A question about portion sizes

I work out regularly, doing both cardio and resistance exercises and as a result I have a very healthy appetite. My diet is generally healthy and well balanced but If Im honest, my portions are probably slightly larger than necessary! I like the concept of eating little and often...such as the 5-6 small meals per day but Im unsure about what would be classed as a "small meal"! Are we talking say a 'nuts (handful) and piece of fruit' small or 'chicken breast salad' small etc? Or would a better guide be in terms of calaries and not size??? Im confused and cant seem to find any better explanation than "small" anywhere! Can anyone help?