SI units
SI units Systéme International d'Unités: the international system of units now recommended for all scientific purposes. A coherent and rationalized system of units derived from the m.k.s. units (a metric system based on the metre, kilogram, and second), SI units have now replaced c.g.s. units and Imperial units. The system has seven base units and two dimensionless units (formerly called supplementary units), all other units being derived from these nine units. There are 18 derived units with special names. Each unit has an agreed symbol (a capital letter or an initial capital letter if it is named after a scientist, otherwise the symbol consists of one or two lower-case letters). Decimal multiples of the units are indicated by a set of prefixes; when possible a prefix representing 10 raised to a power that is a multiple of three should be used.
TABLE 1.1 Base and dimensionless SI units
Physical quantity | Name | Symbol |
---|---|---|
*dimensionless units | ||
length | metre | m |
mass | kilogram | kg |
time | second | s |
ampere | A | |
thermodynamic temperature | kelvin | K |
luminous intensity | candela | cd |
amount of substance | mole | mol |
*plane angle | radian | rad |
*solid angle | steradian | sr |
TABLE 1.2 Derived SI units with special names
Physical quantity | Name of SI unit | Symbol of SI unit | |
---|---|---|---|
frequency | hertz | Hz | |
energy | joule | J | |
force | newton | N | |
power | watt | W | |
pressure | pascal | Pa | |
electric | charge | coulomb | C |
electric potential difference | volt | V | |
electric resistance | ohm | Ω | |
electric conductance | siemens | S | |
electric capacitance | farad | F | |
weber | Wb | ||
inductance | henry | H | |
magnetic flux density (magnetic induction) | tesla | T | |
luminous flux | lumen | lm | |
illuminance | lux | lx | |
absorbed dose | gray | Gy | |
activity | becquerel | Bq | |
dose equivalent | sievert | Sv |
TABLE 1.3 Decimal multiples and submultiples to be used with SI units
Submultiple | Prefix | Symbol | Multiple | Prefix | Symbol |
---|---|---|---|---|---|
10^{−1} | deci | d | 10 | deca | da |
10^{−2} | centi | c | 10^{2} | hecto | h |
10^{−3} | milli | m | 10^{3} | kilo | k |
10^{−6} | micro | μ | 10^{6} | mega | M |
10^{−9} | nano | n | 10^{9} | giga | G |
10^{−12} | pico | p | 10^{12} | tera | T |
10^{−15} | femto | f | 10^{15} | peta | P |
10^{−18} | atto | a | 10^{18} | exa | E |
10^{−21} | zepto | z | 10^{21} | zetta | Z |
10^{−24} | yocto | y | 10^{24} | yotta | Y |
TABLE 1.4 Conversion of units of SI units
From | To | Multiply by |
---|---|---|
in | m | 2.54 × 10^{−2} |
ft | m | 0.3048 |
sq. in | m^{2} | 6.4516 × 10^{−4} |
sq. ft | m^{2} | 9.2903 × 10^{−2} |
cu. in | m^{3} | 1.63871 × 10^{−5} |
cu. ft | m^{3} | 2.83168 × 10^{−2} |
l(itre) | m^{3} | 10^{−3} |
gal(lon) | l(itre) | 4.546 09 |
miles/hr | m s^{−1} | 0.477 04 |
km/hr | m s^{−1} | 0.277 78 |
lb | kg | 0.453 592 |
g cm^{−3} | kg m^{−3} | 10^{3} |
lb/in^{3} | kg m^{−3} | 2.767 99 × 10^{4} |
dyne | N | 10^{−5} |
poundal | N | 0.138 255 |
lbf | N | 4.448 22 |
mmHg | Pa | 133.322 |
atmosphere | Pa | 1.013 25 × 10^{5} |
hp | W | 745.7 |
erg | J | 10^{−7} |
eV | J | 1.602 10 × 10^{−19} |
kW h | J | 3.6 × 10^{6} |
cal | J | 4.1868 |
SI units
SI units (Système International d'Unités) pl. n. the internationally agreed system of units, based on the metre-kilogram-second system, now in use for all scientific purposes.
