Post on Medial

Every speaker, mentor, and founder suggests doing market research. You need to understand how to conduct market research properly. The internet is flooded with information, but secondary market research will not give you a clear picture unless it is done by a professional. Therefore, you need to get on the ground if you have any idea. People will eventually tell you what they want. If you take too long to do research, you will either become discouraged or miss the opportunity.

Gap identification and how intense the painpoint is pluse the pocket of customer can give a pretty clear picture about the market availability

Make an innovative, useful yet scrappy MVP if it gains slight traction you'll know you're on the right path

Talk to 100 people you will get the idea

Read about reviews of your potential competitors and understand what their customers are complaining about. If you can solve it then you are on the right track to build a new product.

Every industry has thousands of products and services so it's very hard to find any particular product market size so if you wants to know the real market size then you can conduct some type of research in a regional level or international level but it's a very time consuming things. I think you should start working with roughly estimated market size

You can conduct surveys amongst the group of possible customers of your startup to get an idea about their feedback/requirement.

Research.