A SIC code (Standard Industrial Classification code) is a five-digit number that describes a UK company's main business activity. Every limited company registered at Companies House must declare at least one SIC code, making it the standard way to classify companies by industry. There are over 700 individual codes on the Companies House condensed list, organised into 21 broad sectors covering everything from agriculture and construction to IT services and hospitality.
If you've only encountered SIC codes when registering your own company, you might think of them as a box-ticking exercise. But for accountants, insurance brokers, business development teams, and anyone who works with large numbers of companies, SIC codes are one of the most useful filtering tools available. They let you cut through the noise of thousands of company records and focus only on the industries you care about.
How the SIC code system is structured
The current system is called SIC 2007, last updated by the Office for National Statistics to align with European and international classification frameworks. Despite the name, it's still the version in use today. The structure works as a hierarchy, moving from broad to specific:
Sections are the top level, labelled A through U. Each section covers a broad area of the economy. Section F is construction. Section G is wholesale and retail. Section J is information and communication. There are 21 sections in total.
Divisions sit within sections and use two-digit numbers. For example, Division 41 (within Section F) covers "Construction of buildings", while Division 43 covers "Specialised construction activities". There are 88 divisions.
Groups add a third digit for more specificity. Group 43.2, for instance, covers "Electrical, plumbing and other construction installation activities". There are 272 groups.
Classes use four digits. Class 43.21 is "Electrical installation", while 43.22 is "Plumbing, heat and air-conditioning installation". There are 615 classes.
Subclasses are the most specific level, using all five digits. This is what you see on the Companies House register. Code 43210 is "Electrical installation" and 43220 is "Plumbing, heat and air-conditioning installation". There are 191 subclasses, though many classes don't subdivide further - in those cases the five-digit code simply adds a zero to the four-digit class.
In practice, most people work with the five-digit codes directly and don't think much about the hierarchy. But understanding the structure is useful when you want to target a broad sector (all of construction, for example) rather than a single activity within it.
The 21 SIC code sections
Here's what each top-level section covers, along with its letter code and the division numbers it contains:
A - Agriculture, Forestry and Fishing (01-03). Farming, forestry, and commercial fishing. Includes growing crops, raising animals, and logging.
B - Mining and Quarrying (05-09). Extraction of minerals, oil, gas, and stone.
C - Manufacturing (10-33). Everything from food processing and textiles to electronics and vehicle manufacturing. One of the largest sections by number of codes.
D - Electricity, Gas, Steam and Air Conditioning Supply (35). Energy generation and distribution.
E - Water Supply, Sewerage, Waste Management (36-39). Water treatment, waste collection, and recycling.
F - Construction (41-43). Building construction, civil engineering, and specialist trades like electrical and plumbing. Consistently the single largest sector for new UK company formations, accounting for nearly 16% of all businesses on the register.
G - Wholesale and Retail Trade (45-47). Includes vehicle sales, wholesale distribution, and all forms of retail from high-street shops to online stores.
H - Transportation and Storage (49-53). Road haulage, rail, shipping, air transport, warehousing, and postal services.
I - Accommodation and Food Service (55-56). Hotels, restaurants, pubs, cafes, and catering.
J - Information and Communication (58-63). Publishing, broadcasting, telecoms, software development, IT consultancy, and data processing. A rapidly growing section for new company formations.
K - Financial and Insurance Activities (64-66). Banking, insurance, pension funds, and financial services. Includes holding companies (64200), one of the most commonly used individual codes.
L - Real Estate Activities (68). Buying, selling, renting, and managing property.
M - Professional, Scientific and Technical Activities (69-75). Legal and accounting services, management consultancy, architecture, engineering, advertising, and scientific research. The second-largest section for new formations after construction.
N - Administrative and Support Service Activities (77-82). Recruitment, security, cleaning, office support, and travel agencies.
O - Public Administration and Defence (84). Government and public services. Rarely relevant for private sector company searches.
P - Education (85). Schools, universities, driving instruction, and training providers.
Q - Human Health and Social Work (86-88). Hospitals, GP practices, dental surgeries, care homes, and social work.
R - Arts, Entertainment and Recreation (90-93). Theatres, museums, sports facilities, gambling, and amusement parks.
S - Other Service Activities (94-96). Membership organisations, repair services, hairdressers, and personal services.
T - Activities of Households (97-98). Households as employers of domestic staff.
U - Activities of Extraterritorial Organisations (99). International bodies like embassies and the UN. Also includes codes 99999 (dormant companies with no significant activity) and 74990 (non-trading companies), which are worth knowing because they appear frequently on the register.
How to find a company's SIC code
Every company's SIC code is publicly visible on the Companies House register. Search for any company at find-and-update.company-information.service.gov.uk, scroll to the "Nature of business (SIC)" section, and you'll see one to four five-digit codes with their descriptions.
If you want to browse the full list of available codes, Companies House publishes a condensed SIC code list at resources.companieshouse.gov.uk/sic/. This is the definitive list - Companies House uses a condensed version of the full ONS classification, and only codes on this list are accepted in filings. Using a code from the full ONS list that doesn't appear on the Companies House condensed list will result in a rejected filing.