Table 11.1 Base and supplementary SI units
Physical quantity | Name of unit | Symbol for unit |
---|---|---|
length | metre | m |
mass | kilogram | kg |
time | second | s |
ampere | A | |
thermodynamic temperature | kelvin | K |
luminous intensity | candela | cd |
amount of substance | mole | mol |
*plane angle | radian | rad |
*solid angle | steradian | sr |
*supplementary units |
Table 11.2 Derived SI units with special names
Physical quantity | Name of unit | Symbol for unit |
---|---|---|
frequency | hertz | Hz |
energy | joule | J |
force | newton | N |
power | watt | W |
pressure | pascal | Pa |
electric charge | coulomb | C |
electric potential difference | volt | V |
electric resistance | ohm | Ω |
electric conductance | siemens | S |
electric capacitance | farad | F |
weber | Wb | |
inductance | henry | H |
magnetic flux density (magnetic induction) | tesla | T |
luminous flux | lumen | lm |
illuminance (illumination) | lux | lx |
absorbed dose | gray | Gy |
activity | becquerel | Bq |
dose equivalent | sievert | Sv |
Table 11.3 Decimal multiples and submultiples to be used with SI units
Submultiple | Prefix | Symbol | Multiple | Prefix | Symbol |
---|---|---|---|---|---|
10^{−1} | deci | d | 10^{1} | deca | da |
10^{−2} | centi | c | 10^{2} | hecto | h |
10^{−3} | milli | m | 10^{3} | kilo | k |
10^{−6} | micro | μ | 10^{6} | mega | M |
10^{−9} | nano | n | 10^{9} | giga | G |
10^{−12} | pico | p | 10^{12} | tera | T |
10^{−15} | femto | f | 10^{15} | peta | P |
10^{−16} | atto | a | 10^{16} | exa | E |
10^{−21} | zepto | z | 10^{21} | zetta | Z |
10^{−24} | yocto | y | 10^{24} | yotta | Y |
Table 11.4 Conversion of units to and from SI units
From | To | Multiply by |
---|---|---|
Temperature conversion | ||
°C (Celsius) = 5/9(°F − 32) | ||
°F (Fahrenheit) = (9/5 × °C) + 32 | ||
in | m | 0.0254 |
ft | m | 0.3048 |
sq in | m^{2} | 0.00064516 |
sq ft | m^{2} | 0.092903 |
cu in | m^{3} | 0.0000164 |
cu ft | m^{3} | 0.0283168 |
l(itre) | m^{3} | 0.001 |
gal(lon) | m^{3} | 0.0045609 |
gal(lon) | litres | 4.5609 |
lb | kg | 0.453592 |
g cm^{−3} | kg m^{−3} | 1000 |
lb/in^{3} | kg m^{−3} | 27679.9 |
mmHg | Pa | 133.322 |
cal | J | 4.1868 |
m | in | 39.3701 |
cm | in | 0.393701 |
cm^{2} | sq in | 0.155 |
m^{2} | sq in | 1550 |
m^{2} | sq ft | 10.7639 |
m^{3} | cu in | 61023.6 |
m^{3} | cu ft | 35.3146 |
m^{3} | l(itre) | 1000 |
m^{3} | gal(lon) | 219.969 |
kg | lb | 2.20462 |
kg m^{−3} | g cm^{−3} | 0.001 |
kg m^{−3} | lb/in^{3} | 0.0000363 |
Pa | mmHg | 0.0075006 |
J | cal | 0.238846 |
SI units
SI units (Système International d'Unités)
Quantity | Name of unit | Symbol | Equivalent | Reciprocal |
---|---|---|---|---|
length | metre | m | 3.281 feet | 1 ft = 0.3048 m |
mass | kilogram | kg | 2.2 pounds | 1 lb = 0.454 kg |
time | second | s | ||
ampere | A | |||
thermodynamic temperature | kelvin | K | 1°C = 1.8°F | 1°C = 1 K |
luminous intensity | candela | cd | ||
amount of substance | mole | mol |
Supplementary units
Quantity | Unit | Symbol |
---|---|---|
plane angle | radian | rad |
solid angle | steradian | sr |
Derived SI units
Quantity | Name of unit | Symbol | Equivalent | Reciprocal |
---|---|---|---|---|
frequency | hertz | Hz | ||
energy | joule | J | 0.2388 calories | 1 cal = 4.1868 J |
force | newton | N | 0.225 pounds force | 1 lbf = 4.448 N |
