AtlasCalcsUtility Calculation Suite
2026-07-30 8 min

Circular Runout Calculator

Calculate circular runout (FIM) from per-revolution readings. Evaluate rotational accuracy of cylindrical parts against tolerance limits per ASME Y14.5.

Calculator

Unit System
Readings per Revolution (mm)
Datum Axis
Rotational Speed (rpm)
Tolerance Value (mm)

Results

Optimal

Circular Runout (FIM)

0.0300mm

Full indicator movement - max radial variation per revolution

Full Indicator Movement

0.0300mm

Difference between max and min readings

Average Deviation

0.0225mm

Mean of all readings per revolution

Deviation Ratio

0.6000

Circular runout divided by tolerance value

Maximum Reading

0.0400mm

Highest indicator reading

Minimum Reading

0.0100mm

Lowest indicator reading

Number of Readings

8-

Count of readings analyzed

Visualizations

Results Overview

0mmCircular Runout
0mmFull Indicator Movement
0mmAverage Deviation
0.6mmDeviation Ratio
0mmMaximum Reading
0mmMinimum Reading
8mmNumber of Readings

Formula

Circular runout (also called Full Indicator Movement or FIM) is the total radial variation measured by a dial indicator as the part rotates one full revolution about the datum axis.

Circular_Runout = FIM = max(readings) - min(readings)

Alternative Form

Deviation_Ratio = Circular_Runout / Tolerance_Value

Variables

SymbolNameUnitDescription
readings[i]Indicator Reading at Position immRadial displacement reading at each angular position
FIMFull Indicator MovementmmTotal radial variation per revolution
DRDeviation Ratio-Ratio of measured runout to allowable tolerance

Explanation

Circular runout is a composite tolerance that controls the variation of a circular feature when rotated 360° about a datum axis. It simultaneously controls roundness and coaxiality at each individual circular cross-section. The measurement is performed with a dial indicator applied perpendicular to the surface while the part rotates.

Derivation

For each revolution, the indicator records the radial displacement at multiple equally-spaced positions. The Full Indicator Movement (FIM) is the algebraic difference between the maximum and minimum readings. Circular runout equals the FIM value. The deviation ratio compares the measured value to the specified tolerance - a ratio ≤ 1.0 indicates conformance.

Step-by-Step Calculation

Follow each step to understand how the result is calculated from your inputs.

Step 1

Mount the part on centers or a precision rotating fixture aligned to the datum axis.

Datum Axis:A (main shaft axis)
Rotational Speed:60 rpm
Result: Part aligned for measurement
Step 2

Position dial indicator perpendicular to the surface at the measurement cross-section.

Indicator Type:Dial indicator or LVDT
Resolution:0.001 mm typical
Result: Indicator zeroed at starting position
Step 3

Record 8 equally-spaced readings over one full revolution.

FIM = max(readings) - min(readings)
Max Reading:0.0400 mm
Min Reading:0.0100 mm
Intermediate: FIM = 0.0400 - 0.0100
Result: Circular Runout = 0.0300 mm
Step 4

Compare measured runout against the tolerance specification.

Deviation Ratio = Circular Runout / Tolerance
Measured:0.0300 mm
Tolerance:0.0500 mm
Result: PASS - Within tolerance
Final Answer
0.0300

Worked Examples

See how the calculator works with different scenarios.

Scenario

A precision ground shaft with specified circular runout of 0.05 mm to datum A. Readings: 0.02, 0.03, 0.01, 0.04, 0.02, 0.03, 0.01, 0.02 mm.

Inputs

Readings:0.02, 0.03, 0.01, 0.04, 0.02, 0.03, 0.01, 0.02 mm
Datum:A
Tolerance:0.05 mm

Calculation

FIM = 0.04 - 0.01 = 0.03 mm Circular Runout = 0.03 mm Deviation Ratio = 0.03/0.05 = 0.6

Result

Circular Runout: 0.0300 mm — PASS

Interpretation

The shaft meets the circular runout specification with a deviation ratio of 0.6, well within the 0.05 mm limit.

