Michael Turner
Pick 30–40 L when you need a single rucksack that fits most airline cabin-size allowances while still holding a 15″ laptop, one change of clothes, basic toiletries and a light pair of shoes. If the item must slide under the seat, aim for ≤20 L; if you plan to stow it above the seat, 30–40 L gives usable space without exceeding typical dimensional checks.
Concrete airline references: Ryanair small personal 40×20×25 cm (rectangular 20 L; typical soft pack usable ~12–18 L); Ryanair priority/large cabin 55×40×20 cm (rectangular 44 L; realistic pack capacity ~30–40 L, common weight limit 10 kg). easyJet standard 56×45×25 cm (rectangular 63 L; soft packs accepted usually in the 35–45 L range). American Airlines / United / Delta 22×14×9 in (56×36×23 cm ≈ 46 L raw; comfortable pack size ~30–40 L). Low-cost carriers may restrict to a single small item, so carry a 15–20 L daypack to avoid fees.
Packed-volume tips: use a pack with external compression straps and a padded laptop sleeve, measure packed dimensions with clothes and shoes inside, and keep weight under 8–10 kg when airlines enforce limits. Calculate rectangular volume (L×W×H in cm ÷ 1000) as a starting point, then reduce by 20–40% to estimate realistic usable litres for soft-sided designs.
Quick purchase checklist: confirm the carrier’s exact linear dimensions before buying; prefer soft-sided rucksacks that can be squashed into a sizer; choose a model with adjustable straps and separate tech pocket; verify the empty-and-packed measurements at home on a luggage scale and with a tape measure to avoid gate fees.
Recommended L volume – cabin luggage limits
Choose a 30–40 L daypack as the default cabin-sized rucksack: 30 L fits minimalist packing and personal-item limits, 35–40 L accommodates a 2–5 night itinerary when compression straps reduce bulk to typical airline dimensions.
Dimensions guidance
Underseat personal item: 12–20 L (approx 40 x 30 x 15 cm) – fits a 13–14″ laptop, toiletry pouch, and one outfit. Overhead-bin target: 35–45 L with external dimensions near 55–56 x 35–36 x 20–23 cm; most carriers accept that footprint. Typical loaded weight range: 6–10 kg; low-cost airlines may impose stricter kg limits or separate personal-item policies.
Packing strategy and small-item choices
Use two packing cubes (clothes), a slim shoe sac, and a dedicated toiletry pouch; place dense items close to the spine and light layers at the top. Store liquids in 100 ml bottles inside a clear pouch for security checks. Limit footwear to 1–2 pairs and keep electronics in an easy-access pocket to speed inspections. Snack planning: consult which nut butter has the most protein to select compact, high-protein options that save space and weight.
Before departure measure the chosen bag fully packed (height × width × depth) and compare with the airline’s published cabin and personal-item dimensions; if a scale is available, test a loaded weight to avoid gate fees.
Convert external dimensions (cm/in) into litres to check cabin allowance
Measure external length × width × depth in centimetres, multiply those three numbers and divide by 1000 to obtain litres.
If original measurements are in inches, multiply each inch value by 2.54 to get centimetres (1 in = 2.54 cm).
Volume (L) = (L_cm × W_cm × D_cm) ÷ 1000. Example: 55 × 40 × 20 cm = 44,000 cm³ → 44 L.
Estimate usable internal volume: soft/compressible designs multiply external litres by 0.85; semi-structured designs multiply by 0.75; framed or rigid designs multiply by 0.60. Example: external 44 L × 0.85 = 37.4 L usable.
Include wheels, fixed handles and external pockets when measuring; tighten compression straps and measure at the widest points. Retract telescopic handles as many carriers require; if policy is unclear, record both retracted and extended sizes and use the larger total dimension when checking allowance.
Cylindrical item formula: V(cm³) = π × (radius_cm)² × height_cm. Example: 30 cm diameter × 50 cm high → radius 15 cm → V = 3.1416 × 225 × 50 = 35,343 cm³ → 35.3 L.
Most carriers limit linear dimensions (L + W + D). Example common limit 55 + 40 + 20 = 115 cm total. When comparing measured litres against a stated litre limit, round up to the next whole litre to avoid underestimation.
Manufacturer-rated capacity typically reflects internal packing volume; expect external measured litres to be about 5–15% larger due to shell thickness and external fittings. Use external measurement rounded up and cross-check linear dimension sums against carrier size rules.
Quick checklist: measure in cm; convert inches with 2.54; include wheels and straps; apply packing coefficient per bag type; round up litres; verify L+W+D against carrier maximum.
Exact liter ranges accepted by major carriers – US, EU, Asian examples
Recommendation: target a pack volume of 35–45 L to meet the most common US and Asian cabin-bag limits; expect European allowances to range from about 20 L (small under-seat) up to roughly 63 L (larger permitted cabin item on some fares).
