Rule - Measuring tool

The most common, and the best known, piece of measuring equipment is the ordinary rule.

The rule or tape is used for measuring where accuracy is not an extremely critical factor. They can be rigid or flexible, come in various lengths, and can be made of wood, metal, cloth, fiberglass...

A rule, is an instrument used in geometry, technical drawing and engineering/building to measure distances and/or to rule straight lines.

 Plastic rule

Warning: Measure twice, cut once.

Considerable frustration and additional expense can be avoided by checking for a second time that the required measurement is accurately marked.

Rules may be flexible or nonflexible, but the thinner the rule, the easier it is to measure accurately because the division marks are closer to the work.

Store rules carefully. If the edges and  ends are damaged, there will be inaccuracies. Many rules have a hole in one end so they can be hung up out of harm’s way

A 150mm (6 inch)  and a 300mm (12 inch) rule with both metric and imperial markings will cover most needs.

The rule can also be used as a straight edge.


Put the rule flat on object and read the measurement from the rule.

Measuring with rule

Keep the rule at a right angle to the object.

 Measuring with rule at a right angle

Read the measurement from directly above the rule.

Accurate measuring with rule      inaccurate measuring with rule    

In making several small measurements do not move the rule.


If the ruler is thicker

To measure and mark distances for accurate work, lay the rule on edge so that the divisions on its side touch the stock.

Marking with pencil during measuring

If the end of the rule is inaccurate, start measuring at the 1cm mark.

Measuring outside diameter of a pipe

 Measuring outside diameter of a pipe

Measuring inside diameter of a pipe

Measuring inside diameter of a pipe

Measuring the length of a bolt or screw

Measuring the length of a bolt or screw
Whenever there are several measurements to be made along a straight line, the rule should not be raised until all are made, for with each placing of the rule errors are likely to occur.

The rule is used to find the middle of an edge by placing it across the piece so that the distances from the edges of the piece to corresponding fractional marks, shall be the same. The middle of the piece being at a point midway between the marks selected.

 Finding middle of a piece - Method 1

Next image illustrates a second method of finding middle of a piece. Lay the rule across the piece at an angle such that two of the unit marks shall rest each upon an arris. The middle of the piece will then be at that unit mark which is midway between these.

 Finding middle of a piece - Method 2
If it is desired to divide a piece into more than two parts lay the rule across the piece at such an  angle as will bring two of its unit marks each upon an arris  with the required number of divisions between. Next image shows a piece divided into three equal parts.

 Piece divided into three equal parts

Wooden ruler (Bench rulers)

Wooden rule is the woodworker’s traditional measuring instrument. The rule itself is made from hardwood and is marked out in metric (millimetres) or imperial (inches); some rules have both.

Wooden rule

The wooden rule doaes have some disadvantages:
- It can be broken quite easily
- Its edges can be damaged through regular use affecting the accuracy of your measurement

Steel rule (Engineer’s steel rules)

Engineer's steel rule


A steel rule is essential for any kind of metal work and is also a useful tool in the woodwork workshop. The steel rule is much more versatile and durable than wooden rule.  Steel rules should be oiled to prevent rusting when not in use. Steel rules may be flexible or non flexible, but the thinner the rule, the easier it is to measure accurately because the division marks are closer to the work.

Folding rule (Zig – zag rule, jointed rule, surveyor’s rod)

The folding rule can be used in a confined space where a long rule would be inconvenient. It also overcomes the problem of carrying a long measuring rod to the workplace. It is the rule most often used by carpenters. Folding rule is made from hardwood and reinforces at the ends with brass. The rule is usually made from strips, hinged in pairs to fold back on one another.

Folding rule

The folding rules cannot be relied on for extremely accurate measurements because a certain amount of play develops at the joints after continued use.

Extension rule

The extension rule is a folding rule which includes a brass slide for making internal measurements. The slide can also be used as a depth gauge. The slide extends from the first strip of the rule

Steel tape (tape measure, push – pull steel tape, flexible rule, retractable steel tape measure, flex tapes)

Push pull steel tape
The steel tape measure is an extendable steel strip coiled into a container. The tape is spring loaded. So that as soon as it is released it will automatically return to the case.

Steel tapes are made from 2m to about 10m in length. The shorter tapes are made with a curved, but rigid, cross section flexible enough to be rolled up. Long, flat tapes need support over their full length to avoid sagging. Lack of support can cause reading errors.

There are many tapes made to suit special needs. The steel tape is made of flexible spring steel. Pocket steel tapes (push – pull steel tape) are shorter types of steel tapes. The flexible rigid push pull steel tapes are usually contained in metal or plastic cases into which they wind themselves when a button is presses, or into which they can be easily pressed. A hook is provided at one end to hook over the object being measured so one man can handle it. The graduations are printed on only one face of the tape.

A good tape will retract automatically and smoothly.

Wind up tape measuring

The wind up tape measure is primarily designed for measuring large dimensions, such as the size of a room.

 Wind up tape measure

Soft rule (soft tape measure)

A tape measure or measuring tape is a flexible form of rule. It consists of a ribbon of cloth, plastic, or fiber glass  strip with linear-measurement markings.

Tape measures that were intended for use in tailoring  or dressmaking were made from flexible cloth or plastic.
Tape measure

1. Keep rules and tapes clean and dry.
2. Store rules and tapes where they will not become bent or damaged.