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Inscribed Circle Calculator

Inradius r = K/s, incentre, tangent points and incircle of a triangle, from three sides or three vertices, with the figure drawn.

Related tools

All Geometry tools →
Circumscribed Circle CalculatorCircumradius R = abc/4K, circumcentre and circumcircle of a triangle, from three sides or three vertices, with the figure drawn.Great Circle Distance CalculatorGreat-circle distance between two latitude/longitude points by the haversine formula, with initial and final bearing, the midpoint and a globe view.Circle calculatorCompute the area, circumference and diameter of a circle from its radius.Circle sector area calculatorCompute the area and arc length of a circle sector from its radius and angle.Tangent Line to Circle CalculatorThe tangent lines from a point to a circle, with the tangent length and a live diagram.Interactive Unit Circle VisualizerDrag around the circle and watch all six functions move with the angle, in degrees and radians. Special angles give their exact values — √3/2, not 0.866 — the quadrant signs are named, and tan at 90° says undefined instead of printing a huge number.3D Distance CalculatorCompute the distance between two points in space, with an isometric view, the Δx / Δy / Δz components and the midpoint.Angle Bisector Calculator (triangle)Enter the three sides or the three vertices and get the length of each internal angle bisector, the incenter, the inradius, and the exact point where every bisector cuts the opposite side. The angle bisector theorem is the heart of it: the bisector splits the opposite side in the ratio of the two adjacent sides. The triangle inequality is checked before anything is computed, and the triangle is drawn with its three bisectors.

Open Inscribed Circle Calculator and you get an answer straight away, with no account to create. You will find it under Geometry, with Circumscribed Circle Calculator and Great Circle Distance Calculator for the neighbouring cases.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What does Inscribed Circle Calculator do?

Inradius r = K/s, incentre, tangent points and incircle of a triangle, from three sides or three vertices, with the figure drawn.

When would I actually use this?

Homework and site work alike: how much paint a wall takes, how much water a tank holds, whether a corner is square — and, on the coordinate side, the slope between two points, the distance across a plan, the midpoint of a span.

What is the most common mistake?

Mixing units inside one shape. Entering a length in centimetres and a width in metres gives an area wrong by a factor of a hundred, and the result looks perfectly plausible.

How is Inscribed Circle Calculator different from Circumscribed Circle Calculator?

They sit next to each other but answer different questions: Circumscribed Circle Calculator is the one to open when you need it to circumradius R = abc/4K, circumcentre and circumcircle of a triangle, from three sides or three vertices, with the figure drawn. Pick whichever matches what you're starting from — both are free.

Is there a tool for the next step?

Great Circle Distance Calculator is the closest one after this: Great-circle distance between two latitude/longitude points by the haversine formula, with initial and final bearing, the midpoint and a globe view.

What else is worth having open alongside it?

Circle calculator and Circle sector area calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

The formulas are the classical ones and the results are exact to the precision shown — geometry does not change with the year or the country, so nothing here needs updating.

Further reading

All guides →
How-toCircle: Circumference and AreaCircumference is 2πr, area is πr². Here's how radius, diameter and π fit together, both formulas worked through, and how not to mix them up.ExplainerThe Pythagorean Theorem ExplainedIn a right triangle, a² + b² = c². Here's what the formula means, a worked example, how to find any side, and where it's used in real life.How-toHow to Calculate VolumeVolume is the space inside a shape. Here's how to find it for boxes, cylinders and spheres, and why keeping your units consistent is the whole game.ExplainerThe Flat Pattern of a Cone Is a Sector, Not a CircleRoll a 50 mm cone 80 mm tall and its pattern is a 190.8° slice of a 94 mm circle. Flatten a nearly cylindrical lampshade and the pattern radius runs to 839 mm — the shallower the taper, the further away the apex.How-toHow to Find the Distance Between Two PointsUse the distance formula d = √((x₂−x₁)² + (y₂−y₁)²) to measure the straight-line distance between two points on a plane, with a worked example and the midpoint too.How-toHow to Calculate the Slope of a Line: Rise Over RunFind the slope of a line from two points with m = (y₂ − y₁) / (x₂ − x₁), and read what a positive, negative, zero, or undefined slope tells you.
Inscribed Circle Calculator — OneKitly