Read the signs
Describe factors and trends affecting your industry and consider their implications for your business. Issues to think about include:
Based on the factors and trends you've described, what's the outlook for your industry for the next 3 to 5 years?
Once you understand your market, you can define your place in it.
Imagine you have no competition, and your customers' only option is to buy your product or service. How many customers would you have? How much money would your business make? That's the size of your market.
When estimating the size of your market, consider industry factors and trends, and pay special attention to those you think present special opportunities or challenges for your business.
Focus on what's right for your business and consider doing some research at GDSourcing. If you can, quantify your market in terms of dollars in sales.
If you can't find the exact information you're looking for, work with what you know.