When should I use each temperature scale?

Use Celsius for daily life in most countries and general science, Fahrenheit for US weather and cooking, Kelvin for physics and chemistry calculations, and Rankine for engineering applications requiring absolute temperatures.

JavaScript Temperature Converter:

class TemperatureConverter {
  
  // Convert from Celsius
  static celsiusToFahrenheit(celsius) {
    return (celsius * 9/5) + 32;
  }
  
  static celsiusToKelvin(celsius) {
    return celsius + 273.15;
  }
  
  static celsiusToRankine(celsius) {
    return (celsius * 9/5) + 491.67;
  }
  
  static celsiusToReaumur(celsius) {
    return celsius * 4/5;
  }
  
  // Convert from Fahrenheit
  static fahrenheitToCelsius(fahrenheit) {
    return (fahrenheit - 32) * 5/9;
  }
  
  static fahrenheitToKelvin(fahrenheit) {
    return (fahrenheit - 32) * 5/9 + 273.15;
  }
  
  static fahrenheitToRankine(fahrenheit) {
    return fahrenheit + 459.67;
  }
  
  // Convert from Kelvin
  static kelvinToCelsius(kelvin) {
    return kelvin - 273.15;
  }
  
  static kelvinToFahrenheit(kelvin) {
    return (kelvin - 273.15) * 9/5 + 32;
  }
  
  static kelvinToRankine(kelvin) {
    return kelvin * 9/5;
  }
  
  // Convert from Rankine
  static rankineToCelsius(rankine) {
    return (rankine - 491.67) * 5/9;
  }
  
  static rankineToFahrenheit(rankine) {
    return rankine - 459.67;
  }
  
  static rankineToKelvin(rankine) {
    return rankine * 5/9;
  }
  
  // Universal converter function
  static convert(temperature, fromScale, toScale) {
    fromScale = fromScale.toLowerCase();
    toScale = toScale.toLowerCase();
    
    if (fromScale === toScale) {
      return temperature;
    }
    
    // Convert to Celsius first (as intermediate)
    let celsius;
    switch (fromScale) {
      case 'celsius':
      case 'c':
        celsius = temperature;
        break;
      case 'fahrenheit':
      case 'f':
        celsius = this.fahrenheitToCelsius(temperature);
        break;
      case 'kelvin':
      case 'k':
        celsius = this.kelvinToCelsius(temperature);
        break;
      case 'rankine':
      case 'r':
        celsius = this.rankineToCelsius(temperature);
        break;
      default:
        throw new Error(`Unknown temperature scale: ${fromScale}`);
    }
    
    // Convert from Celsius to target scale
    switch (toScale) {
      case 'celsius':
      case 'c':
        return celsius;
      case 'fahrenheit':
      case 'f':
        return this.celsiusToFahrenheit(celsius);
      case 'kelvin':
      case 'k':
        return this.celsiusToKelvin(celsius);
      case 'rankine':
      case 'r':
        return this.celsiusToRankine(celsius);
      default:
        throw new Error(`Unknown temperature scale: ${toScale}`);
    }
  }
  
  // Batch convert multiple temperatures
  static batchConvert(temperatures, fromScale, toScale) {
    return temperatures.map(temp => ({
      original: temp,
      converted: this.convert(temp, fromScale, toScale),
      fromScale,
      toScale
    }));
  }
  
  // Get temperature scale info
  static getScaleInfo(scale) {
    const scales = {
      celsius: {
        name: 'Celsius',
        symbol: '°C',
        freezingPoint: 0,
        boilingPoint: 100,
        description: 'Based on water freezing and boiling points'
      },
      fahrenheit: {
        name: 'Fahrenheit',
        symbol: '°F',
        freezingPoint: 32,
        boilingPoint: 212,
        description: 'Commonly used in the United States'
      },
      kelvin: {
        name: 'Kelvin',
        symbol: 'K',
        freezingPoint: 273.15,
        boilingPoint: 373.15,
        absoluteZero: 0,
        description: 'Absolute temperature scale used in science'
      },
      rankine: {
        name: 'Rankine',
        symbol: '°R',
        freezingPoint: 491.67,
        boilingPoint: 671.67,
        absoluteZero: 0,
        description: 'Absolute scale using Fahrenheit degrees'
      }
    };
    
    return scales[scale.toLowerCase()] || null;
  }
  
  // Check if temperature is physically possible
  static isValidTemperature(temperature, scale) {
    const celsius = this.convert(temperature, scale, 'celsius');
    return celsius >= -273.15; // Above absolute zero
  }
  
  // Format temperature with proper symbol
  static formatTemperature(temperature, scale, decimals = 2) {
    const scaleInfo = this.getScaleInfo(scale);
    if (!scaleInfo) return `${temperature} (unknown scale)`;
    
    return `${temperature.toFixed(decimals)}${scaleInfo.symbol}`;
  }
}

// Usage examples
console.log(TemperatureConverter.celsiusToFahrenheit(25)); // 77
console.log(TemperatureConverter.fahrenheitToCelsius(77)); // 25
console.log(TemperatureConverter.convert(100, 'celsius', 'kelvin')); // 373.15

// Batch conversion
const temps = [0, 20, 37, 100];
const converted = TemperatureConverter.batchConvert(temps, 'celsius', 'fahrenheit');
console.log(converted);
// [
//   { original: 0, converted: 32, fromScale: 'celsius', toScale: 'fahrenheit' },
//   { original: 20, converted: 68, fromScale: 'celsius', toScale: 'fahrenheit' },
//   ...
// ]
            

Python Temperature Converter:

class TemperatureConverter:
    """Comprehensive temperature conversion utility"""
    
