Linear inches is simply length plus width plus height added together as a single number. Airlines use it because it lets one figure govern bags of very different shapes: a long thin case and a short fat one can both be accepted or both be refused on the same rule. Delta, for example, states that baggage size must not exceed 62 inches when you total length plus width plus height, and most major carriers use the same threshold for a standard checked bag.
This calculator from Arb Digital adds the three dimensions, converts between inches and centimetres, and compares the total against the allowance you select. Arb Digital publishes it in a free tools library that covers a lot of measurement and logistics arithmetic; this page is the specific case of a passenger bag against an airline threshold.
What This Linear Inches Calculator Does
Enter three dimensions in whichever unit your tape measure uses. The tool reports the linear total in both inches and centimetres, the amount of headroom you have against the selected allowance, the bag's internal capacity in litres, and a separate pass or fail against a typical 45-inch carry-on limit. The pass or fail language appears in the headline panel so you do not have to compare two numbers yourself.
Boundaries with the closest tools on the site. The length converter and cm to inches convert a single measurement and have no summing or limit-checking behaviour. The volume converter moves between litres, gallons and cubic feet but does not derive volume from dimensions. The freight class calculator and pallet calculator deal with commercial shipments rather than passenger baggage. This page is the linear-sum rule specifically.
How to Use It
- Pack the bag first. Measure it in the condition it will actually be presented in, not flat and empty.
- Measure the widest points. Run the tape over wheels, feet, handles and side pockets rather than around them.
- Pick your unit and enter all three sides. Order does not matter — addition is commutative, so which side you call length is irrelevant.
- Select the allowance that matches your ticket, or enter a custom figure taken from your carrier's own baggage page.
- Read the headroom. Anything under about two inches of clearance is worth double-checking, since measurement at the counter is rarely gentle.
The Formula / How It's Calculated
The linear total is simply L + W + H. Unit conversion uses the exact international relationship: NIST confirms on its SI Units – Length page that the inch, derived from the 1959 yard definition, is exactly equivalent to 25.4 mm. So linear centimetres are linear inches multiplied by 2.54, and the reverse divides by the same factor. Capacity is L × W × H, converted from cubic inches to litres by multiplying by 0.016387064.
Worked example, matching the defaults. A case measuring 27 × 21 × 14 inches totals 62 linear inches, exactly on the standard checked-bag threshold. Converted, that is 68.58 + 53.34 + 35.56 = 157.48 cm. Its volume is 27 × 21 × 14 = 7,938 cubic inches, which is 7,938 × 0.016387064 = 130.1 litres. Against a 45-inch carry-on limit it is 17 inches over, so it fails that check comfortably.
The 62 In / 157 Cm Rounding Gap
Notice something in the worked example: 62 inches converts to 157.48 cm, but airlines publish the metric limit as 157 cm. The two published figures are not the same threshold. A bag that is exactly 157.48 cm passes an inch-based check and fails a strict centimetre-based one by half a centimetre.
In practice this almost never matters, because half a centimetre is well inside measurement error and staff are not measuring to that precision. But it explains a real source of confusion when a bag is described as "62 inches / 157 cm" and someone converts one figure and finds it does not match the other. The rounding is deliberate on the airline's part — 157 is the tidier number — and the inch figure is the original. If you are near the line, work in the unit the carrier's published limit is written in.
The same rounding appears at every tier. 45 inches is 114.3 cm but is usually published as 114 cm; 80 inches is 203.2 cm published as 203. Each time, the metric figure is very slightly the tighter one. For pure conversions where the exact value matters, the length converter keeps the full precision rather than the marketing rounding.
What Airlines Actually Measure, and What They Do Not
Two things catch travellers out repeatedly. The first is that wheels and handles count. A case advertised as 22 inches tall is often 23 or 24 inches over the wheels and the handle housing, and the sizer at the gate does not care what the label said. Manufacturers frequently quote the body dimension only. Measure your own bag rather than trusting the marketing figure.
The second is that expansion zips count when they are open. A case that clears the limit closed can exceed it by two inches expanded, which is exactly when you are most likely to have used the expansion — on the way home. If you expect to expand it, calculate the expanded figure and travel to that number.
