US Airport Carry-On Rules: TSA, PreCheck & Airline Limits

Flying in the United States means navigating two separate systems: TSA security screening rules and individual airline carry-on policies. US security rules are administered by the Transportation Security Administration (TSA) and apply at virtually every commercial airport in the country. Understanding both layers helps you pack correctly, choose the right security lane, and avoid fees at the gate.

TSA Security: Standard Lane Rules

The 3-1-1 Liquid Rule

The TSA applies the 3-1-1 rule to liquids in carry-on bags:

• 3.4 oz (100ml) or less per container
• 1 quart-sized clear zip-top bag
• 1 bag per passenger

Remove the liquids bag from your carry-on and place it in the bin before the X-ray scanner. Gels, creams, pastes, and aerosols all fall under this rule. Exempt from 3-1-1: medications (including liquid medication in any quantity, with a label), baby formula and breast milk, and juice for infants.

What to Remove in Standard Lanes

In standard TSA lanes without PreCheck:

• Shoes off — all footwear must be removed and placed in a bin
• Laptop out — must be removed from the bag and placed flat in a bin
• Liquids bag out — the 1-quart zip bag goes in a separate bin
• Belt and heavy jacket off — metal items and thick outerwear

This process takes time. Budget extra minutes at large airports, especially JFK, LAX, O'Hare, and Hartsfield-Jackson Atlanta, where queues can be long during peak hours.

TSA PreCheck: What You Get

TSA PreCheck is a paid program (approximately $85 for 5 years) that grants access to dedicated security lanes at over 200 US airports. In PreCheck lanes:

• Shoes stay on
• Laptop stays in the bag
• Liquids stay in the bag
• Belt stays on
• Light jacket stays on

PreCheck does not guarantee a shorter queue, but the reduced steps make throughput faster in PreCheck lanes than in standard lanes, even when volume is comparable. PreCheck is worth it for anyone who flies more than two or three times a year domestically.

Enrolling in TSA PreCheck

Apply online at the TSA website, complete an in-person appointment at an enrollment center (located at most major airports and many shipping stores), and provide fingerprints. Approval typically arrives within 3–5 days. Your Known Traveler Number (KTN) goes into your airline profile and appears on boarding passes.

CLEAR: Identity Verification, Not Screening Bypass

CLEAR is a private biometric identity program available at over 50 major US airports. CLEAR uses fingerprint or iris scans to verify your identity at the identity verification step — the document check before the physical screening.

Key distinctions:

• CLEAR skips the ID line only — you still go through full TSA physical screening (shoes off, laptop out in standard lanes)
• CLEAR + PreCheck is the fastest combination: CLEAR bypasses the document queue, PreCheck bypasses the physical screening steps
• Cost is approximately $189/year; Delta SkyMiles and United MileagePlus members receive discounts

Airport-Specific Tips

JFK (New York)

JFK has multiple terminals operated by different airlines with separate security checkpoints. Terminal 4 handles Delta international, Emirates, and several others. Terminal 8 is American Airlines. PreCheck is available at all JFK terminals but queue lengths vary significantly by terminal and time of day.

LAX (Los Angeles)

LAX is undergoing significant terminal renovations through 2026. Security queues at LAX can be long during morning departures (6–9am) and evening returns (4–8pm). The automated screening lanes at Terminals 4 and 5 are faster — look for signage directing you to AUTOMATED lanes.

ATL (Hartsfield-Jackson Atlanta)

ATL is the world's busiest airport. Delta operates from Concourses A through F and the Maynard H. Jackson International Terminal. Security at the main checkpoint (before the underground train) is the primary bottleneck — the PreCheck lanes here move substantially faster than standard lanes during peak travel periods.

O'Hare (Chicago)

O'Hare Terminal 1 serves United; Terminals 2 and 3 serve American and other carriers. PreCheck lanes are available in all terminals. Security at Terminal 3 during morning peaks (6–9am) can be particularly congested.

US Airline Carry-On Size Limits

US domestic carriers have no published weight limit on carry-on bags. Size limits are published but enforcement is inconsistent — most US carriers rely on the overhead bin fitting requirement rather than measuring bags at the gate.

Southwest's dimensions are meaningfully more generous than the three legacy carriers. Southwest also includes 2 checked bags free, which changes the packing calculus for many travelers.

Basic Economy and Carry-On Exclusions

All three legacy carriers offer Basic Economy fares that exclude overhead bin carry-on access:

• American Airlines Basic Economy: personal item under seat only; carry-on charged at the gate
• Delta Basic Economy: personal item under seat only on most domestic routes
• United Basic Economy: personal item under seat only; carry-on charged at the gate at a premium rate

Southwest does not have Basic Economy restrictions — all fares include 2 checked bags and carry-on.

Prohibited Items in US Carry-On Bags

Common items not allowed in carry-on:

• Firearms (may be checked in declared locked containers)
• Knives with blades over 4 inches
• Flammable liquids and gases
• Self-defense sprays (pepper spray) over 4 oz
• Spare lithium batteries over 100 Wh must be in carry-on (not checked)

The TSA prohibited items list is available at tsa.gov and is searchable by item.

Practical Tips for US Airport Security

Sign up for PreCheck before your first trip. The time savings on domestic flights are consistent and the enrollment process is straightforward. Expedited enrollment at many major airports takes under 10 minutes.

Pack a separate quart bag for liquids and put it on top. The most common security delay is passengers unpacking bags at the tray to find their liquids. A dedicated pouch in the outer pocket eliminates this.

At LAX, ATL, and JFK, arrive at least 2.5 hours before domestic departure during summer. Security queue times at these airports during peak periods can exceed 45 minutes in standard lanes.

Southwest's larger size limit matters. If you're flying Southwest with a wheeled carry-on that doesn't fit the 22 × 14 × 9 inch limit, Southwest's 24 × 16 × 10 inch limit may save you a gate check fee.