Is there a formula to calculate the fiat value of a Satoshi using your fiat principle?
The number of satoshi per bitcoin is
100,000,000, so if you have a fiat value per bitcoin such as
$7000/BTC, the calculation is:
$/satoshi = $7000/1e8 = $0.00007 per satoshi
Of course, there is no fixed fiat to satoshi value because the fiat value of Bitcoin is determined by the market, i.e. exchange value.