What linear inches means and why airlines use it

Linear inches is the sum of your luggage's length, width, and height added together. Airlines use this single number instead of volume because it is faster to check at the gate and harder to game — you cannot compress a suitcase's longest dimension the way you might compress soft items inside it.

When an airline says "carry-on bags must not exceed 22 linear inches," they mean length plus width plus height cannot total more than 22 inches. A bag measuring 20 inches long, 14 inches wide, and 9 inches tall would be 43 linear inches — too large for most carry-on policies, even though it might fit in the overhead bin.

Different airlines set different limits. Most domestic carriers allow 22 linear inches for carry-on. Some budget airlines go as low as 18 linear inches. Checked bags typically max out at 62 to 80 linear inches depending on the airline, with weight limits separate from size limits.

Key Takeaways

  • Linear inches is length plus width plus height — measure the three longest sides of your bag and add them together.
  • Use a soft measuring tape or a rigid ruler; measure from the outside of the bag, including handles and wheels that stick out.
  • Measure your bag when it is empty and sitting flat on a table, not when it is packed or standing at an angle.
  • Check your airline's specific size limits before you travel, because carry-on and checked bag limits vary widely.
  • If your bag is close to the limit, measure it twice and keep a photo of the measurement in case you need to prove it at the gate.

How to measure length, width, and height correctly

Place your empty suitcase on a flat table or floor with the handle retracted and wheels tucked underneath. You are measuring the bag itself, not the space around it.

Length is the longest dimension — usually the distance from the top of the bag to the bottom. Width is the side-to-side measurement across the front. Height is the measurement from front to back, or the depth of the bag. On a typical rolling suitcase, height is usually the smallest number.

Measure from the outside edge to the outside edge. If your bag has a handle that sticks up, include it in the length measurement. If wheels protrude, include them in the height measurement. Measure the actual bag, not the empty space inside.

Use a soft measuring tape if you have one — it wraps around corners without gaps. If you only have a rigid ruler or yardstick, measure each dimension separately and write down the numbers before you forget them. Measure twice. The difference between 21 and 23 linear inches can mean your bag gets flagged at the gate.

Tools you need and where to find them

A soft measuring tape costs two to five dollars at any drugstore, hardware store, or online. It is the easiest tool because it bends around the bag's corners and gives you a single continuous measurement. Sewing supply stores and fabric shops carry them, as do most supermarkets in the section with sewing notions.

A rigid ruler or yardstick works if you measure each dimension separately. A smartphone measuring app can work in a pinch, but it is less reliable than a physical tape — the camera angle affects accuracy, and you cannot verify the measurement by eye the way you can with a tape.

Do not rely on the manufacturer's stated dimensions. Bags are measured differently by different makers, and a bag labeled "22 inches" might actually measure 23 or 24 when you measure it yourself. Measure the actual bag you own.

What to do if your bag is over the limit

If your carry-on bag exceeds your airline's linear inch limit, you have three options: check it instead, buy a smaller bag, or use a different airline with a higher limit.

Checking a bag costs money on most airlines — usually fifteen to thirty dollars for the first checked bag on a domestic flight, though some airlines include one free checked bag with certain ticket types. If you are traveling with only a carry-on to avoid checked bag fees, going over the limit defeats that purpose.

Buying a new bag is worth it only if you travel often. A carry-on suitcase that meets standard airline limits costs forty to eighty dollars for a basic model. If you travel once a year, checking your current bag is cheaper. If you travel four or more times a year, a properly sized bag pays for itself in avoided fees and gate-check hassles.

Before you buy a new bag, verify the manufacturer's stated dimensions by reading customer reviews. Many reviewers mention whether the bag actually fits airline size requirements, and some include photos of the bag in the overhead bin or at the gate.

Measuring bags with unusual shapes

Backpacks and duffel bags are harder to measure because they do not have flat sides. Measure them the same way: place the bag on a table, flatten it as much as possible without forcing it, and measure the longest points in each direction.

For a backpack, measure from the top of the bag to the bottom (length), side to side across the widest point (width), and front to back at the deepest point (height). The straps do not count unless they stick out beyond the bag's main body when the bag is sitting flat.

Soft-sided luggage compresses slightly, which can work in your favor. If your bag measures 23 linear inches when fully expanded but compresses to 21 inches when you pack it carefully, you might get it through carry-on screening. However, do not count on this — airlines measure bags at their maximum dimensions, and a gate agent can expand your bag to check.

How to keep a record of your measurement

Write down your bag's linear inch total and keep it in your phone or email. Include the date you measured it and the airline you are flying. If you own multiple bags, label each one with its measurement using a permanent marker on a luggage tag.

Take a photo of your bag next to a ruler or measuring tape, showing the measurement clearly. If a gate agent disputes your bag's size, you have visual proof. This is especially useful if you are flying a budget airline with strict carry-on policies.

If you buy a new bag, measure it before your trip, not at the airport. Measuring at home gives you time to return or exchange the bag if it does not meet the airline's requirements.

Frequently Asked Questions

Do I measure the bag with the handle up or down?

Measure with the handle retracted. If the handle does not retract, measure with it in its normal position — the position the bag would be in when you are carrying it or placing it in the overhead bin. The goal is to measure the space the bag actually takes up.

What if my bag has wheels that stick out?

Include the wheels in your height measurement. Measure from the bottom of the wheels to the top of the bag. Wheels add one to two inches to the total, so do not forget them — that difference can push you over the limit.

Can I measure my bag when it is packed?

No. Measure the empty bag. A packed bag may compress or expand depending on what is inside, and airlines measure empty bags at the gate. Measuring a packed bag gives you a false number.

Do different airlines measure the same way?

Yes. All airlines measure length plus width plus height. The limits vary — some allow 22 linear inches, others allow 18 or 45 — but the measurement method is the same across all carriers.

What happens if my bag is one inch over the limit?

The gate agent has discretion. Some agents will let a bag that is slightly over pass through, especially if the cabin is not full. Others will enforce the limit strictly. Do not count on getting away with it — if you are over, check the bag or buy a smaller one before you get to the airport.