| 1. | Definition of the System SI |
| 1.1 | The SI units belong to the International System of Units, of which the international abbreviation of the name is «SI» |
| 1.2 | The SI units consist of: |
| the base units; |
| the derived units; |
| 2. | Base units: |
| 2.1 | The names and symbols of the base units are respectively |
| for length | metre | m |
| for mass | kilogram | kg |
| for time | second | s |
| for electric current | ampere | A |
| for thermodynamic temperature | kelvin | K |
| for amount of substance | mole | mol |
| for luminous intensity | candela | cd |
| 2.2 | Definitions of base units: |
| The base units shall have the definitions assigned by the Minister from time to time by way of regulations, being the meaning appearing to the Minister to reproduce in English the international definition adopted by the General Conference of Weights and Measures(CGPM) and in force at the date of the making of the regulations. |
| 3. | Derived units: |
| 3.1 | The derived units are formed by combining base units with each other, by combining base units with other derived units, and by combining derived units with each other, according to the algebraic relations linking the corresponding quantities. The symbols for derived units are obtained by means of the mathematical signs for multiplication, division and use of exponents. Most commonly used derived units are indicated in sections 3.2, 3.3, 3.4, 3.5, 3.6 and 3.7. |
| 3.2 | Units of Space, Time and Periodic Phenomena |
| 3.2.1 | Plane angle: radian (symbol: rad). |
| The radian is the plane angle between 2 radii
which cut off on the circumference of a circle an arc equal in length to the radius. |
| |
| 3.2.2 | Solid angle: steradian (symbol: sr). |
| The steradian is the solid angle, which having its vertex in the centre of sphere, cuts off an area of the surface of the sphere equal to that of a square with its side of equal length to the radius of the sphere. |
| |
| 3.2.3 | Wave number: 1 per metre (symbol: m-1). |
| 1 per metre is the wave number of a monochromatic radiation whose wave length is equal to 1 metre. |
| |
| 3.2.4 | Area: the square metre (symbol: m2). |
| The square meter is the surface of a square having a side of 1 metre. (1 m-2 =1m•m.). |
| 3.2.5 | Volume: the cubic metre (symbol: m3). |
| The cubic metre is the volume of a cube having a side of 1 metre. (1 m3 = 1 m•m•m). |
| 3.2.6 | Frequency: the hertz (symbol: Hz). |
| The hertz is the frequency of a periodic phenomenon of which the periodic time is 1 second. |
| |
| 3.2.7 | Angular velocity: radian per second (symbol: rad/s or rad•s-1). |
| The radian per second is the angular velocity of a body which, animated by a uniform rotation around a fixed axis, turns 1 radian in 1 second. |
| |
| 3.2.8 | Angular acceleration: radian per second squared (symbol: rad/s2 or rad•s-2). |
| The radian per second squared is the angular acceleration of a body which is animated by a rotation varying uniformly around a fixed axis, and whose angular velocity varies by 1 radian per second in 1 second. |
| |
| 3.2.9 | Speed: metre per second (symbol: m/s or m•s-1). |
| The metre per second is the speed of a body which, animated by a uniform movement, covers 1 metre in 1 second. |
| |
| 3.2.10 | Acceleration: metre per second squared (symbol: m/s2 or m•s2). |
| The metre per second squared is the acceleration of a body, animated by a uniformly varied movement whose speed varies in 1 second by 1 metre per second. |
| |
| 3.3 | Units of Mechanics |
| 3.3.1 | Linear density: kilogram per metre (symbol: kg/m or kg•m-1). |
| The kilogram per metre is the linear density of a homogeneous body of uniform section having a mass of 1 kilogram and a length of 1 metre. |
| |
| 3.3.2 | Surface density: kilogram per square metre (symbol: kg/m2 or kg•m-2). |
| The kilogram per square metre is the density of a homogeneous body having a mass of 1 kilogram and a surface area of one square metre. |
| |
| 3.3.3 | Density (mass density): kilogram per cubic metre (symbol: kg/m3 or kg•m-3). |
| The kilogram per cubic metre is the density of a homogeneous body having a mass of 1 kilogram and a volume of 1 cubic metre. |
