Duffle bag capacity is measured in litres, and while the numbers seem straightforward, what each size actually holds in practice can be confusing. Is 40L enough for a week-long trip? Will 25L fit your gym gear? This guide translates abstract litre measurements into practical terms, helping you choose a size that matches your actual needs.
Understanding Litre Measurements
Capacity ratings indicate the total internal volume of the bag in litres. However, this doesn't account for the bag's shape, compartment divisions, or how efficiently you pack. A 40L duffle and a 40L backpack hold the same theoretical volume, but the duffle's open design often accommodates awkwardly shaped items better.
Keep in mind that manufacturer measurements aren't standardised. Two "40L" bags from different brands may have noticeably different actual capacities. When in doubt, check user reviews or detailed dimensions.
As a rough guide, each 10L of capacity holds approximately one day's worth of casual clothing for most people. So a 40L bag comfortably fits 3-4 days of clothes plus toiletries and accessories.
Size Categories Explained
Extra Small (Under 20L)
These compact bags serve as personal items or minimal gym bags. They're not true travel duffles but serve specific purposes.
What it holds:
- A change of clothes
- Basic toiletries
- Water bottle
- Small towel
- Phone and wallet
Best for: Quick gym sessions, day spa visits, overnight stays when packing light, personal item on flights alongside a larger carry-on.
Small (20-35L)
The sweet spot for gym bags and overnight trips. This size balances portability with practical capacity.
What it holds:
- Full gym outfit including shoes
- Towel (gym-sized)
- Toiletries kit
- Work/post-gym clothes
- Water bottle and snacks
- Electronics and chargers
OR for overnight travel:
- 1-2 complete outfits
- Sleepwear
- Toiletries
- One pair of additional shoes (packed flat)
- Minimal accessories
Best for: Daily gym visits, one-night trips, as a personal item for longer flights, day adventures.
For gym use, 25-30L is the most popular size range. It fits everything you need without tempting you to overpack. Larger gym bags often just accumulate more clutter.
Medium (35-50L)
The versatile travel range. Most carry-on compliant duffles fall within this category, making it ideal for frequent flyers and weekend warriors.
What it holds:
- 4-5 complete outfits
- 2-3 sets of underwear and socks per day
- Sleepwear and loungewear
- Full toiletry kit
- 1-2 additional pairs of shoes
- Light jacket or sweater
- Electronics, books, travel accessories
Best for: Weekend trips (2-4 nights), carry-on travel for up to a week (with efficient packing), short business trips, as the main bag for minimalist long-term travellers.
Australian airline considerations: A 40L duffle typically measures around 55 x 30 x 25cm — within most domestic carry-on limits. However, duffles can be squeezed into smaller overhead bins more easily than rigid luggage of the same volume.
Large (50-70L)
Stepping into checked baggage territory for air travel, but perfect for road trips, long holidays, or when you simply need more space.
What it holds:
- Week+ worth of clothing
- Multiple pairs of shoes
- Bulky items like jackets or sports equipment
- Full-sized toiletries
- Gifts or purchases
Best for: Week-long holidays, road trips where space isn't limited, checked luggage when flying, family travel where you're sharing a bag, sports trips with equipment needs.
Extra Large (70L+)
Expedition-grade sizes designed for extended travel or gear-heavy adventures. These are serious bags for serious trips.
What it holds:
- 2+ weeks of clothing
- Camping or outdoor gear
- Sports equipment
- Cold-weather layers
- Essentially everything you might need for an extended adventure
Best for: Expedition travel, extended outdoor adventures, group gear hauling, moving or relocating, sports team equipment.
Large duffles filled to capacity can exceed airline weight limits and become difficult to carry. Consider whether you can actually lift and manage a fully loaded 90L bag. For most people, two smaller bags are more practical than one massive one.
Activity-Based Recommendations
Daily Gym Use
Recommended: 25-35L
You need space for workout clothes, shoes, towel, toiletries, and post-gym attire. A 30L bag handles this perfectly with room for extras like resistance bands or a shaker bottle.
Weekend Getaway
Recommended: 35-45L
Two to three nights requires more than gym gear but less than a full suitcase. A 40L bag fits comfortably in car boots and aeroplane overheads while holding everything you need.
Domestic Carry-On Travel
Recommended: 35-45L
Match Australian airline dimension limits. A 40-45L duffle maximises capacity within carry-on constraints, letting you travel for up to a week without checking bags.
International Travel (Checked)
Recommended: 50-70L
When checking luggage, you have more freedom but still face weight limits (usually 23kg). A 60L bag offers excellent capacity without becoming unmanageable.
Outdoor Adventures
Recommended: 45-90L (varies by activity)
Camping, hiking, and water sports require more gear. Choose based on equipment needs — a kayaker might need 70L for dry bags and gear, while a road cyclist might manage with 45L.
Packing Efficiency Matters More Than Size
A skilled packer can fit a week's wardrobe into 35L while an inexperienced packer overflows at 50L. Before buying a larger bag to accommodate "more stuff," consider whether better packing technique would solve your problem.
Key efficiency strategies:
- Rolling clothes instead of folding saves 20-30% space
- Compression bags reduce bulky items dramatically
- Packing cubes organise and compress simultaneously
- Wearing bulky items (jacket, boots) instead of packing them
- Choosing versatile clothing that mixes and matches
See our air travel packing guide for detailed techniques.
When Size Categories Overlap
If you're between sizes, consider:
- Go smaller if: You want to force yourself to pack light, you value portability, or you're using the bag for carry-on only
- Go larger if: You tend to overpack and feel stressed when constrained, you're buying a single versatile bag for multiple purposes, or you frequently return with more than you left with (purchases, gifts)
Final Thoughts
The "right" size depends entirely on how you travel and what you carry. There's no universal answer — a minimalist traveller thrives with 35L while a gear-heavy photographer needs 70L for the same trip duration.
If you're unsure, start with a 40L bag. It's the most versatile size, handling everything from extended weekends to week-long trips, fitting carry-on requirements while offering substantial space. From there, experience will teach you whether you need more or less capacity for your specific lifestyle.
Use our interactive quiz to get personalised recommendations based on your intended use, or browse our product comparisons filtered by size category.