Market Sizing 101

Market Sizing 101: How Big Is Your Opportunity?

Before you pour your energy into a business idea, you need to answer one crucial question: Is the market big enough to be worth it?

Market sizing is the process of estimating how many potential customers exist and how much money they could spend on your product. It sounds complicated, but the basic framework is surprisingly simple — and it is one of the most powerful tools in any entrepreneur's toolkit.

Why Market Size Matters

Imagine you have invented the world's best left-handed fountain pen case. It is beautifully designed, perfectly functional, and priced fairly. But how many left-handed fountain pen users are there in your area? Maybe 12. That is not a business — that is a very expensive hobby.

Market sizing helps you:

• Avoid dead-end ideas before you waste time and money
• Compare opportunities — which of your ideas has the biggest potential?
• Set realistic goals — knowing your market helps you predict revenue
• Impress backers — crowdfunding supporters want to know your idea has real potential
• Plan for growth — understand where your limits are and where the opportunities lie

The Three Circles: TAM, SAM, SOM

Market sizing uses three concentric circles, each getting smaller and more realistic.

#### TAM — Total Addressable Market

The entire pie. This is everyone in the world who could theoretically buy your type of product.

Example: If you are selling revision cards, your TAM is every secondary school student in the UK — roughly 5.5 million students.

TAM is deliberately huge. It represents the total opportunity if you had unlimited resources and zero competition. Nobody actually captures their full TAM.

#### SAM — Serviceable Addressable Market

The slice you could realistically reach. This narrows TAM down to the people you could actually serve given your location, distribution method, and resources.

Example: You can only sell revision cards to students in your city and online. Your city has 15 secondary schools with about 12,000 students, plus you estimate 3,000 students might find you online. SAM = 15,000 students.

#### SOM — Serviceable Obtainable Market

The slice you will actually get. This is the realistic number of customers you can win in your first year, accounting for competition, awareness, and your limited starting resources.

Example: In year one, you will sell mainly at your own school (800 students), two nearby schools through friends (1,200 students total), and maybe 200 online orders. Realistically, you might convert 10% of those people. SOM = 220 customers.

Visualising the Three Circles

Think of it like a dartboard:

`

┌─────────────────────────────────────────┐

│ TAM: 5.5 million │

│ (All UK secondary students) │

│ │

│ ┌────────────────────────┐ │

│ │ SAM: 15,000 │ │

│ │ (Your city + online) │ │

│ │ │ │

│ │ ┌──────────┐ │ │

│ │ │SOM: 220 │ │ │

│ │ │(Year one)│ │ │

│ │ └──────────┘ │ │

│ └────────────────────────┘ │

└─────────────────────────────────────────┘

`

How to Calculate Each Level

#### Calculating TAM: Top-Down Approach

For TAM, you work from big numbers down. Government statistics, industry reports, and simple Google searches are your friends.

Step 1: Define what category your product falls into.

Step 2: Find the total number of potential customers in the UK (or your country).

Step 3: Estimate how much each customer might spend per year on this category.

Step 4: Multiply: TAM = Number of customers x Average spend per year.

Example: Homemade Candles

• UK adults who buy candles: approximately 18 million (according to industry data)
• Average spend on candles per year: roughly £30
• TAM = 18 million x £30 = £540 million

That does not mean you will make £540 million. It means the total candle market in the UK is that size.

Where to find numbers:

• Office for National Statistics (ons.gov.uk) — population data, household spending
• Statista — industry statistics (some free data available)
• GOV.UK — education statistics, regional data
• Google: "how many [customers] in UK" usually gets you started

#### Calculating SAM: Narrow It Down

For SAM, apply realistic filters:

• Geography: Where can you actually deliver or sell?
• Demographics: Which segment of the TAM matches your ideal customer?
• Distribution: Can you reach them through the channels you plan to use?
• Price point: Who can actually afford your specific product?

