# Coordinate Geometry Calculator - Distance, Midpoint, Slope and Line Equations

> Free online coordinate geometry calculator: distance, midpoint, slope, line equations, point-to-line distance with the foot, triangle centres and polar form.

- URL: https://qilingtools.com/en/math/coordinate
- Category: Math Tools (https://qilingtools.com/en/math)
- Tags: [Math](https://qilingtools.com/en/tags/math), [Education](https://qilingtools.com/en/tags/education)
- Last updated: 2026-10-26
- Price: Free, no sign-up
- Privacy: Runs locally in the browser; files are never uploaded

The coordinate geometry you need most often: distance, midpoint, slope, line equations and the perpendicular bisector from two points; distance, foot of the perpendicular and reflection for a point and a line; area, collinearity, centroid and circumcircle for three points; plus conversion between polar and Cartesian coordinates.

## How to use

1. Choose two points, point and line, three points, or polar conversion
2. Enter the coordinates, or the A, B and C of the line
3. Read the results and the formula, and copy what you need

## Features

- Two points: distance, midpoint, slope, inclination, slope-intercept and general forms, perpendicular bisector
- Point and line: distance, foot of the perpendicular, reflection across the line
- Three points: area, collinearity, perimeter, centroid, circumcentre and circumradius
- Two-way polar ↔ Cartesian conversion in degrees and radians
- Vertical lines are flagged rather than given a bogus slope

## FAQ

### What is the distance formula?

d = √[(x₂−x₁)² + (y₂−y₁)²] — Pythagoras in coordinates. The midpoint is the average of each coordinate.

### How do I find the distance from a point to a line?

Write the line as Ax+By+C=0; then d = |Ax₀+By₀+C| / √(A²+B²). The foot of the perpendicular and the reflected point are given too.

### How can I tell whether three points are collinear?

Compute the triangle area — zero means collinear. The tool uses the cross product: S = ½|x₁(y₂−y₃) + x₂(y₃−y₁) + x₃(y₁−y₂)|.

### When is the slope undefined?

When the two points share an x-coordinate the line is vertical and has no slope; the equation is written x = constant and the tool says so explicitly.

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