What Are Linear Inches and How to Calculate Them
Linear inches (or linear dimensions) is a measurement commonly used by airlines and shipping companies to determine size restrictions for luggage, packages, and cargo. It represents the sum of the three dimensions of an object: length, width, and height.
The Linear Inches Formula
Calculating linear inches is straightforward:
For example, a suitcase measuring 30 × 18 × 14 inches has:
Linear Inches = 30 + 18 + 14 = 62 linear inches
How to Measure Your Luggage Correctly
To get accurate measurements, follow these steps:
- Use a tape measure or ruler - A flexible tape measure works best for luggage with curved edges.
- Measure the longest point of each dimension - Include any bulging or protruding parts.
- Include external features - Wheels, handles, pockets, and any attachments count toward total size.
- Measure when packed - A full suitcase may bulge more than an empty one.
- Round up to the nearest inch - Airlines don't give partial-inch credit.
Pro Tip: Measure When Packed
Soft-sided luggage and duffel bags can expand significantly when full. Always measure your bag when it's packed to the level you'll actually travel with to avoid surprises at the airport.
Why Airlines Use Linear Inches
Airlines adopted linear dimensions as a sizing standard because:
- Simplicity - One number to check instead of three separate dimensions
- Flexibility - Allows for different shape configurations that still fit in cargo holds
- Universal standard - Easy to communicate and verify at check-in
- Cargo optimization - Helps airlines maximize luggage loading efficiency
Common Airline Size Restrictions
Carry-On Luggage
Most airlines allow carry-on bags with maximum dimensions around:
- Linear limit: 45 inches (114 cm)
- Typical dimensions: 22 × 14 × 9 inches (56 × 36 × 23 cm)
- Must fit: Overhead bin or under the seat in front of you
Checked Baggage
Standard checked bag limits across major airlines:
- Linear limit: 62 inches (158 cm)
- Weight limit: Usually 50 lbs (23 kg) for economy class
- Common dimensions: 30 × 18 × 14 inches or similar combinations
Oversized Baggage
Bags exceeding 62 linear inches typically incur additional fees:
- 63-80 linear inches: Oversize fee applies ($100-200 typically)
- Over 80 linear inches: May require freight shipping
- Sports equipment: Often has special rules and fees
Important: Always Check Your Airline
Size limits vary by airline, route, and ticket class. Budget carriers often have stricter limits, while premium tickets may include larger allowances. Always verify current policies on your airline's website before traveling.
Linear Inches for Shipping Packages
Shipping companies like UPS, FedEx, and USPS also use linear inches (often called "girth" or "dimensional weight") to calculate shipping costs:
- UPS: Packages over 130" combined length and girth may require special handling
- FedEx: Maximum 165" for most services (length + girth)
- USPS: Combined length and girth cannot exceed 130" for Priority Mail
Converting Between Inches and Centimeters
If you're traveling internationally or have metric measurements:
Linear cm = Linear inches × 2.54
Linear inches = Linear cm ÷ 2.54
For example, 62 linear inches equals approximately 157.5 cm (62 × 2.54).
Tips for Staying Within Size Limits
- Choose the right luggage: Look for bags specifically designed to meet airline limits
- Compression packing: Use packing cubes or compression bags to reduce bulging
- Avoid overpacking: Leave room for souvenirs or unexpected items
- Consider bag weight: Some bags are designed to be lightweight while maximizing space
- Check measurements regularly: Bags can stretch or deform over time
What Happens If Your Bag Is Too Large?
If your luggage exceeds the linear inch limit at check-in:
- Checked bags: Oversize fees range from $75 to $200+ depending on airline
- Carry-on bags: May be gate-checked (often free) or require checked bag fees
- Extreme cases: Bag may be refused entirely or require cargo shipping
Using this calculator before you travel helps you avoid these costly surprises and ensures a smoother airport experience.