    # Conversion constants
    ABSOLUTE_ZERO_CELSIUS = -273.15
    
    @staticmethod
    def celsius_to_fahrenheit(celsius: float) -> float:
        """Convert Celsius to Fahrenheit"""
        return (celsius * 9/5) + 32
    
    @staticmethod
    def fahrenheit_to_celsius(fahrenheit: float) -> float:
        """Convert Fahrenheit to Celsius"""
        return (fahrenheit - 32) * 5/9
    
    @staticmethod
    def celsius_to_kelvin(celsius: float) -> float:
        """Convert Celsius to Kelvin"""
        return celsius + 273.15
    
    @staticmethod
    def kelvin_to_celsius(kelvin: float) -> float:
        """Convert Kelvin to Celsius"""
        return kelvin - 273.15
    
    @staticmethod
    def fahrenheit_to_kelvin(fahrenheit: float) -> float:
        """Convert Fahrenheit to Kelvin"""
        celsius = TemperatureConverter.fahrenheit_to_celsius(fahrenheit)
        return TemperatureConverter.celsius_to_kelvin(celsius)
    
    @staticmethod
    def kelvin_to_fahrenheit(kelvin: float) -> float:
        """Convert Kelvin to Fahrenheit"""
        celsius = TemperatureConverter.kelvin_to_celsius(kelvin)
        return TemperatureConverter.celsius_to_fahrenheit(celsius)
    
    @classmethod
    def convert(cls, temperature: float, from_scale: str, to_scale: str) -> float:
        """Universal temperature conversion"""
        from_scale = from_scale.lower()
        to_scale = to_scale.lower()
        
        if from_scale == to_scale:
            return temperature
        
        # Conversion mapping
        conversions = {
            ('celsius', 'fahrenheit'): cls.celsius_to_fahrenheit,
            ('celsius', 'kelvin'): cls.celsius_to_kelvin,
            ('fahrenheit', 'celsius'): cls.fahrenheit_to_celsius,
            ('fahrenheit', 'kelvin'): cls.fahrenheit_to_kelvin,
            ('kelvin', 'celsius'): cls.kelvin_to_celsius,
            ('kelvin', 'fahrenheit'): cls.kelvin_to_fahrenheit,
        }
        
        # Direct conversion if available
        conversion_key = (from_scale, to_scale)
        if conversion_key in conversions:
            return conversions[conversion_key](temperature)
        
        # Multi-step conversion through Celsius
        if from_scale not in ['celsius', 'fahrenheit', 'kelvin']:
            raise ValueError(f"Unsupported scale: {from_scale}")
        if to_scale not in ['celsius', 'fahrenheit', 'kelvin']:
            raise ValueError(f"Unsupported scale: {to_scale}")
        
        # Convert to Celsius first, then to target
        if from_scale != 'celsius':
            temperature = conversions[(from_scale, 'celsius')](temperature)
        
        if to_scale != 'celsius':
            temperature = conversions[('celsius', to_scale)](temperature)
        
        return temperature
    
    @classmethod
    def batch_convert(cls, temperatures: list, from_scale: str, to_scale: str) -> list:
        """Convert multiple temperatures"""
        results = []
        for temp in temperatures:
            try:
                converted = cls.convert(temp, from_scale, to_scale)
                results.append({
                    'original': temp,
                    'converted': converted,
                    'from_scale': from_scale,
                    'to_scale': to_scale
                })
            except Exception as e:
                results.append({
                    'original': temp,
                    'error': str(e),
                    'from_scale': from_scale,
                    'to_scale': to_scale
                })
        return results
    
    @classmethod
    def is_valid_temperature(cls, temperature: float, scale: str) -> bool:
        """Check if temperature is physically possible (above absolute zero)"""
        try:
            celsius = cls.convert(temperature, scale, 'celsius')
            return celsius >= cls.ABSOLUTE_ZERO_CELSIUS
        except:
            return False
    
    @staticmethod
    def get_reference_points():
        """Get common temperature reference points"""
        return {
            'absolute_zero': {'celsius': -273.15, 'fahrenheit': -459.67, 'kelvin': 0},
            'water_freezing': {'celsius': 0, 'fahrenheit': 32, 'kelvin': 273.15},
            'room_temperature': {'celsius': 20, 'fahrenheit': 68, 'kelvin': 293.15},
            'body_temperature': {'celsius': 37, 'fahrenheit': 98.6, 'kelvin': 310.15},
            'water_boiling': {'celsius': 100, 'fahrenheit': 212, 'kelvin': 373.15}
        }
    
    @staticmethod
    def format_temperature(temperature: float, scale: str, decimals: int = 2) -> str:
        """Format temperature with appropriate symbol"""
        symbols = {
            'celsius': '°C',
            'fahrenheit': '°F',
            'kelvin': 'K'
        }
        
        symbol = symbols.get(scale.lower(), f' {scale}')
        return f"{temperature:.{decimals}f}{symbol}"

# Usage examples
converter = TemperatureConverter()

# Basic conversions
print(converter.celsius_to_fahrenheit(25))  # 77.0
print(converter.fahrenheit_to_celsius(77))  # 25.0
print(converter.celsius_to_kelvin(25))      # 298.15

# Universal conversion
print(converter.convert(100, 'celsius', 'fahrenheit'))  # 212.0
print(converter.convert(0, 'kelvin', 'celsius'))        # -273.15

# Batch conversion
temps = [0, 25, 100]
results = converter.batch_convert(temps, 'celsius', 'fahrenheit')
for result in results:
    print(f"{result['original']}°C = {result['converted']}°F")

# Reference points
refs = converter.get_reference_points()
print("Water boiling point:", refs['water_boiling'])

# Validation
print(converter.is_valid_temperature(-300, 'celsius'))  # False
print(converter.is_valid_temperature(25, 'celsius'))    # True