Screw Gauge Lookup Calculator
Enter a US screw gauge number (0–24) to find its major diameter.
Result
How to use
- Enter your values in the fields above.
- Press Calculate to see your result instantly.
- Use the Share button to copy a link to your result.
About this calculator
US screw sizes below 1/4 inch are labeled with a gauge number (like #4, #8, #10) rather than a fraction of an inch, a legacy numbering system that isn't self-evident from the number alone. The major (outer thread) diameter follows a simple linear formula: diameter = 0.060 + 0.013 × gauge inches.
This lookup is a practical reference for machinists, woodworkers, and DIYers who need to match a drill bit or nut to a screw's actual size, or convert an American gauge number into millimeters when working alongside metric hardware — a common point of confusion since the gauge number itself gives no direct sense of physical size.
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