When flying with low-cost airlines, the dimensions of your hand luggage often require close attention. After all, exceeding a given airline's limits could result in having to pay to check the bag in. Having recently examined the different allowances of Europe's budget giants, let's now turn our attention to the US.

Allegiant Air

Starting alphabetically, Allegiant Air is rather restrictive regarding what passengers can bring onboard for free. Indeed, they are only entitled to a single bag, with dimensions no larger than 17.8 cm x 38.1 cm x 40.6 cm.

Such cabin baggage has to be stored under the seat in front of you, with the overhead bins reserved for larger bags, (dimensions up to 22.9 cm x 35.6 cm x 55.9 cm). As is becoming common at budget operators around the world, passengers must pay a fee to bring such luggage with them, ranging from $10 to $75.

Stay informed: Sign up for our daily and weekly aviation news digests.

Frontier Airlines

Frontier Airlines operates on a similar basis when it comes to hand luggage, with passengers only entitled to a small free bag measuring up to 35.6 cm x 45.7 cm x 20.3 cm. Once again, this has to be placed underneath a seat.

For a fee, Frontier's passengers can bring larger hand luggage to be placed in the overhead bins. Such bags have a weight limit of 35 lbs (15.9 kg), and their dimensions must be no larger than 25.4 cm x 40.6 cm x 61 cm. The exact fees vary, but, using a Boston-Miami flight next week as an example, this would start at $60.

Southwest Airlines

Southwest Airlines is known for its generous checked baggage policy, which allows all passengers to bring two hold bags with them for free. As it happens, its hand luggage policy is also kinder than its fellow US budget carriers.

Indeed, as long as they fit the prescribed dimensions, passengers are allowed to bring an under-seat bag and one to be stored in the overhead bins. The maximum permitted dimensions for these bags are 41.3 cm x 34.3 cm x 20.3 cm (28.8 liters) and 61 cm x 40.6 cm x 25.4 cm (62.9 liters) respectively.

The airline industry is always full of new developments! What aviation news will you check out next?

Spirit Airlines

Over at Spirit Airlines, passengers are, once again, only entitled to a single piece of free cabin baggage. With maximum dimensions of 45 cm x 35 cm x 20 cm (including handles and wheels), these are best placed under a seat.

Spirit allows passengers to bring larger carry-on bags (56 cm x 46 cm x 25 cm) with them for a fee, with the rates depending on the exact flight. Using our Boston-Miami example, this would start at $38 for a flight next week. Active military personnel are exempt from such fees, and can also bring two checked bags for free.

Sun Country Airlines

Fifth and finally, Sun Country Airlines allows passengers to bring a single piece of free hand luggage onboard, with its measurements not exceeding 43.2 cm x 33 cm x 22.9 cm. Overhead bags are limited to 35 lbs (15.9 kg) in weight, with maximum dimensions of 61 cm x 40.6 cm x 27.9 cm. Adding this to a Boston-Minneapolis flight next week would cost passengers between $30 and $50 (time-dependent).

What do you make of the hand luggage allowances at major US budget carriers? How many have you flown with? Let us know your thoughts and experiences in the comments!