Arc Radius Calculator (Chord & Height)

Inputs

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Straight distance between the two ends of the arc — a straightedge laid across the curve.
in
Sagitta: the gap from the middle of the straightedge to the arc, measured square to the chord.
in

Results

Default result
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Radius(r)
25.5in
Pass

Also computed

Diameter(d)51in

Arc height (sagitta)(h)3in

Included angle(θ)56.14°

Arc length(s)24.99in

Material length along the curve — what a roll or template consumes.

Method notes 4 notes
  • The bench version: lay a straightedge (chord) across the curve, measure the gap at its middle (rise), and r = c²/8h + h/2 — exact, not an approximation.
  • Three points define a circle: the formula is why a fragment of a broken flywheel or gasket is enough to recover the original diameter.
  • Shallow arcs amplify measurement error in the rise; long chords and indicator-grade height readings keep the answer honest.
  • Geometry only — springback for bent or rolled material is a process property and belongs to the bending data, not this screen.

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