Understanding Your Result

Your Result: Circular Runout (FIM): 0.0300 mm

Typical range: Precision spindles: 0.002-0.010 mm. General machined shafts: 0.02-0.10 mm. Automotive: 0.01-0.05 mm. Heavy equipment: 0.05-0.20 mm.

What This Means

Circular runout quantifies the radial variation of a surface as it rotates about a datum axis. It is a composite control covering roundness, coaxiality, and surface irregularities at a specific cross-section.

Why It Matters

Excessive circular runout causes vibration, noise, bearing wear, and reduced service life in rotating machinery. It is critical for shafts, bearings, gears, and precision rotating assemblies.

Professional Interpretation

Circular runout is a production inspection test, not a design analysis. It detects manufacturing errors such as bent shafts, eccentric turning/grinding, misaligned centers, and out-of-round conditions. A passing result ensures the part will assemble and function correctly in rotation.

Recommendations

  • •Measure at multiple axial positions along the shaft to detect bent conditions
  • •Use at least 8 equally-spaced readings per revolution for reliable results
  • •Ensure the datum axis is properly established before measurement
  • •Clean the surface thoroughly before measurement to avoid debris affecting readings
  • •Use temperature-stable environments for precision measurements
  • •Verify indicator calibration before each use
  • •Repeat measurements at least 3 times and average the results

Educational Content

Introduction

Circular runout is a geometric dimensioning and tolerancing (GD&T) control defined by ASME Y14.5 and ISO 1101. It limits the amount of radial variation of a surface element when the part is rotated 360° about a datum axis.

Concept Explanation

The measurement principle is straightforward: a dial indicator contacts the surface perpendicularly while the part rotates. The indicator records the radial displacement throughout one complete revolution. Circular runout is the difference between the maximum and minimum readings, also known as Full Indicator Movement (FIM) or Total Indicator Reading (TIR).

Applications

▸Rotating shaft journals and bearing surfaces
▸Gear blanks and pulley mounting surfaces
▸Motor and generator armatures
▸Turbine and compressor rotors
▸Precision spindle assemblies
▸Automotive crankshafts and camshafts
▸Aerospace engine components

Benefits

  • •Quick and reliable production inspection method
  • •Detects multiple geometric errors simultaneously
  • •Low-cost measurement using standard dial indicators
  • •Internationally accepted per ASME and ISO standards
  • •Provides quantitative pass/fail criteria
  • •Applicable to both internal and external surfaces

Limitations

  • •Measures only at specific cross-sections (not along entire length)
  • •Cannot isolate individual error sources (roundness, coaxiality, surface finish)
  • •Requires accurate datum axis establishment
  • •Limited by indicator resolution and repeatability
  • •Does not measure total runout along the full surface

Best Practices

  • •Establish clear datum references on the drawing
  • •Use appropriate indicator resolution (1/10 of tolerance)
  • •Apply consistent contact pressure
  • •Record readings at uniform angular increments
  • •Perform measurements in temperature-controlled environments
  • •Document both readings and calculated results
  • •Use statistical process control to monitor trends

Common Misconceptions

Myth: Circular runout is the same as total runout.
Truth: Circular runout applies at individual cross-sections; total runout applies to the entire surface simultaneously.
Myth: A part with good roundness automatically has good runout.
Truth: A part can be perfectly round but have runout if its center is eccentric to the datum axis.
Myth: Circular runout can predict dynamic balance.
Truth: Runout and balance are related but different. A part with zero runout can still be unbalanced due to mass distribution.

Practical Tips

  • •Always zero the indicator at the lowest reading position, not the starting position
  • •Use a precision rotary table or between-centers fixture for datum establishment
  • •Take additional readings if any single reading seems anomalous
  • •Record the angular position of maximum reading for process correction guidance
  • •For thin-walled parts, consider the effect of clamping distortion on runout readings
  • •Use electronic indicators with data logging for statistical analysis
  • •Apply light contact force to avoid surface marring on finished parts

Common Mistakes

Using too few readings per revolution
Use at least 8 equally-spaced readings. More readings (12-24) provide better accuracy for irregular surfaces.
Not establishing the datum axis correctly
Use precision centers, a rotating table, or V-blocks to establish the true datum axis.
Confusing circular runout with total runout
Circular runout = FIM at one cross-section. Total runout considers the entire surface along the axis.
Measuring on dirty or damaged surfaces
Clean the surface thoroughly and inspect for burrs, nicks, or debris before measuring.
Using an indicator with insufficient resolution
Use an indicator with resolution at least 10x better than the tolerance (e.g., 0.001 mm for 0.01 mm tolerance).

