A hook gauge or needle gauge is a measuring device used by crochet

Crochet

Crochet is a process of creating fabric from yarn, thread, or other material strands using a crochet hook. The word is derived from the French word "crochet", meaning hook. Hooks can be made of materials such as metals, woods or plastic and are commercially manufactured as well as produced by...

ers and knitters to test the sizes of particular crochet hook

Crochet hook

A crochet hook is a type of needle with a hook at one end used to draw thread through knotted loops. Only one crochet hook is needed to make crochet stitches. The crochet hook's earliest use appears to have been in the late 18th century or early 19th century.Typical materials for crochet hooks...

s and knitting needle

Knitting needle

A knitting needle or knitting pin is a tool in hand-knitting to produce knitted fabrics. They generally have a long shaft and taper at their end, but they are not nearly as sharp as sewing needles. Their purpose is two-fold...

s. Hook gauges are usually made of plastic or aluminum and have sizing holes from 2mm to 11mm diameter. A hook gauge also functions as a ruler to test the size of a test swatch of handmade fabric

Fabric

A fabric is a textile material, short for "textile fabric".Fabric may also refer to:*Fabric , the spatial and geometric configuration of elements within a rock*Fabric , a nightclub in London, England...

.Stoller, p. 23.

Sizing conventions

A hook gauge is the most reliable way to determine the actual size of a tool. Even though most hooks and needles have metric

Metric system

The metric system is an international decimalised system of measurement. France was first to adopt a metric system, in 1799, and a metric system is now the official system of measurement, used in almost every country in the world...

 sizing, tool dimensions vary slightly between different manufacturers. Non-metric sizing conventions also change over time. For instance, different sizing charts rate a 4.0mm hook as either a U.S.

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 G/6 or an F/5.

Importance of accurate sizing

U.S. textile craft

Textile arts

Textile arts are those arts and crafts that use plant, animal, or synthetic fibers to construct practical or decorative objects.Textiles have been a fundamental part of human life since the beginning of civilization, and the methods and materials used to make them have expanded enormously, while...

 terminology employs the word gauge in two different ways: as hook gauge in reference to the sizing tool, or as a standalone term gauge

Gauge (knitting)

In knitting, the word gauge is used both in hand knitting and machine knitting; the latter, technical abbreviation GG, refers to "Knitting Machines" fineness size. In both cases, the term refers to the number of stitches per inch, not the size of the finished garment...

 to describe the number of stitch

Stitch (textile arts)

In the textile arts, a stitch is a single turn or loop of thread or yarn. Stitches are the fundamental elements of sewing, knitting, embroidery, crochet, and needle lace-making, whether by hand or machine...

es in a standard sized sample of work, usually 4" or 10cm. UK terminology refers to the latter as tension. Craft patterns include a gauge or tension measurement and good practice among crafters is to achieve the correct gauge on a sample swatch before embarking on the full project.

As one crochet guidebook explains:

Whenever you are following a crochet pattern you will notice that a gauge is included. This is an all-important guide to obtaining the proper size of the square or garment you are working on. If you don't get the proper gauge, the item will not fit properly and you may run out of yarn

Yarn

Yarn is a long continuous length of interlocked fibres, suitable for use in the production of textiles, sewing, crocheting, knitting, weaving, embroidery and ropemaking. Thread is a type of yarn intended for sewing by hand or machine. Modern manufactured sewing threads may be finished with wax or...

before finishing.

Several factors affect fabric gauge including hook or needle size, although sometimes a crafter may change tool size deliberately in order to achieve a certain gauge. Accurate needle and hook sizing reduces the number of variables that affect these decisions. Additionally, if substitute tools are needed during the course of the project a hook gauge can determine whether a given tool is appropriate in advance of actual work.