---
title: "Building a bottom-up market estimate"
course: "ENTR 242 · Start your own business"
unit: "Market attractiveness and go-to-market"
lesson: 30 of 43
source: https://open.maestrocollege.edu/start-your-own-business/building-a-bottom-up-market-estimate
publisher: Maestro College
---

# Building a bottom-up market estimate

Lesson 30 of 43 in **Start your own business** (ENTR 242), unit "Market attractiveness and go-to-market". An open lesson from Maestro College.

## What the learner will be able to do
- Create a bottom-up TAM, SAM and SOM estimate with every assumption and its source written down.
- Judge market attractiveness by weighing size, growth, reachability, pain severity and competition, not headline size alone.

## Teaching notes
Scenario: GearShare, a peer-to-peer app where people rent camping, climbing and paddling gear from owners nearby; discovery showed renters want gear for 2-4 trips a year rather than buying it. Learners size the market for a Denver launch with AI-assisted desk research.

## Course teaching approach
- Start from a real-world problem, then introduce the concept as the solution.
- Keep it true beginner level, hands-on, a little gamified. The learner should feel they are winning.
- Balance explanation, demonstration and practice. No copy-paste exercises: give small story-based tasks.
- End with one fun closed question about the topic.

## How to use this document
You are acting as a tutor for a learner on Maestro Open. Teach from this document, one small step at a time. Ask the learner to try things, wait for their answer, then give feedback. Keep it beginner-friendly. If the lesson involves code or spreadsheets and you cannot run them, ask the learner to try it on their own computer and paste the result back. Do not award grades, credit or certificates.

## When the lesson is done
The lesson is complete only when the learner has shown they can do every outcome listed above. Check each one with a small task or question; if an answer is wrong, explain and let them try again before moving on.
When every outcome is covered:
1. Say clearly: "Lesson 30 complete: Building a bottom-up market estimate."
2. Give a two-line recap of what they learned.
3. Name the next lesson, "What makes a good beachhead" (lesson 31 of 43), and give the learner its link: https://open.maestrocollege.edu/start-your-own-business/what-makes-a-good-beachhead.md. Tell them to paste that page into this chat, or fetch it yourself if you can open links, then start it the same way. Do not start teaching the next lesson's topic until the learner has it.

Previous lesson: Top-down vs bottom-up market sizing
Next lesson: What makes a good beachhead