Example: Homemade Candles (continued)

• You sell at local markets and online within the UK
• Your candles are premium, eco-friendly, priced at £8-12
• Your target is eco-conscious adults aged 20-45 in your county
• Your county has about 500,000 adults, roughly 25% are eco-conscious in that age range
• SAM = 125,000 people x £20 average spend on premium candles = £2.5 million

#### Calculating SOM: Get Real

SOM is where you need to be brutally honest with yourself. Consider:

• How many people will actually hear about you? (Your reach in year one is small)
• What is a realistic conversion rate? (Of people who hear about you, how many will buy?)
• How much competition is there? (What share can you realistically win?)
• What are your production limits? (Can you actually make enough product?)

Example: Homemade Candles (continued)

• Year one: you sell at 12 local markets (reaching ~3,000 people) and drive ~1,000 online visitors
• Conversion rate at markets: 15% (good for a well-presented stall)
• Online conversion: 3% (typical for a new small brand)
• Market sales: 3,000 x 15% = 450 candles
• Online sales: 1,000 x 3% = 30 candles
• Total: 480 candles at average £10 each
• SOM = £4,800 in year one revenue

See how different that is from the £540 million TAM? That is why SOM matters most for planning.

Real UK Teen Business Examples

Let us size three common teen businesses:

#### Example 1: School Bake Sale Business

#### Example 2: Social Media Management for Local Businesses

#### Example 3: Custom Phone Case Shop (Online)

Bottom-Up vs. Top-Down: Two Approaches

There are two ways to estimate market size. Good entrepreneurs use both and see if the numbers roughly agree.

#### Top-Down (Start Big, Filter Down)

Start with the total population and narrow it down using filters. This is what we have been doing above.

Pros: Quick, uses published data.

Cons: Can be wildly optimistic if your filters are too generous.

#### Bottom-Up (Start Small, Build Up)

Start with what you can actually sell and scale up from there.

Step 1: How many units can you personally produce/deliver per week?

Step 2: How many weeks per year will you sell?

Step 3: What is your price per unit?

Step 4: Multiply them together.

Example: Handmade Jewellery

• You can make 20 pieces per week
• You sell for 40 weeks of the year (accounting for holidays and exam time)
• Average price: £7
• Bottom-up SOM = 20 x 40 x £7 = £5,600/year

Pros: Very realistic, based on your actual capacity.

Cons: Might underestimate potential if you could scale up.

Pro tip: If your top-down SOM and bottom-up SOM are in the same ballpark, you can be fairly confident in your estimate.

Sanity Checks: Is Your Number Realistic?

After calculating your market size, run these sanity checks:

• The "sniff test" — Does the number feel reasonable, or did you accidentally assume everyone in your city would buy from you?
• The competition check — If competitors exist, are they all making the kind of money your numbers suggest?
• The capacity check — Can you physically produce and deliver enough product to hit your SOM?
• The time check — Do you have enough hours alongside school to run this business?
• The "so what?" test — Is your SOM big enough to be worth your effort? If your realistic year-one revenue is £200, is that worth the investment?

When the Market Is Too Small

Sometimes your market sizing reveals an uncomfortable truth: the market is just too small. This is actually valuable information — better to find out now than after you have spent months building the product.

If your market is too small, you have three options:

• Expand your geography — Could you sell online nationally instead of just locally?
• Broaden your product — Could you serve a wider customer base with a slightly different product?
• Pivot completely — Take what you have learned and apply it to a bigger opportunity.

When the Market Is Huge (But You Are Small)

A massive TAM can be exciting but also misleading. If the candle market is worth £540 million, it does not mean there is room for you. Ask:

• How many established competitors are there?
• Do they have advantages you cannot match (factories, brand recognition, retail deals)?
• Is there a specific niche within the big market that is underserved?

Often the best strategy is to find a niche within a big market — a small, specific segment that big companies are ignoring. For example, instead of "candles," target "soy candles with funny labels for teenage gift-giving." Much smaller market, but much less competition.

Key Numbers to Remember

Here are some useful UK statistics for teen entrepreneurs:

• UK population: ~67 million
• Secondary school students: ~5.5 million
• Average teen pocket money: £7-10 per week
• Percentage of teens with a smartphone: ~95%
• Number of UK secondary schools: ~3,500
• UK small businesses: ~5.5 million
• Average household spends ~£580/week total

These numbers can serve as starting points for your TAM calculations.