What linear inches means and why airlines measure it
Linear inches is the sum of your luggage's length, width, and height added together. Airlines use this number to enforce carry-on and checked bag size limits, because a bag that measures 22 + 14 + 9 inches adds up to 45 linear inches total. This single number tells them whether your bag fits in the overhead bin or under the seat, regardless of its actual shape.
The reason airlines care about linear inches instead of just weight is that overhead bins and cargo holds have fixed dimensions. A bag can weigh very little but take up too much space, or weigh a lot but fit fine. Linear inches measure what actually matters: whether your luggage physically fits.
Most airlines allow carry-on bags up to 22 × 14 × 9 inches (45 linear inches total), though some budget carriers go lower. Checked bags typically max out at 62 linear inches. Your airline's website lists its exact limits, and those limits are what you measure against.
Key Takeaways
- Linear inches is length plus width plus height, and you measure the longest point on each side of your bag, even if the bag is soft-sided or rounded.
- You need a measuring tape or ruler; measure each dimension separately, then add all three numbers together to get the total linear inches.
- Measure your bag when it is empty and sitting on a flat surface, because the way you pack it can change its shape.
- Most carry-on limits are 45 linear inches, but check your specific airline's website because some allow 50 or 52 and others allow only 40.
- If your bag is soft-sided, measure it at its widest point, because the bag will expand to that size when packed.
How to measure length, width, and height correctly
Place your empty bag on a flat surface with the handle retracted and wheels tucked in. You are measuring the bag itself, not the handle or wheels sticking out. Use a measuring tape or a ruler, and measure in inches (not centimeters, because airline limits are always given in inches).
Length is the longest side of the bag from top to bottom. Width is the side from left to right. Height is the side from front to back. Measure each one at its widest or longest point. If your bag is soft-sided, it will compress or expand depending on how you pack it, so measure it at the point where it would naturally sit when full—usually slightly puffed out, not vacuum-sealed and not completely limp.
Write down all three numbers. Then add them together. That total is your linear inches. For example: 22 + 14 + 9 = 45 linear inches.
Soft-sided bags and bags with expandable sections
Soft-sided luggage (made of fabric rather than hard plastic) can compress or expand, which makes measurement trickier. Measure it at the point where it would sit when you have packed it normally—not stuffed to bursting, and not completely empty and flat. Most soft bags have a natural "full" shape that you can see even when empty; measure at that point.
If your bag has an expandable section (a zipper that lets you add a few extra inches), measure it in the expanded position. Airlines measure bags as they would arrive at the gate, and you will likely use that expansion if you have it. Some airlines allow the expansion; others do not. Check your airline's policy on whether expandable sections count toward the limit.
What to do if your bag is over the limit
If your bag measures over your airline's limit, you have a few options. The simplest is to check the bag instead of carrying it on, if your ticket allows checked bags. Checked bag limits are usually higher (often 62 linear inches), and you can pack more freely.
If you need to carry the bag on, you can try a smaller bag. Many travelers find that a 22 × 14 × 9 inch roller fits most airlines' carry-on limits and still holds a week's worth of clothes. If you are over by just an inch or two, you might get away with it at the gate—some agents measure loosely, and soft bags compress slightly when placed in the sizer frame—but do not count on it. The safest approach is to stay under the limit.
Measuring bags with unusual shapes
Duffel bags, backpacks, and other non-rectangular luggage need the same treatment: measure the longest point on each dimension. For a duffel, that might mean measuring around the bulge at the widest point. For a backpack, measure from the top of the pack to the bottom, side to side at the widest point, and front to back at the deepest point.
If your bag has straps, pockets, or other protrusions, do not measure those. Measure the bag itself. Wheels and handles do not count either. The goal is to measure the actual luggage volume, not every attachment.
Double-checking your measurement before you travel
Measure your bag at least a few days before your flight, so you have time to adjust if it is over the limit. Measure it empty, because that is the true size of the bag itself. Then pack it the way you normally would and look at it—does it seem to expand beyond the empty measurement? If so, remeasure it packed, because that is what the airline will see.
Take a photo of your measurement (tape measure visible in the frame) if you want proof for the airline, though this is rarely necessary. Most airlines trust your word if you say your bag is under the limit, and they will measure it themselves at check-in or the gate if they doubt you.
Frequently Asked Questions
Do I measure the bag with the handle up or down?
Measure with the handle retracted or folded down. The handle is not part of the bag's dimensions. If your bag has a fixed handle that does not retract, measure around it—do not include the handle itself in your height measurement.
What if my bag is round or oddly shaped?
Measure the longest point on each axis. For a round duffel, measure the length end to end, then the circumference at the widest point (that is your width and height combined, so measure the widest point in two directions and use the larger number for both). The goal is to capture the space the bag actually takes up.
Can I measure in centimeters and convert?
You can, but it is easier to measure in inches from the start, since airline limits are always stated in inches. If you only have a metric tape, 1 inch equals 2.54 centimeters, so divide your centimeter measurement by 2.54 to get inches.
Do wheels and handles count toward linear inches?
No. Measure only the bag itself. Wheels, handles, and pockets do not count. The airline measures the luggage volume, not the total footprint with everything sticking out.
What if the airline measures my bag differently than I did?
Airlines use a standard sizer frame at the gate, and they measure the same way you do—length, width, height, then add them up. If your measurement and theirs differ by an inch or two, it is usually because you measured a soft bag in a slightly different state of compression. If your bag is significantly over the limit, the airline may ask you to check it or remove items. Measure conservatively (at the bag's fullest point) to avoid surprises.