There is no fixed way to produce an estimate for work to be produced, but using knowledge with math's can be a powerful combination that allows you to minimize the risk of under pricing your projects as well as to make better decisions.
All project costs are a combination of your time and the use of required resources. Your ability to develop code and content quickly and efficiently is directly dependent on the quality of input you receive from the client, who in turn is dependent on their suppliers and partners. The situation is presented in the following diagram:
Your pricing method needs to reflect these factors that affect your ability to produce the end product. To recap, the following are the factors that your pricing calculation needs to incorporate:
How the client's input affects your software development performance.
How the client's input affects the costs incurred through using suppliers your suppliers and resources.