Temperature conversion

my %scale =
    Celcius    => { factor => 1  , offset => -273.15 },
    Rankine    => { factor => 1.8, offset =>    0    },
    Fahrenheit => { factor => 1.8, offset => -459.67 },
;
 
my $kelvin = +prompt "Enter a temperature in Kelvin: ";
die "No such temperature!" if $kelvin < 0;
 
for %scale.sort {
    printf "%12s: %7.2f\n", .key, $kelvin * .value<factor> + .value<offset>;
}

Output:

Enter a temperature in Kelvin: 21
     Celcius: -252.15
  Fahrenheit: -421.87
     Rankine:   37.80

Alternative version that accepts the input in any of the four scales:

while my $answer = prompt 'Temperature: ' {
    my $k = do given $answer {
        when s/:i C $// { $_ + 273.15 }
        when s/:i F $// { ($_ + 459.67) / 1.8 }
        when s/:i R $// { $_ / 1.8 }
        when s/:i K $// { $_ }
        default         { $_ }
    }
    say "  { $k }K";
    say "  { $k - 273.15 }℃";
    say "  { $k * 1.8 - 459.67 }℉";
    say "  { $k * 1.8 }R";
}

Output:

Temperature: 0
  0K
  -273.15℃
  -459.67℉
  0R
Temperature: 0c
  273.15K
  0℃
  32℉
  491.67R
Temperature: 212f
  373.15K
  100℃
  212℉
  671.67R
Temperature: -40c
  233.15K
  -40℃
  -40℉
  419.67R