Dual-Dimension Tolerance Rounding Tool

Use this Dual-Dimension Tolerance Calculator to convert dimensions and tolerances between mm and inches. It utilizes the “inward rounding” methodology to prevent tolerance growth or inversion, ensuring your converted limits and bilateral deviations maintain the original design intent. An aid for engineering and professional drawing unit conversion.

Aged mechanical drawing with curled corner

This Dual-Dimension Tolerance Rounding Tool is designed to be an aid for professionals who convert engineering dimensions and tolerances between metric (mm) and imperial (in) units.

Therefore, its core purpose is to address the critical risk of tolerance inversion or tolerance growth that can occur when mathematically rounding converted limits. The utility applies a methodology commonly referred to as “inward rounding,” which helps ensure the calculated secondary tolerance zone remains contained within the original primary zone. Although SOLIDWORKS has similar functionality built-in, there may be other times when this calculation is necessary but not available in a particular software.

By presenting limits or bilateral deviations derived from this methodology, the tool assists in reducing manual calculation errors and provides a valuable general reference for maintaining the part’s original design intent.

Note on Use: This utility uses the online decimal.js library for precision; so whether you download the utility or use it here, you’ll need internet access. As always, the results generated should be verified by a professional and used in accordance with your organization’s standards.

Dual-Dimension Tolerance Rounding Tool

Rounded Secondary Dimension (in)
Tolerance Range Comparison (Upper Limit is Left, Lower Limit is Right)
UPPER LIMIT (+Dev) LOWER LIMIT (-Dev)
If Sec. Nom. falls outside the Secondary Range, the condition may be invalid.

The utility is based on online sources, particular assumptions and calculations. This utility should only be used as a general reference. Results should always be verified. No one is responsible for incorrect information generated by this utility. Use thereof is the sole responsibility of the user. Use at your own risk.

DualDimensionTolRoundingTool.zip

Author: fcsuper

As a drafter, mechanical designer and CAD engineer, I've been in the mechanical design field since 1991. For the first 8 years of my career, I was an AutoCAD professional. I utilized AutoLISP and many other AutoCAD customization features to streamline drafting activities for 6+ drafters and designers. I authored several custom functions, one of which was published in the March 1997 issue of Cadalyst Magazine. Since 1998, I've been used SolidWorks non-stop. I've worked to utilize the SolidWorks' user environment to simplify drafting and design activities for 20+ engineers. I've created this website to provide current information about SolidWorks from a variety of contributors. More recently, I am now employed by Dassault Systemes as SOLIDWORKS Sr. Product Definition Manager to improve drawing, annotation and MBD related areas.

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