Thanks for your interest in our furniture!
All of our cribs will fit a standard size mattress. We are required by law to manufacture according to specific standards. Some mattresses will fit more snug than others so for the absolute best fit, we recommend our Sleepwell Mattresses. You can find our more information here about them: http://www.milliondollarbaby.com/Sleepwellmattresses
You can also purchase directly from us here:
The interior dimensions for our cribs are approximately: 52.375 x 28".
The approximate interior dimensions for our mini cribs are: 37.625 x 23.625".
Please let me know if you have any more questions. We are always here to help!
The MDB Family