| |
| 3.3.4 | Force: newton (symbol: N). |
| The newton is the force which, when applied to a body having a mass of 1 kilogram, gives it an acceleration of 1 metre per second squared. |
| (1N = 1 kg•m/s2). |
| 3.3.5 | Pressure, Stress: pascal (symbol: Pa). |
| The pascal is the uniform pressure which, when acting on a plane surface of 1 square metre, exercises perpendicularly to that surface a total force of 1 newton. It is also the uniform stress which, when acting on a plane surface of 1 square meter, exercises on that surface a total force of 1 newton. |
| |
| 3.3.6 | Dynamic viscosity: pascal second (symbol: Pa•s). |
| The pascal second is the dynamic viscosity of a homogeneous fluid in which the uniform linear movement of a plane surface of 1 square metre leads to a retarding force of 1 newton, when there is a difference in velocity of 1 metre per second between 2 parallel planes separated by a distance of 1 metre. |
| |
| 3.3.7 | Kinematic viscosity: metre squared per second (symbol: m2/s or m2•s-1). |
| The metre squared per second is the kinematic viscosity of a fluid whose dynamic viscosity is 1 pascal second and whose density is 1 kilogram per cubic metre. |
| |
| 3.3.8 | Work, Energy, Quantity of heat: joule (symbol: J). |
| The joule is the work done when the point of application of a force of 1 newton is displaced through a distance of 1 metre in the direction of the force. |
| (1J = 1 N•m) |
| 3.3.9 | Power, Energy flow rate, Heat flow rate: watt (symbol: W). |
| The watt is the power which gives rise to a production of energy equal to 1 joule per second. |
| |
| 3.3.10 | Volume flow rate: cubic metre per second (symbol: m3/s or m3•s-1). |
| The cubic metre per second is the volume flow rate of a uniform flow such that a substance having a volume of 1 cubic metre passes through the cross section considered in 1 second. |
| |
| 3.3.11 | Mass flow rate: kilogram per second (symbol: kg/s or kg•s-1). |
| The kilogram per second is the mass flow rate of a uniform flow such that a substance having a mass of 1 kilogram passes through the cross section considered in 1 second. |
| |
| 3.4 | Units of Heat |
| 3.4.1 | Entropy: joule per kelvin (symbol: J/K or J•K-1). |
| The joule per kelvin is the increase in the entropy of a system receiving a quantity of heat of 1 joule at the constant thermodynamic temperature of 1 kelvin, provided that no irreversible change takes place in the system. |
| |
| 3.4.2 | Specific heat capacity: joule per kilogram kelvin (symbol: J/(kg•K) or J•kg-1•K-1) |
| The joule per kilogram kelvin is the specific heat capacity of a homogeneous body having a mass of 1 kilogram in which the addition of a quantity of heat of 1 joule produces a rise in temperature of 1 kelvin. |
| |
| 3.4.3 | Thermal conductivity: watt per metre kelvin symbol: W/(m•K) or W•m-1•K-1). |
| The watt per metre kelvin is the thermal conductivity of a homogeneous body in which a difference of temperature of 1 kelvin between 2 parallel planes having a surface of 1 square metre and which are 1 metre apart produces between these planes a heat flow rate of 1 watt. |
| |
| 3.5 | Units of Electricity and Magnetism |
| 3.5.1 | Quantity of electricity, Electric charge: coulomb (symbol: C). |
| The coulomb is the quantity of electricity carried in 1 second by a current of 1 ampere. |
| (1 C = 1 A•1 s = 1 A•s). |
| 3.5.2 | Electric potential, Electric tension, Electromotive force: volt (symbol: V). |
| The volt is the difference of electric potential between 2 points of a conducting wire carrying a constant current of 1 ampere, when the power dissipated between these 2 points is equal to 1 watt. |
| |
| 3.5.3 | Electric field strength: volt per metre (symbol: V/m). |
| The volt per metre is the strength of the electric field which exercises a force of 1 newton on a body charged with a quantity of electricity of 1 coulomb. |
| |
| 3.5.4 | Electric resistance: ohm (symbol: Ω) |
| The ohm is the electric resistance between 2 points of a conductor when a constant potential difference of 1 volt, applied to these points, produces in the conductor a current of 1 ampere, the conductor not being the seat of any electromotive force. |