Assumptions

This calculator makes the following assumptions to provide estimates:

Rigid Part: The part is assumed rigid - no deflection under indicator contact force or clamping.
Ideal Rotation: Rotation is about the true datum axis without wobble or spindle error.
Perpendicular Indicator: The indicator is perfectly perpendicular to the surface at the measurement point.
Steady-State Temperature: The part and fixture are at thermal equilibrium during measurement.

Limitations

Be aware of these limitations when using this calculator:

Single Cross-Section: Circular runout is evaluated at individual cross-sections, not along the entire surface length.
Composite Error: Cannot distinguish between roundness error, eccentricity, and surface finish contributions.
Operator Dependent: Results can vary with operator technique, indicator placement, and contact force.
Datum Quality: The accuracy of results depends heavily on the quality of the datum axis establishment.

Frequently Asked Questions

Answers to common questions about this calculator.

What is circular runout?
Circular runout is a GD&T control that limits the radial variation of a surface element when the part is rotated 360° about a datum axis. It is measured as the Full Indicator Movement (FIM).
How is circular runout different from total runout?
Circular runout applies at individual cross-sections (one circle at a time), while total runout controls the entire surface simultaneously along the axis.
What is FIM in runout measurement?
Full Indicator Movement (FIM) is the algebraic difference between the maximum and minimum indicator readings during one full revolution. FIM equals circular runout.
How many readings are needed for circular runout?
At minimum 8 equally-spaced readings per revolution are recommended. For higher accuracy, use 12-24 readings, especially for surfaces with suspected lobing.
What causes circular runout?
Common causes include bent shafts, eccentric turning or grinding, misaligned centers, out-of-round conditions, uneven material removal, and assembly misalignment.
What is the difference between runout and roundness?
Roundness measures form deviation from a perfect circle. Runout includes both roundness error and eccentricity (center displacement relative to the datum axis).
How do I measure circular runout?
Mount the part on centers or a rotating fixture, apply a dial indicator perpendicular to the surface, rotate the part one revolution, and record the FIM.
What is a typical circular runout tolerance?
Precision components: 0.002-0.010 mm. General machining: 0.02-0.10 mm. Heavy equipment: 0.05-0.20 mm. Always check the specific drawing tolerance.
Can circular runout be measured on internal surfaces?
Yes, circular runout can be measured on both external (shafts) and internal (bores) surfaces using appropriate indicators and fixtures.
What standards govern circular runout?
ASME Y14.5 (Dimensioning and Tolerancing) and ISO 1101 (Geometrical Product Specifications) define circular runout controls.
How does temperature affect runout measurement?
Temperature changes cause thermal expansion, affecting both the part and fixture. Measure in temperature-controlled environments (20°C ± 1°C for precision work).
What indicator resolution do I need?
Use an indicator with resolution at least 10x the tolerance. For 0.01 mm tolerance, use 0.001 mm resolution. For 0.1 mm tolerance, 0.01 mm resolution is sufficient.
How do I interpret deviation ratio?
Deviation ratio = measured runout / tolerance. Ratio ≤ 1.0 means the part passes. Ratio > 1.0 means it exceeds tolerance. Ratios > 1.25 typically require rework.
What is the difference between shaft runout and bore runout?
Shaft (external) runout measures outer surface variation. Bore (internal) runout measures inner surface variation. The measurement principle is identical.
Can circular runout be checked on assembled components?
Yes, but ensure the assembly datum axis is clearly defined and the measurement conditions are repeatable.
What is the cost implication of tight runout tolerances?
Tighter runout tolerances increase manufacturing cost exponentially. A 0.005 mm tolerance may cost 3-5x more than 0.05 mm due to additional grinding/polishing operations.
How does surface finish affect runout readings?
Rough surfaces can cause erratic indicator readings. For accurate runout measurement, surface finish should be appropriate for the indicator contact tip.
What is the relationship between runout and vibration?
Excessive runout in rotating parts causes vibration at the rotational frequency. Runout of 0.025 mm can cause measurable vibration in high-speed spindles.
Can circular runout be predicted from manufacturing process?
Statistical process control (SPC) data from similar parts can predict expected runout. Machine tool accuracy, chucking methods, and material stability all affect runout.
How do I reduce circular runout in manufacturing?
Use between-centers machining, improve chucking accuracy, reduce cutting forces, stabilize material before final machining, and use balanced grinding wheels.
What is the difference between indicator resolution and accuracy?
Resolution is the smallest readable increment. Accuracy is the closeness to true value. A 0.001 mm resolution indicator may have ±0.002 mm accuracy.
How often should indicators be calibrated?
Dial indicators should be calibrated annually or per ISO 17025 requirements. More frequent calibration is needed for high-precision applications.
What is coaxiality and how is it related?
Coaxiality controls the alignment of two or more features to a common datum axis. Runout includes coaxiality error combined with form error.
Can circular runout be measured on non-cylindrical surfaces?
Circular runout typically applies to surfaces of revolution. Non-cylindrical surfaces use profile controls instead.
What is the difference between radial and axial runout?
Radial runout measures variation perpendicular to the axis. Axial (face) runout measures variation parallel to the axis on a face surface.
How do I measure runout on a lathe?
Mount a dial indicator on the toolpost, contact the rotating workpiece, and read the FIM as the lathe rotates the part at low RPM.
What is the lobing effect in roundness?
Lobing is a wavy surface with multiple peaks and valleys. Even-numbered lobes may not be detected by 2-point measurement but appear in runout checks.
How do soft materials affect runout measurement?
Soft materials may deform under indicator contact force, producing falsely low or erratic readings. Use low-force indicators for such materials.
What are the options for automated runout measurement?
Automated systems use laser sensors, LVDTs, or air gauges with motorized rotation and data acquisition software for statistical analysis.
How do I document circular runout results?
Record the datum reference, measurement position, tolerance value, FIM result, pass/fail status, and any relevant process notes. Use standard inspection report forms.
Can circular runout be applied to non-metallic parts?
Yes, as long as the surface is a feature of revolution. Plastics, composites, and ceramics can all be measured for circular runout.

