Oh right, thank you for your help !

IRCs are like vouchers in a sense, they're exchanged for stamps at post offices. You don't have to attach them onto the SASE, you just put them in your envelope along with the SASE, letter, photo, etc.

As for how many you'll need, you'll really have to know the weight to get an accurate answer. Generally speaking, a 8x10 in a plain manila envelope can fall either just below 1oz or just over it depending on the photo paper and envelope used. If it's under, 2 IRCs will cover it, if over, then you'll need 3.

I'll also add that if you plan to send to the US often, it's more economical to purchase American stamps rather than using IRCs. IRCs are often valued much less than what they cost to buy.

This is the first time I'm trying the international sending & I'm a little confused with IRC's. I understand you need a letter, photo & SASE to send but with the IRC's, how do you know how many you will need to buy for a return from the USA to UK of just an 8x10?. How do you find out the weight to match up with the cost per IRC? and can you go to the post office with your letter, purchase the IRC's from them, attach them to your SAE, seal your mail & then ask them to weigh it? & then they send it off for you.

Thank you for all your help!