NAICS Codes for Government Contracting: How to Pick the Right Ones

NAICS codes are the single most consequential classification decision you’ll make when registering as a federal contractor. They determine which contracts you can bid on, whether the government considers you a “small business,” and whether you qualify for set-asides. Get them wrong and you’ll either miss opportunities you’re perfect for or get knocked out of competition on a technicality. This guide explains how NAICS codes work, how to pick the right ones, and the specific mistakes that cost new contractors months of wasted effort.

Table of contents

• What NAICS codes actually are
• How to look up NAICS codes
• Size standards: the money piece
• Primary vs secondary codes
• Common mistakes and how to avoid them
• Updating your NAICS codes over time
• Real examples across industries
• Key takeaways
• FAQ

What NAICS codes actually are

NAICS stands for North American Industry Classification System. It’s a six-digit code that classifies every business in the U.S., Canada, and Mexico by the type of work it does. The U.S. Census Bureau owns it, but for federal contractors it matters because:

1. Every federal solicitation is assigned one NAICS code.
2. That code determines the SBA size standard that applies.
3. Set-asides (small business, 8(a), WOSB, HUBZone, SDVOSB) are scoped to specific NAICS codes.
4. Your registered NAICS codes tell contracting officers what you can do.

The code is hierarchical: the first two digits are the sector (e.g., 54 is “Professional, Scientific, and Technical Services”), the next digits narrow down the subsector, and the last digits hit the specific industry.

Example: NAICS 541511 is Custom Computer Programming Services. Breaking it down: 54 (Professional services), 541 (Professional, Scientific, and Technical Services), 5415 (Computer Systems Design and Related Services), 54151 (Computer Systems Design Services), 541511 (Custom Computer Programming Services).

How to look up NAICS codes

The official source is the Census Bureau NAICS lookup. You can search by keyword, code, or browse the hierarchy. For contracting purposes, also cross-reference:

• SBA Table of Size Standards — the authoritative document matching each NAICS code to its small business threshold
• SAM.gov entity registration — where your codes actually get recorded for federal contracting
• Your state’s vendor registration — state codes may use NAICS or their own taxonomy

Pro tip: When you’re researching opportunities on RFPHawk or SAM.gov, look at which NAICS code the contracting officer used for similar past contracts. If DoD consistently uses 541330 (Engineering Services) for the work you do, that’s the code to register, even if 541512 (Computer Systems Design) feels closer to your day-to-day.

Size standards: the money piece

The SBA defines “small business” per NAICS code, and the standard is either revenue-based or employee-based:

NAICS Code	Description	Size Standard
541511	Custom Computer Programming	$34M avg revenue
541512	Computer Systems Design	$34M avg revenue
541330	Engineering Services	$25.5M avg revenue
541611	Admin Management Consulting	$27.5M avg revenue
236220	Commercial Building Construction	$45M avg revenue
561612	Security Guards & Patrol	$29M avg revenue
336411	Aircraft Manufacturing	1,500 employees
517311	Wired Telecom Carriers	1,500 employees

“Revenue” here is your three-year average of receipts (five-year for construction and certain others as of recent SBA rule changes — check the current standard). Size is calculated as of the date of your offer, not award.

Why it matters

If a solicitation is set aside for small businesses under NAICS 541511 and your three-year revenue average is $35M, you’re not small for that code and your bid will be rejected even if you’re perfectly qualified technically. Worse, if you misrepresent your size — intentionally or not — you face False Claims Act exposure.

Primary vs secondary codes

In your SAM.gov registration you pick one primary NAICS code and unlimited secondary codes. Rules of thumb:

• Primary should be the code that generates the majority of your commercial revenue. This is also the code the SBA uses for certain eligibility calculations (like 8(a)).
• Secondary codes should be everything you can legitimately do and want to bid on. There’s no cap on the number of secondaries and no real downside to listing more, within reason.

A consulting firm that writes custom software but also does strategic advisory work might have 541511 as primary and 541611, 541618, 541690, 541990 as secondaries.

Don’t list codes you can’t actually perform. Contracting officers check past performance against NAICS, and having dozens of unrelated codes looks like shotgun marketing.

Common mistakes and how to avoid them

Mistake 1: Picking the closest-sounding code instead of the right one

A cybersecurity firm instinctively reaches for 541512 (Computer Systems Design) because it sounds technical. But for cybersecurity services specifically, agencies often use 541519 (Other Computer Related Services) or 541690 (Other Scientific and Technical Consulting). Research what agencies actually use for the work you do.

Mistake 2: Not updating codes when your business evolves

If you added a new service line two years ago and never updated SAM.gov, you’re invisible for those solicitations.

Mistake 3: Overreaching on primary code

Some contractors pick the NAICS code with the highest size standard to stay “small” longer. This is legal but can backfire — if your primary doesn’t match your actual revenue mix, 8(a) eligibility reviews get awkward.

Mistake 4: Missing the “exception” footnotes

The SBA size standards table has footnotes for certain codes, especially in IT and professional services, that change the threshold based on contract type or customer. Read the fine print.

Mistake 5: Ignoring the ancillary codes

There’s a special bucket of NAICS codes (often 56-prefixed and services) that get used for contracts you’d never expect. A janitorial company may also fit 561720 (Janitorial Services) AND 238910 (Site Preparation Contractors) if they do post-construction cleanup.

Updating your NAICS codes over time

You can update SAM.gov registration at any time — there’s no annual review trigger. Most contractors do a full audit:

• Every 12 months, aligned with SAM.gov renewal
• Any time you launch a new service line
• After winning a contract under a NAICS code you hadn’t registered (add it immediately)
• Before applying for a certification like 8(a) or WOSB (the primary code choice matters for eligibility)

Real examples across industries

Managed IT services firm:

• Primary: 541513 (Computer Facilities Management Services)
• Secondaries: 541512, 541519, 518210, 811212

General contractor, commercial:

• Primary: 236220 (Commercial Building Construction)
• Secondaries: 238990, 237310, 561730

Management consulting:

• Primary: 541611 (Administrative Management Consulting)
• Secondaries: 541618, 541990, 611430, 541613

Marketing agency:

• Primary: 541810 (Advertising Agencies)
• Secondaries: 541820, 541830, 541890, 541430

Key takeaways

• NAICS codes determine what you can bid on and whether you’re “small.” Get them right or forfeit opportunities.
• Your primary code should reflect your actual revenue mix; secondaries should cover everything you can legitimately do.
• Research what codes agencies actually use for your type of work — don’t guess.
• Size standards vary wildly ($25M to 1,500 employees). Know yours.
• Audit your registration annually and whenever you add a service line.

Ready to see which opportunities match your NAICS codes? Browse RFPs or sign up for personalized match scoring.

FAQ

Can I bid on an RFP with a NAICS code I haven’t registered in SAM.gov? Technically yes for many contracts, but some solicitations require the code to be on your registration as a condition of bid. Easier path: register every code you realistically do work under.

How many secondary NAICS codes should I have? There’s no magic number, but most established contractors have 10–30. More than 50 starts looking suspicious to contracting officers.

What if my NAICS code has multiple size standards listed (footnotes)? Read the specific solicitation. The contracting officer picks which size standard applies. When in doubt, ask during the Q&A period.

Do state contracts use NAICS codes? Most do, but not universally. Some states have their own commodity codes (like NIGP codes in many jurisdictions). Register for both where required.

What’s the difference between NAICS and PSC codes? NAICS describes industries; PSC (Product Service Codes) describes specific products/services the government buys. Federal solicitations assign both. For discovery, NAICS is the more useful filter day-to-day.