Ryanair passengers could be turned away from flight moments before departure if they're not careful

If you fly with budget airlines then you'll know that they are incredibly strict with their hand luggage allowances. But Ryanair also has strict rules in places when it comes to checked-in luggage - with one mistake that could see holidaymakers being denied boarding all together.

Passengers can carry a small personal bag free of charge on any Ryanair flight, but it must fit under the seat in front of you and measure no bigger than 40 x 20 x 25cm, like this £11.99 holdall from Amazon. Travellers can also upgrade to a large 10kg cabin bag up to up to 55 x 50 x 20cm, such as the half-price Prestwick Cabin Bag from luxury suitcase brand Antler, which is now £85.

Or if you are going on a longer trip or are known to over pack, you can also opt to add a checked-in suitcase. Ryanair states that checked-in bags can weigh no more than 10kg or 20kg, depending on the option you've booked, and must be dropped off at the airport check-in desk before security. The 20kg bag should be no larger than 80 x 120 x 120 cm, like this one that's on sale for less than £60 at Amazon.

READ MORE: Expert's £2 Tesco tip to 'rid' washing machine limescale with kitchen staple

READ MORE: Major furniture superstore's Easter sale sees 'stylish' sofa £600 cheaper than Marks and Spencer

According to Ryanair's bag policy, anyone who turns up to the boarding gate with their checked-in bag will have to pay an additional charge. The airline's excess baggage fee is up to £11 per extra kilo of luggage, as Birmingham Live reports.

Rule-breakers who refuse to pay the fee will be refused entry onto the flight. Ryanair's policy reads: "If you have purchased a check-in bag, you must check this in at the bag drop desk at the airport.

"If you bring your check-in