Radius R
Two points and a radius normally produce two centres. G2/G3 plus the minor or major choice selects the intended solution.
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G2/G3 arc centre and I/J calculator
Find the centre, direction, radius, sweep and arc length. Verify the geometry in a preview and get an example ISO block.
Define with R or I/JMinor and major arcsG2/G3 code and previewLocal calculations
How it works
Two ways to define the same arc geometry.
Enter radius R or centre offsets I/J from the start point. The calculator checks whether the end point lies on the circle and blocks code generation for impossible geometry.
Centre offsets I/J
I is the X offset and J the Y offset from the arc start to its centre. This method can also define a full circle unambiguously.
Check before machining
The preview shows start, end, centre, chord and direction. Results also include arc length and estimated motion time.
G17 convention
G2 clockwise, G3 counter-clockwise — viewed from positive Z.
The generated example assumes absolute endpoint X/Y and incremental I/J from the arc start. Controls may use a different active arc-centre mode, so the code always requires verification.
FAQ
Common CNC arc questions
What are I and J in a G2/G3 block?
In the common incremental mode, I and J are the X and Y offsets from the arc start to its centre. The calculator also shows absolute centre coordinates.
How do I choose G2 or G3?
In G17, viewed from positive Z towards XY, G2 is clockwise and G3 is counter-clockwise.
Why are two arcs possible for one radius?
The same points and radius can form a minor arc up to 180° or a major arc above 180°. Direction and the selected solution determine the centre.
Can it calculate a full circle?
Yes. Use I/J with identical start and end points. Radius R alone does not identify the centre in that case.
Can I run the code without checking it?
No. Verify plane, direction, I/J mode, units, start position, control limits and a safe path on the specific machine.
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