Serviceable obtainable market: how to estimate SOM honestly

Guide · Market Growth · 6 min read · last verified 2026-07-24

What is SOM, and how do you estimate it honestly?

Serviceable obtainable market (SOM) is the realistic slice of your serviceable addressable market that you can actually win within a defined window — usually one to three years — given your team, your go-to-market motion, the competition, and the clock. You estimate it bottom-up: real pricing multiplied by a realistic customer count, modelled across conservative, base, and aggressive scenarios. SOM is the one number in the [TAM/SAM/SOM](what-is-total-addressable-market) stack that founders inflate most, because it is the only one a spreadsheet cannot rescue — it is a claim about what you will do, not what exists.

If TAM is the ocean and [SAM](what-is-sam-and-som) is the part of it your product can legally sail, SOM is the catch you can plausibly land this season with the boat and crew you actually have.

SAM to SOM: from reachable to winnable

SOM narrows SAM twice: first to who you can reach, then to who you can win. SAM already excludes the parts of the market your product does not serve. SOM further subtracts the buyers you will not convert in your window — because a competitor owns them, because your sales capacity cannot touch them yet, or because your motion has not matured enough to close them. The gap between SAM and SOM is not pessimism; it is honesty about ramp time and share.

| Dimension | SAM | SOM |

|---|---|---|

| Question it answers | Who could we serve? | Who will we actually win? |

| Time horizon | Static — today's reachable market | 1–3 years, explicit window |

| Limiting factor | Product fit + reachability | Sales capacity, competition, ramp |

| Built from | Segment counts × ACV | Real pricing × realistic wins |

| Typical size | 30–40% share of TAM | Low single-digit % of SAM |

Never take a percentage of TAM

(Figures in this section are sourced inline — category numbers attributed to the named analysts, and Magrios’s own numbers labelled derived or hypothetical worked examples.)

The cardinal SOM sin is the top-down shortcut: "the market is $20B, we'll capture 1%, so we're a $200M business." That number is worthless because the 1% is unearned — it names a share with no mechanism behind it, and investors have seen the slide a thousand times. A credible SOM runs the other way: start from your real price, estimate how many customers you can realistically sign, and let the revenue fall out as arithmetic. Bottom-up forces every optimistic assumption into the open, where it can be argued with. Top-down hides them all inside a single hand-waved percentage.

Build SOM from real pricing × realistic customer counts

Start with prices you actually charge. As a worked example using Magrios's own numbers: Pro lists at $750/user/mo ($225 intro) — $9,000/yr — and Pro+ at $2,097/user/mo ($420 intro) — $25,164/yr; Enterprise is custom. Blended annual contract value (ACV) then depends on plan mix and team size. Illustratively, a portfolio that is single-user-Pro-heavy early blends to roughly $13K; small mixed teams to about $22K; Pro+ and larger teams to about $34K (the per-seat prices are real; the mix and the customer counts are hypothesis).

Now multiply. In this worked example, signing 300 customers by year two at a $22K blended ACV is a $6.6M ARR line — a number you can defend seat by seat, not a fraction of an ocean.

Model three scenarios, not one

(Figures in this section are sourced inline — category numbers attributed to the named analysts, and Magrios’s own numbers labelled derived or hypothetical worked examples.)

(Every market figure in this section is either Magrios's own derived SAM estimate or a bottom-up projection; category sources are named inline, and all forward-looking customer counts are labelled hypothesis.)

A single SOM number is a guess dressed as a fact — model a band instead. Magrios's own market-sizing work triangulates a SAM of roughly $3–5B today (~30–40% share of a $10–20B TAM; derived), tracking the GEO/AEO category — measured at ~$1.0B in 2025 [IntelMarketResearch], with AEO alone ~$655M [MarketIntelo] — as it compounds at a 34–50% CAGR. Against that ~$4B SAM, here are three worked-example three-year scenarios (customer counts are hypothesis; ARR is arithmetic on the real prices above):

| Scenario | Blended ACV | Year 1 | Year 2 | Year 3 | Y3 % of ~$4B SAM |

|---|---|---|---|---|---|

| Conservative | $13K | 25 · $0.3M | 150 · $2.0M | 400 · $5.2M | 0.13% |

| Base | $22K | 50 · $1.1M | 300 · $6.6M | 900 · $19.9M | 0.50% |

| Aggressive | $34K | 120 · $4.1M | 650 · $21.9M | 2,000 · $67.5M | 1.69% |

The honest read is a ~$5–20M ARR three-year SOM, with genuine upside to ~$65M if product-led growth and an upmarket motion both fire and [ACV](what-is-annual-recurring-revenue) expands (hypothesis). Notice that even the aggressive scenario captures under 2% of SAM — that is what a plausible ceiling looks like, not a round-up to 10%.

The honesty check: where founders lie to themselves

SOM is where founders lie to themselves, and the lies are predictable. Watch for these four:

• Unearned share. "We'll take a 10% share of SAM" with no channel, headcount, or win-rate to produce it. Real three-year SOM share is usually low single digits.
• Instant ramp. Booking year-three customer counts in year one. New motions ramp; conversion and referrals compound slowly. Model the S-curve, not a step function.
• Aspirational ACV. Pricing the model at your future enterprise ACV before you have earned a single upmarket logo. ACV should match what you charge today, then expand as evidence accrues — which is why Magrios's early years track the conservative, single-user-Pro-heavy column.
• Pipeline as revenue. Counting every interested account as a win. SOM is closed-won ARR, not the top of the funnel.

Sanity-check your SOM before you present it

(Illustrative checklist — run every SOM through four questions.) Is the year-three share of SAM in the low single digits, and if it is not, what mechanism justifies more? Is the customer count physically reachable given your planned sales and marketing capacity? Does the ACV match your real price list, not a hoped-for one? And does the ramp respect how long deals actually take to close and renew? A SOM that survives all four is fundable; one that fails any is a story you are telling yourself. This is the same discipline behind [the honest market-sizing playbook](the-honest-market-sizing-playbook) and behind [how pricing shapes market size](how-pricing-shapes-market-size) — your SOM is only ever as real as the prices underneath it.

Where SOM sits — and why the small number is the right one

(Figures in this section are sourced inline — category numbers attributed to the named analysts, and Magrios’s own numbers labelled derived or hypothetical worked examples.)

A conservative SOM is not a weak story. A $5M ARR three-year plan on a category compounding at 34–50% toward $10–20B+ is a credible early-stage narrative; the base case (~$20M) is a strong one. What raises money is not the SOM in isolation — it is the share of a compounding category the SOM represents at the moment the category inflects. The move is to name a narrow, winnable entry — a [beachhead market](what-is-a-beachhead-market) you can dominate — and let the SOM grow with your capacity, rather than back-solving customer counts from an ARR target you picked first. Magrios sizes its own market exactly this way: bottom-up, from public evidence and a transparent price list, in a category new enough that even the analysts disagree.