Metric and Standard Measurements (Symbols and Guidelines)

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Metric and Standard Measurements (Symbols and Guidelines)

1 Introduction

In 1970, Parliament unanimously endorsed the White Paper on Metric Conversion in Canada proposing the adoption of the most up-to-date metric system of measurement, the International System of Units or SI. Metric Commission Canada was established by order in council in June 1971 to prepare an overall plan for metric conversion.

The joy of the metric system lies in its simplicity and universality. It is simple because all relationships between a unit and its multiples and sub-multiples in the system are in powers of 10. Universal, because most countries in the world -- well over 95% of the world's population -- use metric units and/or are converting to SI.

To achieve this universality, 17 nations signed the Treaty of the Metre in 1875 and set up an international body to standardize metric units throughout the world. Many countries have since signed the Treaty of the Metre, and international conferences on weights and measures (la Conference Generale des Poids et Mesures, or CGPM) are held at regular intervals. Canada made the metric system legal by the Weights and Measures Act of 1873, and signed the Treaty of the Metre in 1907.

In 1960, the CGPM adopted the International System of Units, with the international abbreviation SI, and this is the metric measurement system adopted by Canada in the Weights and Measures Act of 1971.

A more detailed treatment of SI and its use are referenced in two National Standards of Canada: The International System of Units (SI), CAN3-Z234.2-76, and the Canadian Metric Practice Guide, CAN3-Z234.1-79. Both of these documents have been approved by the Standards Council of Canada, and are available from the Canadian Standards Association, 178 Rexdale Boulevard, Rexdale, Ontario M9W 1R3.

2 SI Base Units

Quantity Name of Unit Symbol
length metre m
mass kilogram kg
time second s
electric current ampere A
thermodynamic temperature kelvin K
amount of substance mole mol
luminous intensity candela cd

SI is founded on seven base units: metre for length, kilogram for mass, second for time, ampere for electric current, kelvin for thermodynamic temperature, mole for amount of substance and candela for luminous intensity.

There are also two supplementary units:

Quantity Name of Unit Symbol
plane angle radian rad
solid angle steradian sr

3 Some Derived Units with Special Names

Name Equivalent
Quantity of Unit Symbol to
force newton N kg•m/sq.s
pressure pascal Pa N/ sq.m
work, energy, quantity of work joule J N•m
power, heat flow rate watt W J/s
quantity of electricity coulomb C A•s
electric potential volt V W/A
electric resistance ohm ω V/A
electric capacitance farad F C/V
magnetic flux weber Wb V•s
inductance henry H Wb/A
magnetic flux density tesla T Wb/ sq.m
frequency hertz Hz s-1
luminous flux lumen lm cd•sr
illuminance lux lx lm/ sq.m
absorbed dose of ionizing radiation gray Gy J/kg

Derived units are formed with base and / or supplementary units. In symbolic form they are expressed algebraically using the SI symbols with multiplication and / or division signs. For example, the derived unit for area is square metre (symbol sq.m); for density, kilogram per cubic metre (kg/sq.m); and for angular velocity, radian per second (rad/s). Some derived units have special names and symbols.

SI base units, supplementary units and derived units – but not their multiples and submultiples – form a “coherent” system of units.

4 Some Units Permitted for Use with SI

Quantity Name Symbol Value in SI Units
time minute min 1 min = 60 s
hour h 1 h = 3 600 s
day d 1 d = 86 400 s
year a
plane angle degree ° 1° = (π/180)rad
minute ' 1' = (π/10 800)rad
second " 1" = (π/648 000)rad
area hectare ha 1 ha = 1 h sq.m = 10 000 sq.m
volume litre L 1 L = 1
temperature degree Celsius* °C An interval of 1°C = 1 K
By definition 0°C = 273.15 K
mass tonne t 1 t = 1 000 kg = 1 Mg

These other units outside SI are also recognized for use with SI because of their practical importance.

    • The Celsius temperature scale, known as Centigrade prior to 1948, is named after the Swedish astronomer and physicist Anders Celsius (1701-1744), to avoid confusion with an angular measurement “centigrade”.

5 Common Symbols

Quantity Unit Symbol
length millimetre mm
length metre m
length kilometre km
mass gram g
mass kilogram kg
mass tonne t
force newton N
heat energy kilocalorie kcal
volume litre L
temperature degree Celsius °C

6 Common Prefixes

Prefix Means Multiply By Symbol
mega 1 000 000 M
kilo 1 000 k
hecta 100 h
deka 10 da
deci 0.1 d
centi 0.01 c
milli 0.001 m
micro 0.000 001 µ

7 Rules for Writing Symbols

.1 Symbols are always printed in upright type, irrespective of type face used in the rest of text: m g °C s
.2 Symbols are written in lower case except for unit names derived from proper names, as follows: m for metre; s for second; but N for newton; A for ampere.
NOTE: When the names of the units which derive from a proper name are written out in full, only Celsius takes a capital.
.3 Prefix symbols are in upright type without spacing between:
kg for kilogram, km for kilometre
.4 Symbols are never pluralized:
1 kg, 20 kg (not 20 kgs)
.5 Names and symbols should not be mixed:
kg or kilograms (not kgrams or kilog)
.6 Never use a period after a symbol unless it occurs at the end of a sentence.
.7 Always use a full space between numerals and symbols:
10 kg (not 10kg)
Exception: where first symbol is not a letter:
32°C (not 32° C or 32 °C)
.8 Symbols should be used in conjunction with numerals instead of unit names (when no numerals are involved, unit names should be used).
The roof area is 125 sq.m (not 125 square metres)
The roof area was given in square metres (not in sq.m)
The product of two or more units in symbolic form is indicated by a dot (or asterisk). Kg*m (not kg x m or kgm)

8 Rules for Writing Numerals

.1 Use decimals, not fractions:
0.25 kg (not 1/4 kg)
1.25 m (not 1-1/4 m)
2. Use a zero before a decimal point in numerals less than one.
0.45 kg (not .45 kg)
3. Use spaces not commas to separate long numerals into blocks of three:
3 000 000.25 (not 3,000,000.25)
Exception: This is optional on a four digit numeral.
1234.5 or 1 234.5 are both acceptable.
This rule is not applicable to the expression of amounts of money on negotiable instruments.

General Information