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MachineCalcs

Cylindricity & Runout (TIR) Calculator

GD&T runout from total indicator reading (TIR = max − min) with a pass/fail check, plus the cylindricity form zone from the measured diameter spread. Metric and imperial.

Inputs

mm
mm
mm
mm
mm

Results

Runout (TIR) ✓
0.04 mm

Within tolerance.

Max reading − min reading (full indicator movement).

Cylindricity zone
0.02 mm

(max Ø − min Ø) ÷ 2

  • Runout (TIR) is the total indicator reading: the full sweep of the indicator, max − min, as the part turns about its datum axis.
  • Cylindricity is a form control — the radial band (max radius − min radius) containing the whole surface, independent of any datum: (max Ø − min Ø) ÷ 2.

How it works

Runout (TIR) is the total indicator reading — the full sweep of the indicator about the datum axis as the part rotates: TIR = max reading − min reading A single dial indicator captures both form and location error in one number, which is why runout is one of the easiest GD&T controls to inspect on a lathe or between centers.

Cylindricity is a form control — the radial band (max radius − min radius) that contains the entire surface, independent of any datum: zone = (max Ø − min Ø) ÷ 2 Because it constrains the surface to lie between two coaxial cylinders, the zone is a radial width, so the diameter spread is halved.

Worked example

A part is rotated about its datum axis and the indicator swings from −0.01 mm to +0.03 mm, so the runout is 0.03 − (−0.01) = 0.04 mm — within a 0.05 mm tolerance, so it passes. Measuring the surface over its length gives diameters from 24.98 mm to 25.02 mm, so the cylindricity zone is (25.02 − 24.98) ÷ 2 = 0.02 mm. The calculator shows exactly this.

Frequently asked questions

How do you calculate runout (TIR)?
Runout is the total indicator reading: TIR = max reading − min reading. Rest a dial indicator on the surface, rotate the part one full turn about its datum axis, and the full indicator movement (highest minus lowest reading) is the runout.
What is the difference between circular and total runout?
Circular runout is the indicator sweep at a single cross-section as the part turns. Total runout moves the indicator along the whole length while it rotates, controlling the entire surface at once. Both are read as max − min; total runout is the stricter control.
What is cylindricity?
Cylindricity is a form control: a radial zone between two coaxial cylinders that contains the whole surface. The zone width is the max radius − min radius, i.e. (max diameter − min diameter) ÷ 2. Unlike runout it references no datum.
How is runout different from concentricity?
Runout measures the surface sweep with a single indicator and captures both form and location error in one reading. Concentricity controls the derived median points (the axis) relative to a datum and is far harder to measure — most drawings use runout or position instead.
How do I measure runout with a dial indicator?
Mount the part between centers or in a chuck on its datum axis, zero a dial indicator against the surface, and rotate one full turn. Record the highest and lowest readings; their difference is the runout (TIR). For total runout, traverse the indicator along the length as you rotate.
Does this work in metric and imperial?
Yes — toggle SI/imperial anytime; indicator readings, diameters, and the resulting zones all convert.

Method & assumptions

  • Runout assumes the part is rotated about its datum axis (between centers or on a true datum); the TIR is the full indicator movement over one rotation.
  • Cylindricity uses the radial half of the measured diameter spread — the zone between two coaxial cylinders, referencing no datum.
  • A CMM that fits a least-squares or minimum-zone cylinder may report slightly different values than a dial-indicator sweep, which captures the worst-case spread.

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