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Here's the thing: SIC codes are outdated, unreliable, and often useless for prospecting.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.
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. Every UK company registering with Companies House must select a SIC code. The codes are hierarchical, starting broad and getting more specific. 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. Simple.
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 instead of 7020.
Problem 2: Outdated categories. The last major update to SIC codes was 2007. An entire category of modern business didn't exist then: SaaS, digital marketing, content agencies, growth hacking, marketing automation.
Problem 3: One code, multiple businesses. Many modern companies do multiple things. A digital agency does design, development, marketing, and strategy. Companies can register multiple SIC codes, but most register one primary code.
Common B2B SIC codes
How to actually find companies by what they do
Option 1: Natural language search. Instead of filtering on SIC codes, describe what you're looking for: "digital marketing agencies in London." Tools that use natural language search read company websites and understand what they do beyond the SIC code.
Option 2: Hybrid approach. Use SIC codes as a starting point (cast a wide net), but then manually verify the companies are actually relevant.
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. When you ask for "digital marketing agencies in London," you get actual digital marketing agencies.
Start your free trial at app.firmbase.co/signup
FAQ
Are SIC codes ever accurate?
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.
Should I completely ignore SIC codes?
No. Use them as a starting filter to narrow your universe. Just don't rely on them as your only classification method.
What's the difference between SIC codes and NACE codes?
NACE is the European equivalent. 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.