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market-sizing

phuryn/pm-skills

Estimate TAM, SAM, and SOM using top-down and bottom-up approaches for market opportunity sizing.

What is market-sizing?

Market-sizing helps you estimate the Total Addressable Market (TAM), Serviceable Addressable Market (SAM), and Serviceable Obtainable Market (SOM) for a product or business opportunity. Use it when evaluating market entry, preparing investor pitches, or validating whether a market is worth pursuing.

Define market boundaries and customer segments
Perform top-down TAM estimation from industry size
Build bottom-up TAM estimates using unit economics
Identify SAM constraints (geography, channels, capabilities)
Project SOM based on competitive position and go-to-market capacity
Surface and validate key assumptions underlying estimates

How to install market-sizing

npx skills add https://github.com/phuryn/pm-skills --skill market-sizing

Claude Code

Cursor

Windsurf

Cline

How to use market-sizing

1.Define the market boundaries (problem space, customer segments, geography)
2.Gather industry data and analyst reports via web search
3.Calculate top-down TAM estimate starting from total industry size
4.Build bottom-up TAM using customer count and unit economics
5.Determine SAM by identifying realistic serviceable portion of TAM
6.Estimate SOM based on competitive position and 1-3 year capacity
7.Project growth trends and identify key market drivers
8.Document assumptions and confidence levels for each estimate

Use cases

Good for

Sizing a new product market opportunity before launch
Estimating addressable market for investor pitch decks
Validating market entry decisions across geographies or segments
Cross-validating market estimates using multiple methodologies
Identifying growth drivers and market expansion opportunities

Who it's for

Product managers evaluating new markets
Founders and entrepreneurs preparing pitches
Strategic planners assessing market opportunities
Business development teams evaluating partnerships
Investors conducting due diligence

market-sizing FAQ

What's the difference between TAM, SAM, and SOM?

TAM (Total Addressable Market) is the entire market opportunity. SAM (Serviceable Addressable Market) is the portion your product can realistically serve given constraints. SOM (Serviceable Obtainable Market) is your realistic market share within 1-3 years based on competitive position and go-to-market capacity.

Should I use top-down or bottom-up estimation?

Use both. Top-down starts from industry size and narrows down; bottom-up builds from unit economics. Cross-validating both approaches strengthens confidence in your estimate and reveals where assumptions diverge.

How do I validate my market size assumptions?

Cite sources for all market data (analyst reports, industry benchmarks). Explicitly label estimates vs. data. Identify the most uncertain assumptions and recommend specific research (customer interviews, surveys, competitive analysis) to sharpen them.

What if my top-down and bottom-up estimates don't match?

Reconcile the difference by examining your assumptions. Differences often reveal gaps in data, pricing assumptions, or customer segment definitions. Use this to refine your estimates and identify what research would close the gap.

How should I handle international markets?

Consider currency, purchasing power parity, and regional market maturity. Size each geography separately if significant differences exist, then aggregate. Flag where data quality or market dynamics vary by region.

Full instructions (SKILL.md)

Source of truth, from phuryn/pm-skills.

name: market-sizing description: "Estimate market size using TAM, SAM, and SOM with top-down and bottom-up approaches. Use when sizing a market opportunity, estimating addressable market, preparing for investor pitches, or evaluating market entry."

Estimate Market Size (TAM, SAM, SOM)

Purpose

Estimate the Total Addressable Market (TAM), Serviceable Addressable Market (SAM), and Serviceable Obtainable Market (SOM) for a product. Includes both top-down and bottom-up estimation approaches, growth projections, and key assumptions to validate.

Instructions

You are a strategic market analyst specializing in market sizing, opportunity assessment, and growth forecasting.

Input

Your task is to estimate the market size for $ARGUMENTS within the specified market constraints (geography, industry vertical, customer type, etc.).

If the user provides market research, industry reports, financial data, or competitor information, read and analyze them directly. Use web search to find current market data, industry reports, and growth projections.

Analysis Steps (Think Step by Step)

Market Definition: Define the market boundaries — what problem space, which customer segments, what geography or constraints apply
Top-Down Estimation: Start from total industry size and narrow to the relevant slice
Bottom-Up Estimation: Build from unit economics (customers × price × frequency) to cross-validate
SAM Scoping: Identify which portion of TAM is realistically serviceable given product capabilities, channels, and constraints
SOM Estimation: Estimate achievable share in the next 1-3 years based on competitive position and go-to-market capacity
Growth Projection: Forecast how TAM, SAM, and SOM may evolve over the next 2-3 years
Assumption Mapping: Surface the key assumptions underlying each estimate

Output Structure

Market Definition

Problem space and customer need
Geographic and segment boundaries
Key constraints or scoping decisions

TAM (Total Addressable Market)

Top-down estimate with sources and reasoning
Bottom-up estimate for cross-validation
Reconciliation of the two approaches
Current TAM value (annual revenue opportunity)

SAM (Serviceable Addressable Market)

Which portion of TAM the product can realistically serve
Constraints: geography, language, channels, product capabilities, pricing tier
SAM as percentage of TAM with reasoning

SOM (Serviceable Obtainable Market)

Realistic share achievable in 1-3 years
Basis: competitive position, go-to-market capacity, current traction
SOM as percentage of SAM with reasoning

Market Summary Table

Metric	Current Estimate	2-3 Year Projection
TAM
SAM
SOM

Growth Drivers & Trends

Key factors that could expand or contract the market
Technology, regulatory, demographic, or behavioral shifts
Emerging segments or adjacent markets

Key Assumptions & Risks

Critical assumptions behind each estimate (numbered)
Confidence level for each (high / medium / low)
How to validate the most uncertain assumptions
What would materially change the estimates

Best Practices

Always provide both top-down and bottom-up estimates to triangulate
Use web search for current industry data, analyst reports, and market benchmarks
Cite sources for market data — avoid unsupported numbers
Be explicit about assumptions; label estimates vs. data
Distinguish between value-based (revenue) and volume-based (users/units) sizing
Consider currency and purchasing power parity for international markets
Flag where estimates have wide confidence intervals
Recommend specific data sources or research to sharpen estimates