My arms looks smaller, but actually are bigger than other guys. Why?

I’ve been working out since October and my arms have gone up to 14.8inches and 15.25 after a workout. What I find interesting is when I compare my arm relaxed compared to my friends, their arms look bigger even though they don’t work out, but when it comes down to measuring it, my arms are up to 1.5 inches bigger. What’s up with this illusion?
Here’s a link to my pics to give you a better picture of what I’m working with: http://forum.bodybuilding.com/photo/showgallery.php?ppuser=2708603&cat=500

Probably has to do with how they’re proportioned to their bodies. If the rest of their arm is smaller, their muscles will appear bigger. Thats why people with really long arms dont get that defined peak, their bicep muscle is too long to make that shape

Also, everyone is built differently. So your relaxed muscle on your arm may not look the same as your friends, but if he were to have the same amount of muscle as you on his arms they would probably be bigger, hence the size difference when you contract your bicep

Teen Bodybuilder (New Camera)