As of 13 August 2026, AI can estimate your UK market size.

What to actually do

1. Hand it to a person

   The route this page recommends

   A person who owns the outcome does this end to end, worth it when the failure is dear.

2. Use a tool built for this

   Second choice

3. Do it yourself

   The distant third

   A chat interface, chat-fluent skill, and roughly 1 hour until you can act on the result.

   How to actually do it

   1. Write down your offer, paying customer, UK geography, price, buying frequency, delivery capacity and route to market in a single working document.
   2. Gather your own evidence, including sales, enquiries, survey responses, waitlist records and customer counts, and label each item with its date and source.
   3. Open GOV.UK, relevant UK industry sources and company reports, then collect only market definitions, population counts, business counts, spending figures or other evidence that directly relates to your target customer.
   4. Paste the business details, evidence and source links into the prompt, and ask the chatbot to calculate TAM, SAM and SOM with both methods where possible.
   5. Paste the returned formulas and inputs into a spreadsheet, recalculate each result independently, and compare the units, customer definition, geography and price assumptions with your original notes.
   6. Open every material source link, replace weak or outdated inputs with better evidence where available, then record a conservative, central and optimistic estimate before using the result in your business plan.

   Prompt

   Estimate the UK market size for my business using the information below. Produce a transparent TAM, SAM and SOM estimate, using both a top-down approach and a bottom-up approach where the data allows it. Define each market clearly before calculating it. Show every formula, input, unit and assumption. Separate sourced facts from my assumptions and your inferences. Use current UK sources where available, give the source name and URL for each material fact, and state when a source is unavailable or too weak to support a precise estimate. Do not invent figures, customer counts, growth rates or competitor data. Use ranges rather than false precision. Identify double counting, missing segments, geographic limits, price assumptions and likely sources of bias. Finish with a short table of the inputs I should verify and a list of the additional data that would most improve the estimate.
   
   Business description: [what the business sells]
   Target customer: [who pays and who uses it]
   UK geography: [areas served or planned]
   Price and buying frequency: [price, contract length or purchase frequency]
   Current evidence: [sales, enquiries, survey results, waitlist, customer numbers or other evidence]
   Capacity and route to market: [how many customers you could serve and how you would reach them]
   Known competitors or substitutes: [names or categories]
   Relevant sources or files: [URLs, spreadsheets or documents]

   Open it prefilled in ChatGPT or Claude, or copy it into Gemini, which takes no prefill link.