Sockets
Metric to SAE conversion across all 47 common sizes, with interchangeability ratings, plus impact, deep well and drive size references.
About SocketConversion.com
SocketConversion.com is a free size reference for mechanics, technicians and engineers who work across metric and SAE fasteners. It exists because the two systems never line up: one inch is defined as exactly 25.4mm, and since neither standard chose its increments with the other in mind, almost every conversion lands between two available tool sizes rather than on one.
That gap is where fasteners get rounded. Knowing that 19mm and 3/4" differ by two thousandths of an inch, while 10mm and 3/8" differ by nineteen, is the difference between a socket that holds and one that shears the corners off a bolt head. Every chart on this site reports that difference explicitly rather than presenting conversions as clean equivalences, and rates whether a substitution is actually safe to make.
What This Site Covers
Wrenches
Metric to SAE wrench sizing under a tighter tolerance than sockets, covering open-end, box-end and Whitworth spanner conventions.
Bolts & threads
Bolt head dimensions matched to thread specs, grade markings, and metric, UNC, UNF and Whitworth thread standards compared side by side.
Drills & taps
Number, letter, fractional and metric drill sizes with decimal equivalents, and tap drill sizes for every common thread.
How the Data Is Produced
Conversion values are calculated from the exact definition of one inch as 25.4mm rather than transcribed from other charts, so the decimal and millimetre columns are correct by construction. Size designations, thread pitches, tap drills and grade markings follow standard engineering references: ISO and DIN for metric fasteners, ANSI and Unified series for inch fasteners, and British Standard Whitworth for pre-metric British hardware. Where two standards specify different values for the same fastener, as ISO and DIN do for several metric bolt heads, both are shown rather than one being silently picked.
SocketConversion.com has no affiliation with any tool manufacturer, sells nothing, and does not recommend brands beyond describing how different tool geometries behave. Where a page mentions a manufacturer it is to explain a design difference, not to endorse a product.
Where to Start
The metric to standard socket conversion calculator is the main tool and converts in both directions with an interchangeability rating for every pairing. If you are working from an inch size toward a metric one, the SAE to metric converter runs the same data in reverse. For wrenches rather than sockets, the wrench size chart applies a tighter tolerance band, because an open-end jaw grips two flats where a socket grips six. Every chart on the site is listed in one place on the HTML sitemap, and corrections and suggestions are welcome via the contact page.
All Conversion References
Every size chart and calculator on the site.
Bolt Size Chart Bolt head dimensions matched to the socket that fits them Drill Size Chart Number, letter, fractional and metric drill bit sizes Tap Drill Chart Correct drill size before cutting metric or SAE threads Thread Size Chart Metric, UNC, UNF and Whitworth thread standards compared Impact Socket Sizes Impact-rated socket sizing for 1/4 through 3/4 inch drives Deep Socket Sizes Deep well socket lengths for recessed fasteners Drive Size Adapters Stepping between 1/4, 3/8, 1/2 and 3/4 inch drive sizes mm to Inches General millimetre to fractional inch conversion Fraction to Decimal Wrench fraction to decimal inch reference Allen Wrench Sizes Metric and SAE hex key equivalents