The size of safe you will need will be dependent on what you are going to put in it. The quickest way to decide this is to find the largest item you plan to store and measure its dimensions. You should then factor in 25% more room in your security safe. You should also note that because the outside of a safe may seem large, the inside can be much smaller. This is due to the security and insulation in the walls of the security safe. Where possible you should make sure you check the internal measurements of any safe you intend to buy. Your extra 25% will also allow for any extra items you plan to store. If it's likely that you will acquire more valuables over time you should get the biggest safe you can afford.