How do I estimate market size?

How do I estimate market size is mainly about calculating the number of potential buyers or transactions and their realistic annual spending. A reliable approach is to use top-down and bottom-up methods while defining geography, segment, use case, time period, price, purchase frequency, and adoption. For example, a bottom-up estimate can multiply eligible businesses by problem prevalence, expected penetration, and annual contract value. The main caution is that broad industry totals often include unrelated products, geographies, and customers, so assumptions must be transparent. The final output should provide a credible market-size range with formulas, sources, sensitivities, and a distinction between theoretical and reachable revenue.