How do I determine what a pip is worth?

I have been doing a little demo trading and have noticed that my pip calculations are off.

Here is the equation I am using:

(Amount to risk)/(difference between enter price and stop*pip value)

This gives me the number of lots to use. Only problem is that I am having trouble determining the value of a pip. How is the best way to go about this? I'm using Metatrader, but it would be best if I knew how to calculate this on my own.

Thanks,

let's suppose your account is denominated in USD.

generally pipvalue in the quote currency = lotsize * pipsize

there are three possibilities:

1) you trade a pair where USD is the base currency like USD/XXX

pipvalue in $ = pipvalue / [USD/XXX]
example for USD/JPY:
USD/JPY = 116.50, lotsize = 100000, pipsize = 0.01
pipvalue = 100000 * 0.01 = 1000 Yen
pipvalue in $ = 1000 / 116.50 = 8.58 $

2) you trade a pair where USD is the quote currency like XXX/USD

pipvalue in $ = pipvalue
example for EUR/USD:
EUR/USD = 1.2750 (does not matter), lotsize = 100000, pipsize = 0.0001
pipvalue = 100000 * 0.0001 = 10$

3) you trade a cross like XXX/YYY

pipvalue in $ = pipvalue / [USD/YYY] OR pipvalue * [YYY/USD] (depending on the pairs avilable)

example EUR/JPY:
EUR/JPY = 149.50 (does not matter), USD/JPY = 116.50, lotsize = 100000, pipsize = 0.01
pipvalue = 100000 * 0.01 = 1000 Yen
pipvalue in $ = 1000 / 116.50 = 8.58 $