What airlines generally do not do is apply the linear rule to a bag that is already inside a hard sizer at the gate. Carry-on limits are usually enforced by fitting the box rather than by adding three numbers, which is a stricter test in one respect: a bag can meet 45 linear inches while being too deep to fit. Always check the individual side limits for cabin bags, not just the total.
Why Linear Inches and Capacity Are Not the Same Thing
Two bags with identical linear totals can hold very different amounts, because the sum is linear and the volume is a product. A 21 × 21 × 20 inch case totals 62 linear inches and holds 8,820 cubic inches. A 40 × 12 × 10 case also totals 62 linear inches but holds only 4,800 — barely more than half as much, for the same allowance.
The general rule is that a cube maximises volume for a fixed linear sum, so the closer a bag is to cubic, the more you get for your allowance. That is why so many checked cases converge on similar proportions. It also means that when you are choosing luggage, comparing quoted litres is a better guide to what you can pack than comparing the linear figure, which only tells you whether the bag is permitted. The volume converter handles the conversions if a manufacturer quotes cubic feet or gallons instead.
Weight Limits Are a Separate Test
Size and weight are enforced independently, and a bag can pass one while failing the other. A 62-inch case is easily large enough to exceed a typical 23 kg or 50 lb allowance long before it is full, particularly if it is a hard-shell design that weighs five or six kilograms empty. Overweight fees are frequently charged in addition to oversize fees, not instead of them.
The practical implication for anything dense — books, tools, sample stock — is that weight will bind first and the size calculation is irrelevant. For anything bulky and light, size binds first. Work out which of the two constraints you are actually near before optimising the wrong one. If you are moving goods rather than personal effects, the freight class calculator uses density rather than either limit alone, and the container loading calculator covers packing efficiency for larger consignments.
Arb Digital's free tools library covers dimensional, volumetric and unit-conversion calculations for travel and shipping, and our team is happy to talk through anything the tools cannot answer.
Browse Free Tools Talk to Arb DigitalCommon Mistakes to Avoid
- Measuring the empty bag — soft cases gain size when packed, and that is the size that gets checked.
- Excluding wheels and handles — the published product dimension often omits them, but the counter measurement does not.
- Measuring closed then travelling expanded — an expansion zip can add two inches to the linear total.
- Assuming carry-on is only a linear rule — cabin bags are usually tested against individual side limits and a physical sizer.
- Ignoring the weight allowance — size and weight are separate tests, and fees for exceeding them are usually cumulative.
Related Free Tools From Arb Digital
Use the length converter for exact unit conversions, cm to inches for a single quick figure, the volume converter for capacity in other units, the feet and inches calculator when a measurement is written in mixed units, and the freight class calculator when the shipment is commercial rather than personal. Everything else is in the free online tools hub.
Frequently Asked Questions
Length plus width plus height added together into one figure. A case measuring 27 by 21 by 14 inches is 62 linear inches. Which side you call length makes no difference, because the three numbers are simply summed.
Most major carriers use 62 linear inches, published in metric as 157 cm. Always confirm on your own carrier's baggage page, because low-cost and regional airlines sometimes set a smaller figure and route-specific rules exist.
Yes. Airlines measure the bag at its widest points including wheels, feet and the handle housing. Manufacturers often quote the body dimension only, which is why a bag can measure larger than its advertised size.
Because the inch is exactly 25.4 mm, so 62 inches is 157.48 cm precisely. Airlines round the published metric figure down to 157, which makes the metric limit fractionally tighter than the imperial one.
Yes, and by a large margin. Linear inches is a sum while volume is a product, so a near-cubic case can hold almost twice as much as a long narrow one with the identical linear total.
No. Size and weight are enforced separately, and checked-bag fees depend on your fare and route regardless of size. Meeting the linear limit only means the bag will not attract an oversize charge.
Check each side against the individual limits rather than relying on the linear total, because cabin bags are usually tested by fitting a physical sizer. The 45-inch figure in this tool is a common total, not a substitute for the per-side rules.