What SIC codes can't tell you
SIC codes are useful but imperfect. A few things worth knowing:
Companies often choose vague codes. There's no penalty for picking a broad or slightly inaccurate SIC code, so many companies default to generic options like 82990 ("Other business support service activities not elsewhere classified") or 70229 ("Management consultancy activities other than financial management"). This means SIC codes are better for broad industry filtering than for precise activity matching.
Codes don't update automatically. A company can only change its SIC code by filing a Confirmation Statement. If a business pivots from retail to software development, its SIC code might still say "retail" until the next annual filing. For newer companies this is rarely an issue, but for older ones the code may be out of date.
The system is from 2007. SIC 2007 predates many modern business categories. There's no specific code for "SaaS company" or "influencer marketing agency" or "electric vehicle charging network". These businesses end up spread across codes like 62020 (Information technology consultancy), 73110 (Advertising agencies), or 45200 (Maintenance and repair of motor vehicles) - none of which are a perfect fit. The system captures the broad sector well enough, but the specific code descriptions don't always reflect what a company actually does in practice.
Dormant companies use catch-all codes. Code 99999 ("Dormant company, no significant accounting transactions") and 74990 ("Non-trading company") appear frequently. If you're using SIC codes to find active businesses, you'll want to filter these out - they're not prospects for anyone.
How professionals use SIC codes in practice
For most business professionals, SIC codes aren't something you think about when filing your own company's paperwork. They're a tool for finding and filtering other people's companies. Here's how different industries use them:
Accountants use SIC codes to identify new companies in sectors they specialise in. If your practice focuses on construction, you can filter the stream of new company formations to show only Section F codes, which cuts out roughly 84% of the noise and leaves you with the companies most likely to need your specific expertise.
Insurance brokers use SIC codes to target industries with specific insurance requirements. A company coded under 43210 (Electrical installation) needs very different cover to one coded under 62020 (IT consultancy). SIC codes let brokers focus their prospecting on sectors where they have competitive products.
Business development teams use SIC codes to segment the market. If you sell HR software, you probably care most about companies in sections that employ large workforces - construction, manufacturing, hospitality, healthcare. SIC codes let you filter for those sectors without reading thousands of company descriptions.
Compliance and due diligence teams use SIC codes to flag high-risk sectors. Certain industries have higher regulatory scrutiny or fraud risk. Monitoring new formations in specific SIC codes can be part of a broader risk management process.
Tools like Slopless let you apply SIC code filters to a real-time feed of new company formations, so you only see companies in your target industries the moment they register. You can save filter presets for different sectors and switch between them, or combine SIC code filters with geographic filtering to narrow results further - for example, showing only new construction companies forming in the North West.
The most common SIC codes on the register
Certain SIC codes appear far more frequently than others. Knowing which ones dominate can help you understand the landscape and set realistic expectations about the volume of companies you'll see in each sector.
The codes that consistently appear most often on new company formations include:
68209 - Other letting and operating of own or leased real estate. Property companies, buy-to-let SPVs, and real estate holding structures. Extremely common because every property investor who sets up a limited company for a rental property uses this code.
41100 - Development of building projects. Property developers and construction project companies.
62020 - Information technology consultancy activities. The default code for a wide range of tech companies, from genuine IT consultancies to freelance developers and software startups.
70229 - Management consultancy activities (other than financial management). A very broad catch-all that covers everything from genuine management consultancies to sole-trader consultants in almost any field.
47910 - Retail sale via mail order houses or via internet. All e-commerce businesses, from large online retailers to individuals selling on Etsy or Amazon.
96090 - Other personal service activities not elsewhere classified. A catch-all for services that don't fit neatly into other codes - personal trainers, life coaches, pet sitters, and more.
64200 - Activities of holding companies. Any company set up primarily to hold shares in other companies.
If you're filtering new company formations by SIC code, these high-volume codes will produce the largest result sets. More specific codes (like 43210 for electrical installation or 86230 for dental practice activities) will produce smaller but more targeted lists.
Using SIC codes to find the right companies
The most effective way to use SIC codes is not to search for individual codes one at a time but to build a set of codes that covers your target market comprehensively. If you're an accountant targeting the construction sector, that's not just 41100 (development of building projects) - it's also 41201 (construction of commercial buildings), 41202 (construction of domestic buildings), 42110 (construction of roads and motorways), 43210 (electrical installation), 43220 (plumbing), 43290 (other construction installation), 43310 (plastering), 43320 (joinery), 43341 (painting), 43390 (other building completion), and several more.
Building these code sets manually from the condensed list is time-consuming but worth doing once. Once you have your list, you can apply it as a filter to any data source - whether that's a lead list, an API query, or a real-time monitoring tool. The filter stays the same; only the data source changes.
Combining SIC code filtering with other signals makes it even more effective. A new construction company on its own is mildly interesting. A new construction company whose director already runs three other active construction companies is a serious prospect. And a new construction company that's also just launched a website is a company that's clearly open for business.
Slopless lets you filter the real-time stream of new UK company formations by any combination of SIC codes. Build custom filter presets for your target industries, combine with geographic filtering by postcode area, and see only the companies that matter to you. Log in or get in touch to get started.