Metric & Imperial Measurement
Accurate measurement is the foundation of designing and
manufacturing products. A good understanding of the basics of
measuring is essential in this course and is an extremely valuable
skill in the work world and life in general.
The two systems used in industry are the Metric system and the
Imperial (Inch) system. Although here in Canada the educational
system has adopted the Metric system of measure it is essential to be
able to utilize both systems and convert between the two.
Metric rulers are fairly easy to read. They deal with centimeters and millimeters
only. You won’t have to worry much about fractions.
Take a look at the following Metric Ruler.
The larger lines with numbers are centimeters, and the smallest lines are
millimeters. Since millimeters are 1/10th of a centimeter, if you measure 7 marks
after a centimeter, it is 1.7 centimeters long.
One of the most advantageous benefits of the metric system
is the ease at which one can convert between units. Metric
measurement is based on powers of 10 which are
designated with a prefix.
These prefixes are used with the base unit of the various
Ex. 2.5 cm = 25 mm, 500 mL= 0.5 L
1.6 Km = 1600 m
English (Imperial) rulers, are more difficult to read, mainly because they deal with
fractions, which are a bit more difficult to learn.
Take a look at the following English Rulers marked out in inches.
A ruler marked in 8ths. Every mark is 1/8th of an inch.
A ruler marked in 16ths. Every mark is 1/16th of an inch.
Understanding The Inch
To understand an imperial ruler we just have to understand how 1" is broken
down. The image below represents a 1” division on a ruler.
If we split that1 inch division into 2 equal parts, the mark represents the ½ inch
If we once again split these sections in half again, we now have 4 equal sections
a ¼ of an inch each.
The division of these sections continues further to create 1/8 division.
This patern may continue to 1/32 and then 1/64 divisions depending on the
accuracy of the ruler or tape measure. After 1/64 it would be too hard to see the
divisions on the ruler and therefore would add no additional accuracy.
Expressing Fractional Measurements In Decimal Form
Imperial units can also be expressed in decimal form. Converting to decimal
equivalents is usually performed because a greater degree of accuracy is
In manufacturing we often work to tolerances within a thousands of and inch
(1/1000 or 0.001"). If you divide 1 inch into 1000 equal sections, one of those
sections is a thousandth of and inch. The average human hair is roughly three
one thousandths of an inch in diameter (i.e. 3/1000 or 0.003").
So if we look at divisions on a ruler that is broken down into 1/16, we can see
how fractional measurements can be converted into decimal equivalents. (They
are the same but show a greater degree of accuracy).
Converting units in the imperial system is not as easy. For this we require a
conversion table, some basic math skills and preferably a calculator.
The table below outlines some various conversions in the imperial system.
Length 12 inches (in.) = 1 foot (ft.)
3 foot (ft.) = 1 yard (yd.)
1760 yards (yd.) = 1 Mile (ml.)
Converting Metric ↔ Imperial
One of the common skills employers say teens have trouble with when they enter
the work force is the ability to measure in Imperial units and convert between
Imperial and Metric units.
To do this we require some basic conversion relationships and preferably a
For length measurements: 1 inch = 2.54 cm or 1 inch = 25.4 mm
Ex. Convert 12.7 cm to inches?
1 inch = 2.54 cm therefore 12.7 cm / 2.54 cm = 5 inches
Ex. Convert 5 ¾ inches to mm?
1 inch = 25.4 mm therefore 5 ¾ inches x 25.4 mm = 146.05 mm