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Math

Vector Cross Product Calculator (3D)

Enter two 3D vectors a = ⟨a_x, a_y, a_z⟩ and b = ⟨b_x, b_y, b_z⟩. The tool applies a × b = ⟨a_y b_z − a_z b_y, a_z b_x − a_x b_z, a_x b_y − a_y b_x⟩, then reports the magnitude |a × b| = |a|·|b|·sin θ, the parallelogram area, the triangle area (½·|a × b|) and the angle θ between the inputs. Physics torque, surface normals in 3D graphics and CCW orientation tests in computational geometry all run off the same formula — one calculation, three answers.

Vector A (3D)
Vector B (3D)

Cross product a × b

⟨0, 0, 1⟩

|a × b|

1

sin θ

1

Angle θ

90°

Parallelogram area

1

Triangle area (½·|a × b|)

0.5

Formula: a × b = ⟨a_y b_z − a_z b_y, a_z b_x − a_x b_z, a_x b_y − a_y b_x⟩; |a × b| = |a|·|b|·sin θ equals the parallelogram area. The direction follows the right-hand rule. The URL remembers ax, ay, az, bx, by, bz.

Formula

a × b = ⟨a_y b_z − a_z b_y, a_z b_x − a_x b_z, a_x b_y − a_y b_x⟩ |a × b| = |a| · |b| · sin θ ⇒ sin θ = |a × b| / (|a|·|b|) Parallelogram area = |a × b| Triangle area = ½·|a × b|

Frequently asked

What is the difference between the cross product and the dot product?

Both operate on two vectors but produce different things. The dot product a · b is a scalar built from cos θ; the cross product a × b is a vector (in 3D) built from sin θ, pointing perpendicular to both inputs. Dot measures alignment (max at θ = 0°); cross measures perpendicularity (max at θ = 90°). Use a · b = 0 to test orthogonality; use a × b for surface normals and torque. They are linked by the Lagrange identity |a × b|² + (a · b)² = |a|² · |b|².

Why is the cross product only defined in 3D?

A cross product wants to take two input vectors and return a single perpendicular direction (up to sign). In n-dimensional space the orthogonal complement of two vectors has dimension n − 2 — that is 1-dimensional only when n = 3, so only there is the direction unique. In other dimensions the natural generalisation is the wedge product a ∧ b, whose output is a 2-form (a bivector), not a 1D vector. (As a curiosity, a genuine vector cross product also exists in 7D, but it is an exotic algebraic structure and almost never used.)

How do I use the cross product to find a 3D triangle area?

Given three vertices P, Q, R, take the edge vectors u = Q − P and v = R − P; the triangle area is ½·|u × v|. This tool already reports ½·|a × b|, so feed u and v into the A and B fields. Heron's formula also works but the cross-product route avoids computing a semi-perimeter and yields the surface normal direction as a bonus — useful when you also want the plane equation or an incidence angle.

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