PayPal levies various charges at different rates, depending on where you live, when you send payments to or receive payments from others. Here is a PayPal fee calculator that will help you calculate these fees before you carry forward the transaction.
The PayPal Fee Calculator written by Ryan Olbe lets you calculate how much fees you have to pay when you receive payments from others. When a sender makes a payment, he decides who pay this fee. The sender may choose to pay the fee himself or herself or entrust the burden upon you. If the sender decides that you are the one who should pay the fee, then you have to pay at 2.9% + $0.30 of the total transaction. If the payment comes from overseas, the rates increase to 3.9% + $0.30.
There is also a reverse calculator. Say you want to know how much to send (or receive) so that exactly $100 ends up at the other account. The reverse calculator will tell. The advanced version of the calculator can take into account transactions involving multiple currencies.
For calculating eBay fees when putting up your items on auction, the eBay calculators at AuctionfeeCalculator will help. eBay calculators for different countries are listed on this site. Just choose the one where you intend to list your item and calculate the fees for various listing options. There are fees for posting additional pictures, using highlights for visibility, using templates and so on. The calculator also takes into account PayPal fees if you intend to pay using your PayPal account.