# What are units

## General information and resources

Base sizeBase unitSurnamesymbolSurnamesymboldefinitiontime\ (t \)second\ (\ rm {s} \)The second, symbol \ (\ rm {s} \), is the SI unit of time. It is defined by the fixed numerical value for the radiation frequency of the cesium atom \ (\ Delta {\ nu _ {{\ rm {Cs}}}} \ (9 \, 192 \, 631 \, 770 \, \) frac {1} {{\ rm {s}}} \). With this definition we get \ [1 \, {\ rm {s}} = \ frac {{9 \, 192 \, 631 \, 770}} {{\ Delta {\ nu _ {{\ rm {Cs}} }}}} \]length\ (l \)meter\ (\ rm {m} \)The meter, symbol \ (\ rm {m} \), is the SI unit of length. It is defined by the fixed numerical value for the speed of light in a vacuum \ (c \) of \ (299 \, 792 \, 458 \, \ frac {\ rm {m}} {\ rm {s}} \), where the Second is defined by the constant \ (\ Delta {\ nu _ {{\ rm {Cs}}}} \). With this definition, \ [1 \, {\ rm {m}} = \ frac {c} {{299 \, 792 \, 458}} \, \ frac {1} {\ rm {s}} \] or \ [1 \, {\ rm {m}} = \ frac {{9 \, 192 \, 631 \, 770}} {{299792458}} \ cdot \ frac {c} {{\ Delta {\ nu _ {{\ rm {Cs}}}}}}} \] or \ [1 \, {\ rm {m}} \ approx 30 {,} 663 \, 319 \ cdot \ frac {c} {{\ Delta {\ nu _ {{\ rm {Cs}}}}}} \]Dimensions\ (m \)kilogram\ (\ rm {kg} \)The kilogram, symbol \ (\ rm {kg} \), is the SI unit of mass. It is defined by the fixed numerical value for the PLANCK constant \ (h \) of \ (6 {,} 626 \, 070 \, 15 \ cdot {10 ^ {- 34}} \, \ frac {\ rm {kg } \, \ rm {m} ^ 2} {\ rm {s}} \), where the meter and the second are represented by the constants \ (c \) and \ (\ Delta {\ nu _ {{\ rm {Cs }}}} \) are defined. With this definition we get \ [1 \, {\ rm {kg}} = \ frac {h} {{6 {,} 626 \, 070 \, 15 \ cdot {{10} ^ {- 34}}}} \, \ frac {{\ rm {s}}} {{{{\ rm {m}} ^ 2}}} \] or \ [1 \, {\ rm {kg}} = \ frac {{{ {\ left ({{\ rm {299 \, 792 \, 458}}} \ right)} ^ 2}}} {{6 {,} 626 \, 070 \, 15 \ cdot {{10} ^ {- 34}} \ cdot {\ rm {9 \, 192 \, 631 \, 770}}}} \ cdot \ frac {{h \ cdot \ Delta {\ nu _ {{\ rm {Cs}}}}}} {{{c ^ 2}}} \] or \ [1 \, {\ rm {kg}} \ approx 1 {,} 475 \, 521 \, 4 \ cdot {10} ^ {40} \ cdot \ frac {{h \ cdot \ Delta {\ nu _ {{\ rm {Cs}}}}}}} {{{c ^ 2}}} \]electric current\ (I \)amp\ (\ rm {A} \)The ampere, symbol \ (\ rm {A} \), is the SI unit of electrical current. It is defined by the fixed numerical value for the elementary charge \ (e \) of \ (1 {,} 602 \, 176 \, 634 \ cdot 10 ^ {- 19} \, \ rm {A} \, \ rm {s } \), where the second is defined by the constant \ (\ Delta {\ nu _ {{\ rm {Cs}}}} \). With this definition we get \ [1 \, {\ rm {A}} = \ frac {{e}} {1 {,} 602 \, 176 \, 634 \ cdot 10 ^ {- 19}} \, \ frac {1} {\ rm {s}} \] or \ [1 \, {\ rm {A}} = \ frac {1} {{9 \, 192 \, 631 \, 770 \ cdot 1 {,} 602 \, 176 \, 634 \ cdot {{10} ^ {- 19}}}} \ cdot e \ cdot \ Delta {\ nu _ {{\ rm {Cs}}}} \] or \ [1 \ , {\ rm {A}} \ approx 6 {,} 789 \, 687 \ cdot {10 ^ 8} \ cdot e \ cdot \ Delta {\ nu _ {{\ rm {Cs}}}} \]temperature\ (T \)Kelvin\ (\ rm {K} \)The Kelvin, symbol \ (\ rm {K} \), is the SI unit of the thermodynamic temperature. It is defined by the fixed numerical value for the BOLTZMANN constant \ (k _ {\ rm {B}} \) of \ (1 {,} 380 \, 649 \ cdot 10 ^ {- 23} \, \ frac {{{ \ rm {kg}} \, {{\ rm {m}} ^ 2}}} {{{{{\ rm {s}} ^ 2} \, {\ rm {K}}}} \), where the Kilogram, the meter and the second are defined by the constants \ (h \), \ (c \) and \ (\ Delta {\ nu _ {{\ rm {Cs}}}} \). With this definition we get \ [1 \, {\ rm {K}} = \ frac {{1 {,} 380 \, 649 \ cdot {{10} ^ {- 23}}}} {k _ {\ rm { B}}} \, \ frac {{{\ rm {kg}} \, {{\ rm {m}} ^ 2}}} {{{{{\ rm {s}} ^ 2}}} \] or . \ [1 \, {\ rm {K}} = \ frac {{1 {,} 380 \, 649 \ cdot {{10} ^ {- 23}}}} {{6 {,} 626 \, 070 \, 15 \ cdot {{10} ^ {- 34}} \ cdot 9 \, 192 \, 631 \, 770}} \ cdot \ frac {{\ Delta {\ nu _ {{\ rm {Cs}}} } \ cdot h}} {k _ {\ rm {B}}} \] or \ [1 \, {\ rm {K}} \ approx 2 {,} 266 \, 665 \, 3 \ cdot \ frac { {\ Delta {\ nu _ {{\ rm {Cs}}}} \ cdot h}} {k _ {\ rm {B}}} \]Amount of substance\ (n \)Mole\ (\ rm {mol} \)The amount of substance, symbol \ (n \), of a system is a measure of the number of specified elementary individual parts. A specified elementary part can be an atom, a molecule, an ion, an electron or another particle or group of particles.
The mole, symbol \ (\ rm {mol} \), is the SI unit for the amount of substance. A mole contains exactly \ (6 {,} 022 \, 140 \, 76 \ cdot {10 ^ {23}} \) specified elementary parts. This number is the fixed numerical value for the AVOGADRO constant \ (N _ {\ rm {A}} \) of \ (6 {,} 022 \, 140 \, 76 \ cdot {10 ^ {23}} \, \ frac {1} {\ rm {mol}} \) and is called the AVOGADRO number. With this definition we get \ [1 \, {\ rm {mol}} = \ frac {{6 {,} 022 \, 140 \, 76 \ cdot {{10} ^ {23}}}} {{{N_ {\ rm {A}}}}} \]Light intensity\ (I _ {\ rm {v}} \)Candela\ (\ rm {cd} \)The candela, symbol \ (\ rm {cd} \), is the SI unit of the light intensity in a given direction. It is defined by the fixed numerical value for the photometric radiation equivalent \ (K _ {\ rm {cd}} \) of \ (633 \, \ frac {{{\ rm {cd}} \, {\ rm {sr}} \ , {{\ rm {s}} ^ 3}}} {{{\ rm {kg}} \, {{\ rm {m}} ^ 2}}} \), where the kilogram, the meter and the second are defined by the constants \ (h \), \ (c \) and \ (\ Delta {\ nu _ {{\ rm {Cs}}}} \). With this definition we get \ [1 \, {\ rm {cd}} = \ frac {{{K _ {{\ rm {cd}}}}}} {{633}} \, \ frac {{{\ rm {kg}} \, {{\ rm {m}} ^ 2}}} {{{{\ rm {s}} ^ 3} \, {\ rm {sr}}}} \] or \ [1 \, {\ rm {cd}} = \ frac {1} {{6 {,} 626 \, 070 \, 15 \ cdot {{10} ^ {- 34}} \ cdot {{\ left ({9 \ , 192 \, 631 \, 770} \ right)} ^ 2} \ cdot 683}} \ cdot {\ left ({\ Delta {\ nu _ {{\ rm {Cs}}}}} \ right) ^ 2 } \ cdot h \ cdot {K _ {{\ rm {cd}}}} \] or \ [1 \, {\ rm {cd}} \ approx {\ rm {2 {,} 614 \, 830}} \ cdot {10 ^ {10}} \ cdot {\ left ({\ Delta {\ nu _ {{\ rm {Cs}}}}} \ right) ^ 2} \ cdot h \ cdot {K _ {{\ rm {CD}}}}\]