What Linear Inches Means and Why Airlines Use It

Linear inches is the sum of your luggage's length, width, and height added together in a single number. Airlines use this measurement instead of volume because it's quick to check at the gate and prevents bags from being too long or too wide to fit in overhead bins or cargo holds, even if they're not heavy.

A bag measuring 22 inches long, 14 inches wide, and 9 inches tall would be 22 + 14 + 9 = 45 linear inches. Most domestic airlines allow carry-on bags up to 45 linear inches; checked bags often have a 62 to 80 linear inch limit depending on the airline. The measurement itself is straightforward, but the way you measure matters—measure the outside of the bag, not the inside, and include any pockets or handles that stick out.

Key Takeaways

  • Linear inches is length plus width plus height; add all three dimensions together to get one number.
  • Measure the outside of your bag from the furthest points, including any protruding pockets, handles, or wheels.
  • Most carry-on limits are 45 linear inches; checked bag limits range from 62 to 80 linear inches depending on your airline.
  • A soft-sided bag can compress slightly at the gate, but a hard-sided bag cannot, so measure hard luggage at its widest point.

Gather a Measuring Tape and Measure Each Dimension

Use a soft measuring tape (the kind tailors use) or a flexible ruler—a rigid ruler or yardstick makes it harder to follow the contours of your bag. If you only have a rigid ruler, you can use a piece of string, mark the length on the string, then measure the string against a ruler.

Place your bag on a flat surface and measure from the bottom to the top for height. Measure from the left side to the right side for width. Measure from the front to the back for length. Always measure the outside of the bag, including any exterior pockets, wheels, or handles that extend outward. If your bag has wheels that fold in, measure with the wheels in their normal position—the position they'll be in when you travel.

Write down all three numbers. If your bag is soft-sided and compressible, measure it in the state it will be when you pack it—not completely empty and not overstuffed. Hard-sided luggage should be measured at its widest point, which is usually when the lid is closed normally.

Add the Three Measurements Together

Once you have length, width, and height, add them together. If your bag is 24 inches long, 16 inches wide, and 10 inches tall, the math is 24 + 16 + 10 = 50 linear inches.

Write this total down and keep it with your luggage information. If you travel with the same bag regularly, you won't need to measure again—the linear inch total doesn't change unless you buy a different bag.

Check Your Airline's Specific Size Limits

Different airlines set different limits. Most major U.S. carriers allow carry-on bags up to 45 linear inches, but some budget airlines like Spirit and Frontier allow only 40 linear inches for carry-on. Checked bag limits typically range from 62 to 80 linear inches, with most airlines at 62 or 70.

Look up your specific airline on their website before you travel. The size policy is usually under "baggage" or "what can I bring." Some airlines also charge extra fees if your bag exceeds the limit by even a few inches, so knowing your bag's measurement ahead of time prevents surprises at the airport.

Common Mistakes When Measuring

The most common error is measuring the inside of the bag instead of the outside. Airlines care about how much space your bag takes up in the plane, not how much you can fit inside it. Measure the exterior dimensions only.

Another mistake is ignoring wheels, handles, or pockets that stick out. If your rolling bag has wheels that add 2 inches to its depth, that 2 inches counts toward your linear total. Similarly, if a pocket bulges out when packed, measure at that bulge point, not at the flat part of the bag.

A third error is measuring a soft bag when it's completely empty and compressed. Soft luggage will expand slightly when packed, so measure it in a realistic packed state—not bursting, but not flat either. Hard-sided bags don't compress, so measure them however they naturally sit.

What to Do If Your Bag Is Over the Limit

If your bag exceeds your airline's carry-on limit, you can check it instead (if it's under the checked bag limit). If it exceeds both limits, you have a few options: buy a smaller bag, remove items and pack them in a personal item like a backpack, or pay the oversized baggage fee if your airline charges one.

Some airlines charge $50 to $100 per flight for bags over the limit, so it's worth measuring before you get to the airport. If you're close to the limit—within 2 or 3 inches—a soft-sided bag may compress enough to fit, but a hard-sided bag will not.

Frequently Asked Questions

Do I measure the bag with or without the handle extended?

Measure with the handle in the position it will be during travel. If your rolling bag's handle extends upward when you're pulling it, that height counts. If the handle retracts completely, measure without it extended. Most people travel with the handle up, so measure that way.

What if my bag is soft-sided and I can compress it more at the gate?

Soft bags can compress slightly, but airlines measure at the gate in their normal packed state, not when squeezed. Measure your bag as you would normally pack and carry it. If it's slightly over the limit, compression might help, but don't count on it—pack as if your measurement is your limit.

Do wheels count toward the linear inches?

Yes. Wheels are part of your bag's exterior, so measure from the furthest point the wheels extend. If your bag is 22 inches long but the wheels add 1 inch, measure 23 inches for length.

Can I measure my bag in centimeters instead of inches?

Airlines always publish limits in inches for U.S. travel. Measure in inches to match their stated limits. If you measure in centimeters, divide by 2.54 to convert to inches. A 56-centimeter bag is about 22 inches.

What if my bag is an unusual shape, like a duffel or backpack?

Measure the longest point for length, the widest point for width, and the tallest point for height, even if those points aren't on the same side of the bag. For a duffel, measure end to end for length, around the widest bulge for width, and top to bottom for height. Add those three numbers together the same way.