power | watt | W | 0.00134 horse power | 1 hp = 745.7 W |
pressure | pascal | Pa | 0.00689 pounds force/sq.inch | 1 lbf/sq.in = 145 Pa |
electric charge | coulomb | C | ||
electric potential difference | volt | V | ||
electric resistance | ohm | Ω | ||
electric conductance | siemens | S | ||
electric capacitance | farad | F | ||
weber | Wb | |||
inductance | henry | H | ||
magnetic flux density | tesla | T | ||
luminous flux | lumen | lm | ||
illuminance | lux | lx | ||
absorbed dose | gray | Gy | ||
activity | becquerel | Bq | ||
dose equivalent | sievert | Sv |
Multiples used with SI units
Name of multiple | Symbol | Value (multiply by) |
---|---|---|
atto | a | 10^{−18} |
femto | f | 10^{−15} |
pico | p | 10^{−12} |
nano | n | 10^{−9} |
micro | μ | 10^{−6} |
milli | m | 10^{−3} |
centi | c | 10^{−2} |
deci | d | 10^{−1} |
deca | da | 10 |
hecto | h | 10^{2} |
kilo | k | 10^{3} |
mega | M | 10^{6} |
giga | G | 10^{9} |
tera | T | 10^{12} |
peta | P | 10^{15} |
exa | E | 10^{18} |
SI units
SI units (Système International d'Unités)
Quantity | Name of unit | Symbol | Equivalent | Reciprocal |
---|---|---|---|---|
length | metre | m | 3.281 feet | 1 ft = 0.3048 m |
mass | kilogram | kg | 2.2 pounds | 1 lb = 0.454 kg |
time | second | s | ||
ampere | A | |||
thermodynamic temperature | kelvin | K | 1°C = 1.8°F | 1°C = 1 K |
luminous intensity | candela | cd | ||
amount of substance | mole | mol |
Supplementary units
Quantity | Unit | Symbol |
---|---|---|
plane angle | radian | rad |
solid angle | steradian | sr |
Derived SI units
Quantity | Name of unit | Symbol | Equivalent | Reciprocal |
---|---|---|---|---|
frequency | hertz | Hz | ||
energy | joule | J | 0.2388 calories | 1 cal = 4.1868 J |
force | newton | N | 0.225 pounds force | 1 lbf = 4.448 N |
power | watt | W | 0.00134 horse power | 1 hp = 745.7 W |
pressure | pascal | Pa | 0.00689 pounds force/sq.inch | 1 lbf/sq.in = 145 Pa |
electric charge | coulomb | C | ||
electric potential difference | volt | V | ||
electric resistance | ohm | Ω | ||
electric conductance | siemens | S | ||
electric capacitance | farad | F | ||
weber | Wb | |||
inductance | henry | H | ||
magnetic flux density | tesla | T | ||
luminous flux | lumen | lm | ||
illuminous | lux | lx | ||
absorbed dose | gray | Gy | ||
activity | becquerel | Bq | ||
dose equivalent | sievert | Sv |
Multiples used with SI units
Name of multiple | Symbol | Value (multiply by) |
---|---|---|
atto | a | 10^{−18} |
femto | f | 10^{−15} |
pico | p | 10^{−12} |
nano | n | 10^{−9} |
micro | μ | 10^{−6} |
milli | m | 10^{−3} |
centi | c | 10^{−2} |
deci | d | 10^{−1} |
deca | da | 10 |
hecto | h | 10^{2} |
kilo | k | 10^{3} |
mega | M | 10^{6} |
giga | G | 10^{9} |
tera | T | 10^{12} |
peta | P | 10^{15} |
exa | E | 10^{18} |
SI units
SI units (Système International d'Unites) Internationally agreed system of units, derived from the mks (metre, kilogram, and second) system. SI units are now used for many scientific purposes, and have replaced the fps (foot, pound, and second) and cgs (centimetre, gram, and second) systems. The seven basic units are: the metre (m) for length, kilogram (kg) for mass, second (s) for time, ampere (A) for electrical current, Kelvin (K) for temperature, mole (mol) for amount of substance, and candela (cd) for luminous intensity.
