The Scalepath 
Market Sizing Framework is a clear, easy-to-follow 
bottoms-up TAM model template for Excel. And it's free.
While this framework is SaaS-focused, you can adapt it to suit any B2B business. It's the very same framework we use as a foundational part of our 
TAM software and for our clients. It provides a structure for your 
TAM, SAM, and SOM model.  
In this Excel download, you'll customize your model in the following key areas: