Type a point in any system and the other two update instantly, with the point drawn in 3D and its radius and angles traced out so you can see what each number means. Switch between the physics (ISO) and maths angle conventions, degrees or radians, and get the distance and midpoint to a second point.
Cylindrical (ρ, φ, z): ρ = √(x² + y²), φ = atan2(y, x), z unchanged. Back: x = ρ cos φ, y = ρ sin φ.
Spherical (r, θ, φ) in the physics/ISO convention: r = √(x² + y² + z²), polar angle from +z θ = acos(z / r), azimuth φ = atan2(y, x). Back: x = r sin θ cos φ, y = r sin θ sin φ, z = r cos θ. Many maths textbooks swap the names θ and φ — pick the convention that matches your course.
Elevation (used in navigation and astronomy) is 90° − θ. Distance between points is √(Δx² + Δy² + Δz²).
Worked example: (1, 1, √2) → r = 2, θ = 45°, φ = 45°; cylindrical ρ = √2 ≈ 1.414, φ = 45°, z ≈ 1.414.