I always use this company to compare delivery options for my parcels, just put in the size and weight and it gives you a range of possible options. It is easy to use and gives a range of companys, (including royal mail) and their prices. They also have an app to do this. Please make sure the size and weight information is correct, as i under measured a parcel and had to pay an extra £5.65 for getting it wrong! This was from the company i chose to deliver it, not parcel2go.