When purchasing area rugs for a bedroom you want to bring into account whether you want the rug to accommodate both the bed and side tables or just the bed alone. This will help you to determine how large or small your rug needs to be. Measuring the space that you want covered beforehand can also help you to determine which size would be most appropriate.
Tip: So as long as your feet touches the rugs on both sides while stepping out of bed, the size is good enough. 2'-3' on either side should suffice.