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Glossary

Technical terms used in mortgage calculations explained in plain language.

ASME Y14.5
American Society of Mechanical Engineers standard for dimensioning and tolerancing, including GD&T symbols and rules.
Circular Runout
GD&T control limiting radial surface variation at any single cross-section when rotated about a datum axis.
Coaxiality
The condition where two or more features share a common axis of rotation.
Datum Axis
A theoretically exact axis established from datum features, used as the reference for runout measurement.
Dial Indicator
A mechanical or electronic measurement instrument with a contact tip that measures displacement against a graduated scale.
Eccentricity
The displacement of the geometric center of a feature from its true axis.
FIM
Full Indicator Movement - the total range of indicator readings during one revolution, equal to circular runout.
GD&T
Geometric Dimensioning and Tolerancing - a system for defining and communicating engineering tolerances.
Indicator Resolution
The smallest increment a measurement indicator can display, typically 0.001 mm or 0.0001 inch.
Roundness
A measure of how closely a cross-section approaches a perfect circle, independent of the center position.
Runout Tolerance
The allowable variation in surface position as a part rotates about a datum axis.
Total Runout
GD&T control applying runout simultaneously to the entire surface along the axis, not just individual cross-sections.

Authoritative References

Trusted sources and standards referenced by this calculator.

Applicable Standards

ASME Y14.5ISO 1101ISO 2768ASME B89.1.12ISO 1938ISO/TS 15530

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Page Information

Last Updated:

2026-07-30

Version:

2.0.0

License:

Free to use for educational and professional purposes.