathematician Ptolemy in the 7th century AD. This demonstrates the universality of mathematical principles across different cultures and time periods.

    2. Navigational Use

    In the past, sailors and navigators used the Law of Cosines to determine their ship’s position at sea. By measuring the angles between celestial objects, such as the Sun and stars, and knowing the lengths of certain sides of a spherical triangle, they could calculate their latitude and longitude, aiding in safe navigation.

    3. Astronomical Applications

    Astronomers have also utilized the Law of Cosines in their calculations, particularly when studying the positions and movements of celestial bodies. It plays a role in celestial navigation and determining the angles between planets and stars.


    The Law of Cosines Calculator is a versatile and invaluable tool in the world of trigonometry. Its ability to solve triangles of any type, coupled with its real-world applications, makes it a fundamental resource for students and professionals alike. Understanding the concept of the Law of Cosines, related formulae, and its historical significance enriches our appreciation for the role of mathematics in diverse fields.

    Whether used for solving practical problems or educational purposes, the Law of Cosines Calculator continues to play a vital role in simplifying complex trigonometric calculations.

    Last Updated : 19 January, 2024

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