The single best way to make a market demand forecast is to think about market size and mind share at the same time. Market size looks at macroeconomic trends, like who needs your product or service and who has the money to pay. Mind share looks at micro-economic trends, like who is aware of your company and how your business is perceived as a comparative value. You can put together the market size/macroeconomic trends from the industry reports available on Manta. The mind share/micro-economic factors, however, are probably going to be up to you to figure out. Still, Manta gives you head start at a relatively low cost.