Measurement | Unit | Symbol |
---|---|---|
Basic units | ||
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 |
Supplementary units | ||
Plane angle | radian | rad |
Solid angle | steradian | sr |
Derived units | ||
Frequency | hertz | Hz |
Force | newton | N |
Pressure, stress | pascal | Pa |
Work (energy, heat) | joule | J |
Power | watt | W |
coulomb | C | |
Electromotive force | volt | V |
Electric resistance | ohm | 1/2 |
Electric conductance | siemens | S |
Electric capacitance | farad | F |
Inductance | henry | H |
Magnetic flux | weber | Wb |
Magnetic flux density | tesla | T |
Illuminance | lux | lx |
Luminous flux | lumen | lm |
röntgen | r | |
Radiation activity | becquerel | Bq |
Radiation absorbed dose | gray | Gy |
Radiation dose equivalent | sievert | Sv |
Celsius temperature | °Celsius | °C |
SI units
SI units (Système International d'Unités) The international system of units of measurement which evolved over a number of years from the m.k.s. system (based on the metre, kilogram, and second) and was finally adopted in 1960 by the 11th Conférence Générale des Poids et Mesures. The system is widely used in trade and is recommended for all scientific work. There are seven basic units: metre (m, length); kilogram (kg, mass); second (s, time); ampere (A, electric current); kelvin (K, thermodynamic temperature); candela (cd, luminous intensity); and mole (mol, amount of substance). There are also two supplementary units: radian (rad, plane angle); and steradian (sr, solid angle). From these, a further 18 units are derived: hertz (Hz, frequency); joule (J, energy); newton (N, force); watt (W, power); pascal (Pa, pressure); coulomb (C, electric charge); volt (V, electric potential); ohm (Ω, electric resistance); siemens (S, electric conductance); farad (F, electric capacitance); weber (Wb, magnetic flux); tesla (T, magnetic induction); lumen (lm, luminous flux); lux (lx, illuminance); gray (Gy, absorbed radiation dose); becquerel (Bq, radioactivity); and sievert (Sv, radiation dose equivalent). See Derived SI units.
SI Units (Système international d'unités)
Quantity | Name of unit | Symbol | Equivalent | Reciprocal |
---|---|---|---|---|
length | metre | m | 3.281 feet | 1 ft = 0.3048 m |
mass | kilogram | kg | 2.2 pounds | 1 lb = 0.454 kg |
time | second | s | ||
ampere | A | |||
thermodynamic temperature | kelvin | K | 1°C = 1.8°F | 1°C = 1 K |
luminous intensity | candela | cd | ||
amount of substance | mole | mol |
Supplementary units
Quantity | Unit | Symbol |
---|---|---|
plane angle | radian | rad |
solid angle | steradian | sr |
SI units
SI units The system of units of measurement adopted internationally for scientific and technical use under the Système International d'Unités. There are seven fundamental units – the meter, second, kilogram, ampere, kelvin, candela, and mole – of seven dimensionally independent physical quantities. Other units are derived algebraically from these base units without the use of numerical factors, or are dimensionless (like the radian). The symbols for all units are standardized, as are the prefixes (and their symbols) that represent decimal multiples (e.g. nano-, micro-, milli-, kilo-, mega-, giga-) of the units.