Cutting into this fabric made me cry.  Don't make me cry for nothing, purchase this bag so it was all worth it!
Messenger bag finished size is 16" width x 12" height x 4" depth 
Large full-width pocket - finished size is 15" wide x 9 ½ " tall (fits laptop)
Small Pocket (Phone Pocket) - finished size is 6 ½" tall x 6" wide