Verdict
On Spirit and Frontier the free allowance is a personal item only — roughly 18 x 14 x 8 inches — and everything bigger costs money. The counterintuitive part is that a carry-on usually costs more than a checked bag: Spirit carry-ons start around $49 versus about $44 for a checked bag, and Frontier runs roughly $45 versus $40. Both airlines cap checked bags at 40 lb rather than the 50 lb the majors allow, which means overweight fees arrive sooner.
Comparing carriers? Compare airline carry-on limits, then measure the whole suitcase before checking your flight requirements.
Key Facts for Fast Answers
Buy nothing until you have measured the free personal item. A soft duffel built to roughly 18 x 14 x 8 inches can hold several days of clothing and costs nothing to fly.
Check fit, price, and product details before buying.
Buy nothing until you have measured the free personal item. A soft duffel built to roughly 18 x 14 x 8 inches can hold several days of clothing and costs nothing to fly.
Full Analysis
On Spirit and Frontier, a carry-on typically costs more than a checked bag. Airlines want bags in the hold to speed up boarding, and they price accordingly. If you are going to pay for space, check the bag.
Free personal item vs paid carry-on
| Airline | Free personal item | Carry-on size | Carry-on fee |
|---|---|---|---|
| Spirit | 18 x 14 x 8 in | 22 x 18 x 10 in | From ~$49 |
| Frontier | 18 x 14 x 8 in (14 x 18 x 8 also listed) | 24 x 16 x 10 in | From ~$45 |
Checked bag fees and limits
| Airline | 1st checked bag | 2nd checked bag | Weight limit |
|---|---|---|---|
| Spirit | From ~$44 | From ~$54 | 40 lb |
| Frontier | From ~$40 | From ~$50 | 40 lb |
Both airlines use 62 linear inches as the checked size limit, same as the majors. The weight limit is where they diverge: 40 lb instead of 50 lb. A bag that flies free of surcharge on Delta can generate an overweight fee on Spirit.
Why the free personal item is the whole game
- Roughly 18 x 14 x 8 inches is smaller than any suitcase sold as a carry-on, so the right tool is a soft bag, not a hardshell spinner.
- Soft sides let you compress into the sizer. A rigid case that measures one inch over fails outright.
- Both airlines check personal item size at the gate on many flights, and gate pricing is the most expensive tier.
- Adding bags during the original booking is consistently cheaper than adding them afterward.
What luggage makes sense for Spirit and Frontier
This is the rare case where we would not point you at a hardshell spinner. A soft duffel or a compressible backpack sized close to 18 x 14 x 8 inches is the piece that flies free. If you already own a standard 22 x 14 x 9 carry-on, it works fine on Delta, United, American, and Southwest — but on Spirit and Frontier it becomes a paid bag, and a checked fare is the cheaper way to bring it.
The Problem
Travelers assume that carrying a bag on is the cheap option, because it is on every other airline. On Spirit and Frontier that assumption is backwards — the overhead bin is the premium product, and the cargo hold is the discount. Booking a fare and then adding a carry-on at the gate is the most expensive way to fly either airline.
Options
Free. Roughly 18 x 14 x 8 in, must fit under the seat. The cheapest way to fly either airline.
From about $44 on Spirit and $40 on Frontier when prepaid. Usually cheaper than a carry-on.
From about $49 on Spirit and $45 on Frontier, and significantly more at the gate.
Both airlines discount bags heavily when added during the original booking rather than later.
Scenario Recommendations
- Buy nothing until you have measured the free personal item. A soft duffel built to roughly 18 x 14 x 8 inches can hold several days of clothing and costs nothing to fly.
- If you need more than a personal item, check the bag instead of carrying it on. The price difference is real and it is the opposite of what you expect.
- Weigh carefully. The 40 lb checked limit is 10 lb below every major carrier, and overweight fees are steep relative to a cheap base fare.
Carry-on size & airline rules
Your next luggage decision
Find the size and weight questions to check before your flight.
Include wheels, handles, pockets and expanded depth.
Go directly to the rules for the airline you are flying.
Match a suitcase to your route and packing needs.
FAQ
What is the free personal item size on Spirit?
About 18 x 14 x 8 inches. It must fit under the seat in front of you. Spirit charges for anything larger, including a standard carry-on.
What is the free personal item size on Frontier?
About 18 x 14 x 8 inches, must fit under the seat. Frontier, like Spirit, charges separately for overhead bin space.
Why does a Spirit carry-on cost more than a checked bag?
Because Spirit prices overhead space at a premium to encourage bags into the cargo hold, which speeds up boarding. Carry-ons start around $49 while checked bags start around $44.
What is the checked bag weight limit on Spirit and Frontier?
40 lb per bag, which is 10 lb less than the 50 lb standard at Delta, United, American, and Southwest. Oversize and overweight fees apply on top.
Can I bring a normal 22x14x9 carry-on on Spirit?
Yes, but it counts as a paid carry-on, not a personal item. Expect roughly $49 or more, and considerably more if you pay at the gate.
Is it cheaper to add bags when booking or later?
When booking. Both airlines price bags substantially higher when they are added after the reservation, and highest at the airport or gate.
Do Spirit and Frontier charge for carry-on on every fare?
They charge for overhead carry-on space on their standard fares. Higher bundles and elite tiers may include a carry-on, so check the specific fare you are buying.
What luggage should I buy for Spirit or Frontier?
A soft duffel or compressible backpack close to 18 x 14 x 8 inches. A hardshell spinner cannot compress to fit the free personal item sizer.
Final Recommendation
On Spirit and Frontier the free allowance is a personal item only — roughly 18 x 14 x 8 inches — and everything bigger costs money. The counterintuitive part is that a carry-on usually costs more than a checked bag: Spirit carry-ons start around $49 versus about $44 for a checked bag, and Frontier runs roughly $45 versus $40. Both airlines cap checked bags at 40 lb rather than the 50 lb the majors allow, which means overweight fees arrive sooner.
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