Screw Gauge to MM Converter
Pick a screw gauge (#6, #8, #10…) and get the diameter in inches and millimeters — or enter millimeters to find the nearest gauge. No more guessing what #8 means.
How It Works
US screw gauge runs on a formula, not a table: diameter in inches = 0.060 + 0.013 × gauge number. So #6 is 0.138 in (3.51 mm) and #10 is 0.190 in (4.83 mm). Above #12 the trade switches to fractional sizes (1/4 in and up), which is why the gauge numbers skip. Metric screws skip gauge entirely — M4 means 4 mm — which is why the converter also runs in reverse.
Printable PDF
Download the Screw Gauge to MM Converter and its formula sheet as a free PDF.
Free download. (Email capture can be wired to a form provider later — see README.)
Reference values only — always confirm critical fastening decisions against your engineering specification or the fastener manufacturer.