What formula is used to find the angle between two vectors?

The angle theta between two vectors A and B is found using the dot product formula: cos(theta) = (A dot B) / (|A| times |B|), where A dot B is the dot product of the vectors and |A| and |B| are their magnitudes (lengths). Solving for theta gives: theta = arccos((A dot B) / (|A| times |B|)). This formula works for both 2D and 3D vectors and always returns an angle between 0 and 180 degrees.

What does it mean if the angle between two vectors is 90 degrees?

If the angle between two vectors is exactly 90 degrees, the vectors are perpendicular (also called orthogonal). This happens when their dot product equals zero. For example, the vectors (1, 0) and (0, 1) are perpendicular because 1 times 0 plus 0 times 1 equals 0. Perpendicular vectors are important in physics, engineering, and mathematics because forces or components at right angles to each other do not influence one another along the perpendicular direction.

What is the difference between the angle in degrees and radians?

Degrees and radians are two units for measuring angles. A full circle is 360 degrees or 2 pi radians. To convert degrees to radians, multiply by pi divided by 180. To convert radians to degrees, multiply by 180 divided by pi. For example, 90 degrees equals pi divided by 2 radians (approximately 1.5708 radians). Scientific calculators and most programming languages use radians by default, while degrees are more familiar for everyday use.

Angle Between Two Vectors Calculator

Find the angle between two vectors in 2D or 3D space. Enter the components of each vector and this calculator uses the dot product formula to return the angle in both degrees and radians, along with the dot product and magnitudes.

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Standard formula Dot product method: theta = arccos((A · B) / (|A| × |B|)).

1. Dimensions

Vector dimensions

2. Vector A

a_x

a_y

a_z

3. Vector B

b_x

b_y

b_z

One or more vectors has zero magnitude. The angle is undefined when a vector has no length.

Angle Between the Vectors

Angle (Degrees)
-
degrees

Angle (Radians)

rad

Dot Product

A · B

Relationship

vector orientation

Working

Dot product (A · B)-

Magnitude |A|-

Magnitude |B|-

|A| × |B|-

cos(theta) = dot / (|A||B|)-

theta = arccos(cos theta)-

Vector Properties

Vector A components-

Vector B components-

|A| (magnitude of A)-

|B| (magnitude of B)-

Unit vector same direction?-

Angle-

Result: Enter vector components above to calculate the angle.

How to Find the Angle Between Two Vectors

The angle between two vectors is found using the dot product formula. For vectors A and B, the formula is:

theta = arccos( (A · B) / (|A| × |B|) )

where A · B is the dot product and |A| and |B| are the magnitudes of the vectors. The result is always between 0 and 180 degrees (0 and pi radians).

Step-by-Step Method (3D Example)

For vectors A = (1, 2, 3) and B = (4, 5, 6):

Step	Calculation	Result
Dot product	(1×4) + (2×5) + (3×6)	4 + 10 + 18 = 32
Magnitude \|A\|	sqrt(1² + 2² + 3²) = sqrt(14)	3.7417
Magnitude \|B\|	sqrt(4² + 5² + 6²) = sqrt(77)	8.7750
Product \|A\|×\|B\|	3.7417 × 8.7750	32.8327
cos(theta)	32 / 32.8327	0.97463
Angle theta	arccos(0.97463)	12.93 degrees (0.2257 rad)

This matches the calculator default output above.

Dot Product Formula

For 2D vectors A = (a_x, a_y) and B = (b_x, b_y):

A · B = a_xb_x + a_yb_y

For 3D vectors A = (a_x, a_y, a_z) and B = (b_x, b_y, b_z):

A · B = a_xb_x + a_yb_y + a_zb_z

Special Cases

Angle	Dot Product	Relationship
0 degrees	Positive maximum (= \|A\|\|B\|)	Parallel (same direction)
90 degrees	0	Perpendicular (orthogonal)
180 degrees	Negative maximum (= -\|A\|\|B\|)	Anti-parallel (opposite directions)

2D Example

For vectors A = (3, 4) and B = (1, 0):

A · B = 3×1 + 4×0 = 3. |A| = sqrt(9+16) = 5. |B| = 1. cos(theta) = 3/5 = 0.6. theta = arccos(0.6) = 53.13 degrees.

Applications

The angle between vectors is used in physics (force components, work = F·d×cos(theta)), computer graphics (lighting calculations, surface normals), machine learning (cosine similarity between document vectors), and engineering (structural analysis, navigation).

Related Calculators

Maths and Stats Calculators: full collection of maths tools.
Dot Product Calculator: compute A · B for 2D and 3D vectors.
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Triangle Calculator: solve any triangle from sides and angles.
Pythagorean Theorem Calculator: find the hypotenuse or a missing side.

Sources and method: Dot product and angle formula from standard linear algebra. Anton, H. and Rorres, C. (2014). Elementary Linear Algebra. 11th ed. Wiley. Stewart, J. (2015). Calculus. 8th ed. Cengage. Formula: theta = arccos((A · B) / (|A||B|)) where the result is in the range [0, pi] radians.

This calculator computes the angle between two vectors using exact floating-point arithmetic. Results are rounded to four decimal places for display. The formula is valid for any non-zero vectors in 2D or 3D space. If either vector has zero magnitude, the angle is mathematically undefined.

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