## List of symbols

Unit for calculation | |||

Symbol | Meaning | Metric | Imperial |

A_{C} |
Surface area of heating conductor | cm^{2} |
in^{2} |

b | Width (ribbon or strip) | mm | in |

C_{t} |
Temperature factor (ratio of resistivity at operating temperature to resistivity at room temperature) | ||

d | Wire diameter | mm | in |

D | Outer coil diameter | mm | in |

I | Current | A | A |

L | Length of heating conductor | m | ft |

L_{e} |
Coil length | mm | in |

n | Number of turns | ||

p | Surface load of heating element | W/cm^{2} |
W/in^{2} |

P | Power | W | W |

q | Cross-sectional area of heating conductor | mm^{2} |
in^{2} |

r | Relative pitch | ||

R_{T} |
Resistance at working temperature | Ω | Ω |

R_{20} |
Resistance at room temperature (20°C, 68°F) | Ω | Ω |

s | Pitch | mm | in |

t | Thickness (ribbon or strip) | mm | in |

T | Temperature | K, °C | K, °F |

U | Voltage | V | V |

α | Temperature coefficient of resistivity | K^{-1} |
°F^{-1} |

γ | Density (old marking) | g/cm^{3} |
lb/in^{3} |

ρ | Resistivity | Ω mm^{2}/m |
Ω/smf /cmf* |

10 | Balancing factor used in the formulas makes possible that the values can be used with units of section 1: e.g. wire diameter, d, in millimeter (mm) or inch (in) is different from length of heating conductor, l, in meter (m) or foot (ft) |