SIC codes explained
By Anna Fontanes | March 2026 | 8 min read
If you've ever used a list-building tool, you've probably filtered by "industry" and seen SIC codes as options. SIC code 6202. SIC code 7320. They're cryptic numbers that supposedly categorise what companies do.
Here's the thing: SIC codes are outdated, unreliable, and often useless for prospecting. But they're everywhere because they're the official UK classification system, so companies are required to register with one.
Understanding what they are - and why they're not fit for purpose - is important for anyone prospecting UK companies.
What SIC codes are
SIC stands for Standard Industrial Classification. They're a UK government system for categorising companies by what they do.
Every UK company registering with Companies House must select a SIC code (or multiple codes). The codes are hierarchical, starting broad and getting more specific:
- Section level: One letter (e.g., "M" for professional, scientific, and technical activities)
- Division level: Two numbers (e.g., "62" for computer programming)
- Group level: Three numbers (e.g., "620" for computer programming)
- Class level: Four numbers (e.g., "6202" for computer consultancy)
Most companies register with a 4-digit class code.
Why they're theoretically useful
The idea is sound: assign companies to a category, then sellers can filter for all companies in that category.
Looking for software companies? Filter for SIC code 6202 (computer consultancy) or 6201 (computer programming) or 6203 (computer facilities management). Get a list of all companies with those codes.
Simple. Efficient. Logical.
In practice, it breaks down immediately.
Why SIC codes are unreliable
Problem 1: Self-selection and misclassification
When a company registers with Companies House, they choose their SIC code. They're not audited on this choice. A management consulting firm that does some development work might register under SIC 6201 (software development) instead of 7020 (management consulting). A SaaS company that started as a consultancy might keep its original SIC code.
Self-selection means misclassification is endemic.
Problem 2: Outdated categories
The last major update to SIC codes was 2007. That's 17 years ago. An entire category of modern business didn't exist then: SaaS, subscription software, digital marketing, content agencies, growth hacking, marketing automation, data analytics, cloud infrastructure.
A company doing "digital marketing" doesn't have a perfect SIC code. Are they "advertising" (7311)? "Software development" (6201)? "Business consultancy" (7020)? Depends on the company's interpretation.
Problem 3: One code, multiple businesses
Many modern companies do multiple things. A digital agency does design, development, marketing, and strategy. A SaaS company does software development and service. A management consultancy does strategy and implementation.
Companies can register multiple SIC codes, but most register one primary code. That one code can't capture the full picture of what they do.
Problem 4: Subsidiaries and complex structures
A company might be a subsidiary of a larger group. Its SIC code might describe the subsidiary's function (e.g., "employee leasing company") rather than what the group actually does (e.g., software development). If you're looking for "software companies" by SIC code, you might miss a subsidiary that's part of a software group.
The practical impact: false positives and false negatives
These problems create two outcomes:
False positives: You filter for "software companies" by SIC code 6201 and get a list that includes a management consulting firm that does some development work. Half your list is noise.
False negatives: You filter for "software companies" and miss a pure-play SaaS company that registered under "business consultancy" because they grew from a consulting background.
This is why filtering by SIC codes returns lists with tons of irrelevant companies that technically match the code but aren't actually relevant.
Common B2B SIC codes (and what they actually mean)
Here's a reference guide for the most common B2B SIC codes. Remember: the category is official, but company fit within the category is unreliable:
| SIC Code | Official Description | What it usually means | What it sometimes means |
|---|---|---|---|
| 6201 | Computer programming | Software companies, developers | Consulting firms that code, in-house dev teams |
| 6202 | Computer consultancy | Software consultants, IT consultants | SaaS companies, any tech service company |
| 6203 | Computer facilities management | Managed IT services, IT support | Data centres, cloud infrastructure |
| 6209 | Other IT service activities | IT staff leasing, IT support, IT training | Catch-all for anything IT that doesn't fit above |
| 7020 | Business management consultancy | Management consultants, strategy consultants | Can include tech consultants, change management |
| 7120 | Engineering design | Engineering consultancies, design firms | Product design, UX design, any design-adjacent work |
| 7310 | Advertising | Advertising agencies | Full-service agencies, some digital agencies |
| 7320 | Market research | Market research companies | Can include some consultancy and data analysis |
| 6110 | Wired telecommunications | ISPs, telecoms providers | Broadband, internet service providers |
| 6130 | Other telecommunications | Mobile networks, satellite services | Less relevant for B2B sales |
| 4711 | Supermarkets | Retail | Irrelevant for most B2B |
How to actually find companies by what they do
If SIC codes are unreliable, how do you find companies in your target market?
Option 1: Natural language search
Instead of filtering on SIC codes, describe what you're looking for: "digital marketing agencies in London" or "software development companies in the Midlands."
Tools that use natural language search read company websites and understand what they do beyond the SIC code. They categorise companies by what they actually do, not by what they registered as.
Option 2: Hybrid approach
Use SIC codes as a starting point (cast a wide net), but then manually verify the companies are actually relevant by reading their websites or LinkedIn profiles.
That's more work, but it's more accurate than trusting SIC codes alone.
Option 3: Custom data enrichment
If you're looking for very specific company types, you can enrich your list with additional data (website analysis, LinkedIn data, job postings) to identify the companies that actually fit your criteria rather than relying on SIC codes.
Why we mention this
You'll encounter SIC codes wherever you're doing UK B2B prospecting. List-building tools use them as a filtering option. Companies House data includes them. It's worth understanding that they're a starting point at best, not a reliable classification system.
If you see a list-building tool positioning itself as having "accurate SIC code filtering," be sceptical. That's a marketing claim masking an inherently unreliable system.
Firmbase doesn't rely on SIC codes for categorisation
Instead, we analyse what companies actually do based on their websites, job postings, and filing data. That means when you ask for "digital marketing agencies in London," you get actual digital marketing agencies, not a mix of advertising, consulting, and design firms registered under vague SIC codes.
Start your free trial to search by what companies actually do, not by bureaucratic codes.
FAQ
Q: Are SIC codes ever accurate?
A: They're accurate at the broadest level. If a company is registered under SIC 6201, they definitely do something technology-related. But that's as granular as you can rely on them. For any specific use case, they're too broad.
Q: Can I improve my list by combining SIC codes?
A: Yes. If you filter for multiple SIC codes (6201, 6202, 6203, 7020), you get broader coverage but also more noise. Still doesn't solve the fundamental problem of self-selection and misclassification.
Q: Do larger companies have more accurate SIC codes?
A: Slightly. Larger companies are more likely to be reviewed or audited, so misclassification is less common. But it's still endemic.
Q: How do I check what SIC code a company is registered under?
A: Go to Companies House and search for the company. Their SIC code is listed on their profile.
Q: Should I completely ignore SIC codes?
A: No. Use them as a starting filter to narrow your universe. Just don't rely on them as your only classification method.
Q: What's the difference between SIC codes and NACE codes?
A: NACE is the European equivalent. UK companies sometimes register with NACE codes as well. They're roughly equivalent to SIC codes and have the same limitations.
Author Bio
Anna Fontanes is a revenue operations consultant who has built account scoring and ICP frameworks for UK B2B sales teams across SaaS and professional services. She specialises in making structured prospecting work for teams without dedicated ops resource.
