Quantify deviation from ideal circularity using maximum and minimum measured radius or diameter values, then compare the calculated roundness error with a specified limit.
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Roundness error is the deviation of an actual circular cross-section from an ideal circle. It is commonly called circularity error in engineering inspection.
For a simplified measurement approach, the variation between the maximum and minimum measured radial values can be used to quantify the radial roundness error. When diameter measurements are used, the maximum diameter minus the minimum diameter gives the corresponding diametral variation.
When measurements are recorded as radii, the simplified radial roundness error is the difference between the largest and smallest measured radius.
When measurements are recorded as diameters, the simplified diametral roundness error is the difference between the largest and smallest measured diameter.
This calculator keeps the selected measurement basis consistent with the entered tolerance.
Roundness and circularity are commonly used to describe the form of a circular feature. Unlike concentricity or runout, roundness is a form characteristic and does not require a datum axis for the basic circularity requirement.
A shaft can have good roundness while its axis is incorrectly positioned relative to another feature. Conversely, a feature can be correctly positioned but have poor circular form.
Roundness is important for shafts, journals and turned diameters where circular form affects bearing contact, sealing, rotation and fit.
Internal circular features can also be evaluated for roundness. Bore form can affect bearing fits, seals, bushings and mating cylindrical components.
Roundness controls the form of an individual circular cross-section. Runout is evaluated relative to a datum axis while the component rotates.
A component may have a small roundness error but still show significant runout if its circular feature is displaced from the datum axis.
Roundness describes the shape of one circular cross-section. Concentricity concerns the relationship between theoretical centers or axes of different circular features.
Therefore, diameter variation alone should not be interpreted as concentricity error.
A simplified roundness calculation requires the highest and lowest measured values from the inspected circular profile. The difference between these values quantifies the measured variation.
The accuracy of the result depends on how representative the measurement points are and on the capability of the inspection method.
Tolerance utilization shows how much of the specified roundness allowance is consumed by the calculated error.
For example, a measured roundness error of 0.04 mm against a 0.10 mm limit uses 40% of the specified allowance.
Remaining tolerance is the numerical difference between the specified roundness limit and the calculated roundness error.
A positive value indicates that the calculated error remains within the entered limit. Zero means the result is exactly at the limit, while a negative value indicates that the limit has been exceeded.
This calculator provides a simplified numerical roundness calculation from maximum and minimum measured values. It does not perform a complete least-squares, minimum-zone or minimum-circumscribed-circle evaluation.
Actual circularity inspection can depend on the specified measurement method, number and distribution of measurement points, filtering, instrument capability and applicable engineering standard.
What is roundness error? It is the measured deviation of a circular feature from an ideal circular form.
How is roundness error calculated from diameters? Maximum measured diameter minus minimum measured diameter gives the simplified diametral variation.
How is roundness error calculated from radii? Maximum measured radius minus minimum measured radius gives the simplified radial variation.
Can this tool be used for shafts? Yes. It can be used for preliminary numerical checks of shafts, journals and other circular features.
Is roundness the same as runout? No. Roundness is a form characteristic, while runout is evaluated relative to a datum axis during rotation.
What does 100% tolerance utilization mean? The calculated roundness error is exactly equal to the specified limit.
Does PASS certify the part? No. PASS only means the simplified calculated value is within the entered numerical limit.