UnitCharts

Last updated: 14 October 2026

About UnitCharts

UnitCharts is a small collection of reference tables for the measurements people actually have to look up: wire gauges, abrasive grit, drill and tap sizes, bolt and fastener dimensions, hardness scales, pipe and flange sizes, and textile sizes.

Why this site exists

Most of these tables are already published somewhere — usually as a PDF, a scanned catalogue page, or an image that cannot be searched or scaled on a phone. The numbers are fine; the delivery is not. This site takes the same published standards and presents them as plain, fast, searchable tables that work on any screen.

What is here

There are 30 tables, grouped into six categories:

  • Electrical — AWG wire gauge, cable ampacity (NEC), fuse and breaker ratings, battery sizes.
  • Machining — drill bit sizes, tap drill and thread sizes, metric thread stress areas, pipe schedules, AN fittings, bearing bores, hardness conversion and surface roughness.
  • Hardware — metric bolt head sizes, wrench sizes, bolt grades, washers, flanges, O-rings, sheet metal and steel sheet gauges, wood screws, sockets and nails.
  • Abrasives — sandpaper grit conversion between FEPA P-grades, CAMI numbers and micron sizes.
  • Textile — knitting needle, crochet hook and yarn weight conversions.
  • Music — guitar string gauges by set and string.

Where the numbers come from

Values are taken from published, public standards and converted where necessary. The main sources are:

  • AWG wire diameters — the exact AWG definition (d = 0.005 × 92^((36−n)/39) inches), which reproduces the tabulated ASTM B258 values.
  • Ampacity — NFPA 70 (NEC) Table 310.16, copper and aluminium, 60 / 75 / 90 °C columns.
  • Fasteners — ISO 4014 / 4017 hex bolts, ISO 4762 socket head screws, ISO 7089 washers, ISO 898-1 and SAE J429 strength grades, ISO 724 thread stress areas.
  • Hardness — ASTM E140 and ISO 18265 conversion tables for carbon and low-alloy steels.
  • Surface finish — ISO 1302 N-grades and ISO 21920 Ra / Rz values.
  • Flanges — ASME B16.5 Class 150 and 300.
  • O-rings — SAE AS568 series, tolerances per ISO 3601-1A.
  • Pipe — ASME B36.10 for nominal pipe size, outside diameter and wall thickness.
  • Abrasive grit — FEPA P-grades (FEPA 43-GB / ISO 6344) and CAMI/ANSI average particle sizes.
  • Drill and tap sizes — ANSI B94.11M decimal equivalents and standard tap drill recommendations.
  • Sheet and plate — the US Standard Gauge fixed by 15 U.S. Code § 206.
  • Batteries — IEC 60086 and ANSI C18 dimensions and designations.
  • Spring wire — ASTM A228 music wire diameters and tensile ranges.
  • Textile sizes — CYC yarn weight categories, and standard US/UK/metric needle and hook conversions.
  • Bearings and fittings — the relevant ISO, ANSI and commercial standard conversions.

How to use it

Every table has a search box. Type part of a value — a fraction, a millimetre figure, a gauge number, a grade — and the table filters as you type. Some tables also carry a filter for the series or system (for example number, letter and fractional drill bits, or the metric and imperial wrench sizes).

Where a table lists more than one published convention — sandpaper grit is the usual example, as are the old DIN versus ISO metric bolt heads — the notes below the table say which convention the numbers follow.

Reference use only. These tables are provided for general reference. They are not engineering, electrical, medical or safety advice, and they are not a substitute for the standard itself or for the judgement of a qualified person. Dimensions and ratings are standardised, but the correct choice always depends on the specific application, material and the code that applies where you are working. Several standards referenced here exist in published editions that have been revised over time — where a value matters, verify it against the current edition of the controlling standard before you cut, drill, wire, tap or specify anything.

Corrections

If you spot a number that is wrong, please tell us — a source or standard reference helps us fix it quickly. Accuracy is the whole point of a reference table, so corrections are welcome and taken seriously.