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| 3.5.5 | Conductance: siemens (symbol: S). |
| The siemens is the conductance of a conductor having an electric resistance of 1 ohm. |
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| 3.5.6 | Electric capacitance: farad (symbol: F). |
| The farad is the capacitance of a capacitor between the plates of which there appears a difference of electric potential of 1 volt, when it is charged by a quantity of electricity of 1 coulomb. |
| |
| 3.5.7 | Inductance: henry (symbol: H). |
| The henry is the electric inductance of a closed circuit in which an electromotive force of 1 volt is produced when the electric current in the circuit varies uniformly at the rate of 1 ampere per second. |
| |
| 3.5.8 | Magnetic flux, magnetic induction flux: Weber (symbol: Wb). |
| The weber is the magnetic flux which, linking a circuit of 1 turn, would produce in it an electromotive force of 1 volt, if it were reduced to zero at a uniformed rate in 1 second. |
| (1 Wb = 1V•s). |
| 3.5.9 | Magnetic induction, magnetic flux density: tesla (symbol: T). |
| The tesla is the uniform magnetic induction, which, distributed normally over a surface of 1 square metre, produces across the surface a total magnetic flux of 1 weber. |
| |
| 3.5.10 | Magnetomotive force: ampere (symbol: A). |
| The ampere is the magnetomotive force along any closed curve which surrounds once only an electric conductor through which an electric current of 1 ampere passes. |
| 3.5.11 | Magnetic field strength: amper per metre (symbol: A/m or A•m-1). |
| The ampere per metre is the strength of the magnetic field produced in vacuum along the circumference of a circle of 1 metre circumference, by an electric current of 1 ampere, maintained in a straight conductor of infinite length, of negligible circular cross section, forming the axis of the circle mentioned. |
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| 3.6 | Units of Light and Electromagnetic Radiation |
| 3.6.1 | Radiant intensity: watt per steradian (symbol: W/sr or W•sr-1). |
| The watt per steradian is the radiant intensity of a point source emitting a uniform radiant flux of 1 watt in a solid angle of 1 steradian. |
| |
| 3.6.2 | Luminance: candela per square metre (symbol: cd/m2 or cd•m-2). |
| The candela per square metre is the luminous luminance perpendicular to the plane surface of 1 square metre of a source of which the luminous intensity perpendicular to that surface is 1 candela. |
| |
| 3.6.3 | Luminous flux: lumen (symbol: 1m). |
| The lumen is the luminous flux emitted in the unit solid angle (steradian) by a uniform point source having a luminous intensity of 1 candela.v |
| (1 lm = 1 cd•sr) |
| 3.6.4 | Illuminance: lux (symbol: 1x). |
| The lux is the illuminance of a surface receiving a luminous flux of 1 lumen, uniformly distributed over a square metre of the surface. |
| |
| 3.7 | Units of Ionizing Radiations |
| 3.7.1 | Activity (of a radioactive source): becquerel (Symbol: Bq). |
| The becquerel is the activity of a radioactive source in which one nuclear transformation or transition occurs per second. |
| |
| 3.7.2 | Absorbed dose: gray (symbol: Gy). |
| The gray is the dose absorbed in an element of matter of 1 kilogram mass to which the energy of 1 joule is imparted by ionizing radiations whose energy fluence is constant. |
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| 3.7.3 | Exposure: coulomb per kilogram (symbol: C/kg or C•kg-1). |
| The coulomb per kilogram is the exposure of a photonic ionizing radiation which can produce in a quantity of air of 1 kilogram mass, ions of one sign carrying a total electric charge of 1 coulomb, the energy fluence being uniform in the quantity of air considered. |
| 4. | Decimal Multiples and Sub-multiples of SI Units |
| 4.1 | The decimal multiples and sub-multiples of SI units are formed by means of the decimal numerical factors set out in subsection 4.2 by which the SI unit concerned is multiplied. |
| 4.2 | The names of the decimal multiples and sub-multiples of the SI units are formed by means of SI prefixes designating the decimal numerical factors. |