pip values

Pip value of pairs like GBP/USD or EUR/USD is always $10 for a standard lot, but is a weird number, that changes, for pairs like USD/JPY or EUR/GBP ... is there a mathematical formula so I can calculate that value, instead of looking it up every time?

Of course there is. For USD/JPY you have to divide it by the current USD/JPY Ask price (because you have to buy USD with the JPY which you get for positions in USD/JPY), but normalized by 100 because of the difference in the amount of digits in EUR/USD and USD/JPY. For EUR/GBP positions you get pounds, so you have to multiply the usual price of the pip by the current GBP/USD Bid price.

But if you don't want to calculate that manually all the time you can google for
"pip value calculator" - there are plenty of free on-line and off-line calculators available to do this work for you.