Intro.
#The Precise Definitions of TAM, SAM, and SOM
The three market-size figures are concentric circles zooming into the same market. TAM is the outermost ring, SAM sits inside it, and SOM is the smallest circle at the center. Show only one of the three, and a VC will immediately question the other two.
| Term | Definition | What It Really Means |
|---|
| TAM (Total Addressable Market) | The entire market if your product captured 100% share worldwide | A theoretical ceiling |
| SAM (Serviceable Available Market) | The market you can actually reach within geographic, language, regulatory, and channel constraints | Your realistic territory |
| SOM (Serviceable Obtainable Market) | The market you can realistically capture within the next 3-5 years (typically 5-15% of SAM) | Where your actual revenue comes from |
VCs don't get excited about TAM. It's just a minimum bar — 'is this game big enough to play' — while the real investment decision happens at the SAM and SOM level.
02
#Top-Down Estimation: Fast but Weak on Evidence
Top-down estimation starts with a huge number from an external report and works down by multiplying it by your segment's share. You can produce a slide in 30 minutes this way, but if the ratios you multiply at each step aren't well-supported, the number balloons.
- Example: a ₩30T domestic ad market x 60% digital share x 80% mobile share = ₩14.4T
- Pro: fast, and sourcing looks clean when it cites government statistics or market research reports
- Con: hard to verify whether the multiplied ratios actually correspond to your specific business
- VC reaction: they immediately ask, 'Of that ₩14.4T, how much can you actually sell?'
주의
A pitch deck with only a top-down estimate defaults to looking like an inflated SAM. Standard practice is to also calculate it bottom-up and show both numbers side by side.
03
#Bottom-Up Estimation: The Method VCs Trust More
Bottom-up estimation builds the number up using the formula 'price per customer x number of customers = market.' Because it starts from your actual price list and a real count of potential customers, the number may look smaller — but VCs trust it far more.
| Variable | Value | Basis |
|---|
| Price per customer | ₩50K/month SaaS | Current company price list |
| Potential customers | 700,000 SMEs nationwide | Government business census |
| 3-year penetration rate | 1% | Comparable SaaS market penetration curve |
| Annual market (SOM) | ~₩4.2B | ₩50K x 12 x 7,000 customers |
The real value of bottom-up isn't the number itself — it's that it breaks your business model down into variables. When price per customer, customer count, and penetration rate are all clear, a VC immediately understands which lever grows the market.
04
#Cross-Checking Both Estimates: A Facebook Ads Market Example
When top-down and bottom-up converge on similar values, your slide gets much stronger. Say an adtech startup sells a Facebook ads solution — running both methods looks like this.
- Top-down: global digital ad market of roughly ₩700T x Facebook's ~25% share = TAM of ₩175T
- Bottom-up: number of advertisers running Facebook ads x average solution price x solution penetration rate = SAM
- If both numbers land in the same order of magnitude, the slide passes — if they're off by an order of magnitude, one of them is wrong
Wherever the two methods diverge is exactly where your assumptions are weakest. If top-down comes out much larger, you're missing a segment that falls outside your SAM; if bottom-up is much smaller, you've under-defined your price point or use case.
TIP
What VCs love most on a market slide is a single line that reads: 'top-down: ₩X trillion, bottom-up: ₩Y trillion, and the two estimates converge.' The act of cross-checking itself proves your analytical rigor.
05
#"This Market Looks Too Small": What the Rejection Really Means
When a VC says 'this market looks too small,' what they really mean is: 'this SOM can't return 10x within our fund's 8-year term.' The fund's own structure forces that answer.
| Fund Variable | Value | Implication |
|---|
| Fund term | ~8 years | Must exit within this window |
| Target return | 10x per deal (3-5x for the fund overall) | A handful of portfolio companies need to hit 10x+ to pull up the average |
| Deals reviewed per year | ~100 | Only 2-3 of these result in an investment |
| #1 disqualifying factor | A SOM that can't return 10x within 8 years | If the market's too small, even 100% share falls short |
So being told the market is 'small' doesn't mean your business model is bad. It's a quantitative rejection: 'even under this SOM x market-share scenario, the numbers don't fit our fund's return model.' The right response isn't to defend the business model — it's to make a stronger case for how SOM grows over time.
주의
The real reason angels and VCs look at 100 deals a year and fund only 2-3 is that a SOM capable of hitting 10x within the fund's term is genuinely rare. The market slide is the tool that gets you past this calculation.
06
#Four Common Mistakes on Market Slides
The four mistakes an investor catches most often within the first 30 seconds of opening a pitch deck follow a set pattern.
- Showing only TAM with no SAM or SOM — a single line like 'a global ₩1,000T market' gets the deck cut on the spot
- Calling it SAM when it's actually global TAM multiplied by a country's share — this ignores geographic, language, and regulatory constraints
- SOM exceeding 50% of SAM — straying outside the recommended 5-15% range raises doubts about realism
- Market size not matching the business model — citing B2C ad-market figures when the actual product is B2B SaaS
The fourth mistake is the most damaging. When Korean grocery-delivery pioneer Market Kurly mapped out the dawn-delivery market, the key wasn't 'the entire food market' — it was 'the number of households that could realistically subscribe to premium fresh groceries.' Their market slide passed because they isolated that exact segment.
07
#The Four Elements of a Market Slide VCs Trust
A market slide that passes contains all four of the following elements. If they don't fit on one slide, splitting it into two is fine.
| Element | Expected Standard | Example |
|---|
| Sourced quantitative data | Government statistics, market research firms, public company filings | National statistics office, industry regulator, public filings |
| Both top-down and bottom-up estimates | Both figures converge to the same order of magnitude | Top-down: ₩14T / Bottom-up: ₩11T |
| SOM 3-5 years out | Calculated using CAGR plus your company's penetration rate | Currently ₩4.2B -> ₩30B in 3 years |
| One trend driving SAM growth | Regulatory easing, new-tech adoption, demographic shifts, etc. | Expanding mandatory e-invoicing requirements |
체크
When these four elements line up on one slide, VCs mentally check off 'market slide: passed' and move on to the next one — team, traction. Simply not getting stuck on the market slide is itself major progress.
Summary.
#Six Self-Checks Before You Hit Send
Before sending your pitch deck, run the market slide through these six checks one last time to avoid the number-one reason decks get cut.
- Do TAM, SAM, and SOM all appear on one slide?
- Did you calculate SAM using both top-down and bottom-up methods?
- Is the data source cited in the body text or a footnote?
- Is SOM within 1-15% of SAM?
- Does the market size match your business model (B2C/B2B/B2G)?
- Does this SOM x your projected 5-year market share satisfy a VC fund's IRR target (10x)?
CTA
If you get stuck on question six, it's not that your market is small — your SOM scenario is weak. Upload your business plan or pitch deck to OpenSeed, and we'll diagnose your market slide's estimation method, sourcing, and SOM ratio against the same criteria VCs use to cut decks, flagging inflated numbers and missing calculation steps along the way.
Get Your Market Slide Diagnosed Against VC Cut Criteria
OpenSeed's AI review checks in one pass whether your TAM/SAM/SOM figures are cross-validated top-down and bottom-up, whether your SOM ratio falls within a realistic range, and whether your market size matches your business model. Upload your business plan or pitch deck and we'll flag the weakest link in your market-sizing slide first.
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