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Cosine Calculator

Calculate the cosine of any angle in degrees or radians. Returns values between -1 and 1.

Reviewed by Chase FloiedUpdated

This free online cosine calculator provides instant results with no signup required. All calculations run directly in your browser — your data is never sent to a server. Enter your values below and see results update in real time as you type. Perfect for everyday calculations, homework, or professional use.

Results

cos(θ)

0.5

Angle (radians)

1.047198 rad

How to Use This Calculator

1

Enter your input values

Fill in all required input fields for the Cosine Calculator. Most fields include unit selectors so you can work in your preferred unit system — metric or imperial, whichever matches your problem.

2

Review your inputs

Double-check that all values are correct and that you have selected the right units for each field. Incorrect units are the most common source of calculation errors and can produce results that are off by factors of 2, 10, or more.

3

Read the results

The Cosine Calculator instantly computes the output and displays results with units clearly labeled. All calculations happen in your browser — no loading time and no data sent to a server.

4

Explore parameter sensitivity

Try adjusting individual input values to see how the output changes. This is a quick and effective way to develop intuition about how different parameters influence the result and to identify which inputs have the largest effect.

Formula Reference

Cosine Calculator Formula

See calculator inputs for the governing equation

Variables: All variables and their units are labeled in the calculator interface above. Input fields accept values in multiple unit systems — select your preferred unit from the dropdown next to each field.

When to Use This Calculator

  • •Use the Cosine Calculator when you need a quick mathematical result without writing out all the steps manually, saving time on repetitive calculations.
  • •Use it to verify hand calculations on tests or assignments and catch arithmetic mistakes.
  • •Use it when teaching or explaining mathematical concepts to others, demonstrating how changing inputs affects the result.
  • •Use it to explore the behavior of mathematical functions across a range of inputs.

About This Calculator

The Cosine Calculator is a free mathematical calculation tool for students, educators, and professionals who need quick, reliable results. Calculate the cosine of any angle in degrees or radians. Returns values between -1 and 1. The underlying algorithms implement well-established mathematical formulas and numerical methods. Results are computed instantly in the browser. This tool is useful for learning, verification of hand calculations, and rapid exploration of mathematical relationships. All computation happens locally — no data is sent to a server.

About Cosine Calculator

The cosine function is the second primary trigonometric function, complementary to sine. In a right triangle, cos(θ) equals the ratio of the side adjacent to angle θ to the hypotenuse. On the unit circle, cos(θ) is the x-coordinate of the point at angle θ. Like sine, cosine oscillates between −1 and 1 with a period of 360°, but it is an even function: cos(−θ) = cos(θ). Cosine is phase-shifted 90° from sine: cos(θ) = sin(θ + 90°). It appears throughout physics in the dot product formula, work calculations (W = Fd cos θ), projection formulas, and Fourier analysis. Key values include cos(0°) = 1, cos(30°) = √3/2, cos(45°) = √2/2, cos(60°) = 0.5, and cos(90°) = 0. This calculator computes cosine for any angle.

The Math Behind It

Cosine can be defined as the x-coordinate on the unit circle, the real part of e^(iθ), or via the Taylor series cos(x) = 1 − x²/2! + x⁴/4! − x⁶/6! + .... The derivative is d/dx cos(x) = −sin(x), and the integral is ∫ cos(x) dx = sin(x) + C. Cosine satisfies the same differential equation as sine: y'' + y = 0. The cosine function is even (symmetric about the y-axis), while sine is odd. The dot product of two vectors a·b = |a||b|cos(θ) uses cosine to measure alignment: cos(0°) = 1 (parallel), cos(90°) = 0 (perpendicular), cos(180°) = −1 (anti-parallel). The discrete cosine transform (DCT), which uses only cosine basis functions, is the mathematical foundation of JPEG image compression and MP3 audio compression. The cosine rule in probability gives the angle between random variables. In the Fourier series, cosine terms capture the even (symmetric) components of periodic functions.

Formula Reference

Cosine Function

cos(θ) = adjacent / hypotenuse

Variables: θ = angle (in a right triangle)

Worked Examples

Example 1: Work done by a force

A 100 N force is applied at 30° to the direction of motion over 5 m.

Step 1:W = F × d × cos(θ)
Step 2:W = 100 × 5 × cos(30°)
Step 3:W = 500 × 0.8660

W ≈ 433 Joules

Common Mistakes & Tips

  • !Confusing cos(θ) with sin(θ) — remember cos uses the adjacent side, not the opposite.
  • !Forgetting that cos(90°) = 0, not 1.
  • !Assuming cos(A + B) = cos(A) + cos(B) — the correct formula involves products.

Related Concepts

Sine Calculator

The complementary trig function: sin(θ).

Arccos Calculator

Find the angle from a cosine value.

Used in These Calculators

Calculators that build on or apply the concepts from this page:

Arccos Calculator (Inverse Cosine)

Phase Shift Calculator

Secant Calculator

Sine Calculator

Frequently Asked Questions

Is cos(θ) = sin(90° − θ)?

Yes. This co-function identity shows that cosine and sine are complementary: cos(θ) = sin(90° − θ).

When is cosine negative?

Cosine is negative in Quadrants II (90° to 180°) and III (180° to 270°).