Yes they get bigger when the bombs get bigger, especially a 4k egg. But it also depends on what purpose the bomb itself.
General Purpose which about 50-percent of the bomb is explosive materials and weigh between 500 and 2,000 pounds do blast and fragmentation effects and the casing is about one half inch thick
Fragmentation which only roughly 10-20% of the bombs weight is explosive and the casing is scored so that it breaks into pieces. THis of course causes the high speed frag which does the damage.
Penatrator's whcih have about 25-30% of the bombs weight is explosive and the forward end of the bomb is usually solid steel so it will not crush on impact, because if it did this it does not cause the correct effect for the blast. Bunker busters/JDAM's (modern), which are usually a 2k egg can penatrate cement 7-9 feet thick.
One of the modern day bombs, a GBU-39 has only 50lbs of explosives and weighs only 250lbs has a blast radius of about 26ft in diameter, (compaired to a 2k bomb that makes a blast of about 80+ft), and makes this nice picture... yes that is steel reinforced concrete, six feet of it.
And like Stoney said it all depends on what type of fuze was being used. If it was an air-burst, it will basically just flatten everything from the blast, frag and shockwave. If it is a ground burst it moves alot of dirt and makes a nice size hole.
I can't remember exactly, but from my memory from a few years ago, a 500lb bomb made a crater approximately 2 to 4 feet around, and approximately 6-12 inches deep. A 2000 lb bomb made a crater that was approx. 8-10 feet around, and a little over 1 foot deep.
If the above was the case... it must have been a dud...
Here is a video of a 500lb bomb dropped in Fallujah...
500lb And another one... (about the 2 minute mark it hits)
Bye Building Just my knowledge of working with them...