When you travel by airplane you usually receive a seat assignment that includes a number and a letter. The number tells you which row you were assigned while the letter indicates your specific seat within the row. Commercial jets place letters on individual seats so that you will not get your row number and your seat number confused. This alphanumeric system makes it easier for you to find your assigned seats than an entirely numeric system.
The numbers start at the front of the plane, so business class and first class will have the lowest numbers, and economy class will have higher numbers. Different airlines and aircrafts will be different sizes, so the number of rows and thus aircraft seats depends on how big the plane is.
Order of Letters
The amount of letters in each seating row depends on the aircraft's width. The farthest seat on the left-hand side of the plane is usually assigned the letter "A," with each subsequent seat receiving the next letter in the alphabet. Narrow planes with just two single-seat rows may have only a seat "A" and a seat "B," while wide jets for transcontinental flights tend to have seat letters ranging from "A" through "K."
Most aircrafts skip the letters "I", "S" and "O" because they closely resemble numbers.
Location of Letters
Check your boarding pass to find your row number and seat letter. When you reach your designated aisle, you can find the order of the seats posted below the overhead bins on either side of the row. While seat letters often progress in descending order from the left-hand side of the plane, you should always check the posted sign to be sure you take the correct seat. Seat numbers are also often listed on the seats themselves to prevent further confusion.
When you book a flight online before check-in you may be shown a seating chart or seat map that allows you to select your preferred row number and seat letter, so you can get the best seat for you! Looking at the seating chart as you book your flight gives you an indication of which airline seats might be the most convenient and comfortable. If you prefer a certain type of airplane seat like a window seat or you want to make sure you’re not sitting in an exit row or a middle seat, you can check that here. You can also see what seats are premium economy and have extra legroom or may be able to recline further and where the lavatories are on the seating configuration on the airline’s website.
Additionally, some websites, like Seatguru, rate the comfort level and amenities of different seats on various aircrafts. Knowing whether the plane you’re flying on is a Boeing 747 or Airbus A380 makes a difference. If you don't see a seating plan online, you can call the airline and ask them to send one to you. You can also ask the flight attendants before take-off if you’re able to switch seats then.
Seat Letter Tips
If you have the chance to choose your seat letter but do not have access to a seating chart, you can still try to choose your preferred seat. Generally, normal aircrafts have ABC and DEF for each side of the aisle. If you want an aisle seat, avoid "A" seats, since those are located next to the window on most airlines. In jets with three-seat wide rows, "C" seats" and "D" seats will usually be located closest to the aisle.
Ask the airline about the number of seats in each row to give you an indication of which seat letter to select for your next air travel.