How much is 3 oz of chicken / fish?

I am having a difficult time estimating portion sizes. 

Given that the serving size for chicken and fish area usually 3 oz, how can I measure this?  I think that 1/2 a pound of fish is about 8 oz, but I am not sure.  How many oz is a normal to large chicken breast?  Thanks.

3 oz is supposed to be about the size of a deck of cards.  Ultimately, I would recommend purchasing a cheap food scales (less than $10) until you can accurately determine what a serving size should be.  Our portions are so skewed as portions have gotten larger and larger.  To me, what I used to think was a normal chicken breast, is about 6-8oz.

One way to know your portion size when it comes to fish/chicken is to look at your hand. Your whole hand is the portion size for fish and for chicken it's the size of your palm. That's what I do when I go out to eat and I box the rest ;)

litadoll, those are good guidelines (the palm and hand) but for chicken it doesn't work as well.  The trouble I've had with chicken is that it's very thick so a piece of chicken that is slightly longer than my palm ends up being 8 ounces.   I echo poster #1, you really have to find a cheap food scale.   When I first started this site I was estimating my chicken only to find out that what I *thought* was 4 ounces was in reality 8 ounces.  

The only other help I can offer is that chicken breasts are usually measured in halves, which confused me.  I thought "okay, when I buy an entire chicken, there's a breast on one side of the bone and a breast on the other side so I must be eating 1/2 breast if I eat everything on one side of the bone."   Nope!   That's considered a FULL breast so basically for 1/2 breast (which runs about 3-4 ounces) it should be one quarter of what you picture as the ENTIRE chicken's breasts.  Does that make sense?? ;o)