Hi Driton, There is not enough information in your question to have the correct answer.
You will have to tell what type of steel it is, also what is this plate getting attached to as that can have an effect on the over all answer. What is the plate for as then you will need to bring F.O.S into the equation and also the what you are willing to pay for the cost of the bolts all this comes into the design.
I have attached a sheet with the workings on it and took it as a ( 4.8 ) with F.O.S @ ( 1.2 ) and DIA - 5 mm. I have also 2 charts relating to information for bolts that I took the information required.
It has been done as a rough guide so you know how to do the calculations when you get the relevant information required to solve your problem
I hope this helps you a little with your problem, Good luck :)