Below are concrete airline examples with published maximum external dimensions converted to approximate internal volume (litres). All volumes are approximate; airlines enforce external linear dimensions (L+W+H) and sometimes weight.
| Region | Airline / Product | Max external dims (cm) | Approx. max volume (L) | Notes |
|---|---|---|---|---|
| US | American Airlines | 56 x 36 x 23 | ≈46 L | Standard cabin allowance; no published weight limit but must stow in overhead or under seat |
| US | Delta Air Lines | 56 x 36 x 23 | ≈46 L | Typical US legacy-size rule |
| US | United Airlines | 56 x 36 x 23 | ≈46 L | Same dimensional ceiling as other major US carriers |
| US | Southwest | 61 x 41 x 25 | ≈63 L | Larger allowed external size compared to typical US carriers |
| EU | Ryanair (Priority) | 55 x 40 x 20 | ≈44 L | Priority permits a larger cabin item; non-priority free small bag: 40 x 20 x 25 → ≈20 L |
| EU | easyJet (standard) | 45 x 36 x 20 | ≈32 L | Higher-tier fares allow a bigger cabin piece (example sizes up to ~56 x 45 x 25 → ≈63 L) |
| EU | British Airways | 56 x 45 x 25 | ≈63 L | One cabin bag plus one personal item; larger dimensional ceiling than many carriers |
| EU | Lufthansa | 55 x 40 x 23 | ≈51 L | Common European standard with occasional weight guidance |
| EU | Air France / KLM | 55 x 35 x 25 | ≈48 L | Typical Schengen/ intra-Europe allowance |
| Asia | Singapore Airlines | 55 x 40 x 20 | ≈44 L | Common cabin limit; published weight limit often 7 kg on some fares |
| Asia | Cathay Pacific | 56 x 36 x 23 | ≈46 L | Typical premium-carrier dims; weight limit may apply (e.g., 7–10 kg) |
| Asia | ANA (All Nippon) | 55 x 40 x 25 | ≈55 L | Generous depth compared with some regional peers |
| Asia | Japan Airlines | 55 x 40 x 25 | ≈55 L | Often combined with a weight cap on certain ticket types |
| Asia | Korean Air | 55 x 40 x 20 | ≈44 L | Standard 55 cm height is common across Asian carriers |
| Asia | EVA Air | 56 x 36 x 23 | ≈46 L | Typical premium-regional allowance |
Practical rule: choose a pack whose external measured dimensions (including wheels and handles) fit the specific airline line in the table and stay within the listed litre estimate; check any airline weight cap (often 7–10 kg on several Asian carriers) prior to travel.
Measure your pack: tape-measure steps and simple volume formula
Recommendation: Measure external length, width and depth at the fullest points; multiply (cm × cm × cm) ÷ 1000 to obtain litres and include pockets, straps and protrusions.
1. Place the pack upright on a flat surface in the typical packed orientation. Measure length (top-to-bottom) along the centreline, width (side-to-side) at the widest point, depth (front-to-back) at the bulkiest point.
2. If a roll-top or compressible collar exists, measure with the closure set to the height expected during transit; if compression straps will be used, tighten them and measure while secured.
3. Tapered shapes: take two depth readings (maximum and minimum), compute average depth = (max + min) ÷ 2, then use the rectangular formula with that average depth.
4. Irregular shapes: split the item into stacked rectangular blocks or simple shapes (rectangular prisms, cylinders), measure each segment, convert each segment to litres, then sum segment volumes.
Rectangular prism formula: volume (L) = (L cm × W cm × H cm) ÷ 1000.
Cylindrical approximate: volume (L) = (π × r² × h) ÷ 1000, where r and h are in centimetres.
Example – rectangular: 50 × 30 × 20 cm → (50 × 30 × 20) ÷ 1000 = 30 L.
Example – tapered: height 50 cm, width 30 cm, depth max 25 cm, depth min 10 cm → avg depth 17.5 cm → (50 × 30 × 17.5) ÷ 1000 = 26.25 L.
Example – cylinder: diameter 28 cm (r = 14 cm), length 40 cm → π × 14² × 40 ≈ 24,630 cm³ ÷ 1000 ≈ 24.6 L.
Convert inches: multiply inches by 2.54 to obtain centimetres, then apply formulas above.
Add a safety margin of 5–10% to the final litre figure to cover bulging, packed contents and measurement error; record both empty (compressed) and packed (expanded) volumes when planning.
Packing to meet strict overhead limits: arrange a 30–45 L pack to pass gate checks
Target compressed volume: 30–40 L; target weight ≤10 kg; maximum external depth ≤23 cm; aim to fit a 56×36×23 cm sizer with all pockets flattened.
Load order and placement
- Core: place dense items (camera bodies, compact shoes in slim shoe bags) along the spine to keep profile narrow and stable.
- Surround the core with rolled clothing inside a single compression cube to remove dead space and shave height.
- Top pocket: 1 L clear liquids pouch with containers ≤100 mL each; keep this pouch visible for quick inspection.
- Quick-access sleeve: laptop or tablet in a thin protective sleeve; position at the top so it can be removed without emptying the main compartment.
- External straps and daisy chains: tuck into side pockets or clip them to internal webbing; stowed hardware must not protrude beyond the sizer envelope.
Volume-reduction tactics that pass gate inspection
- Wear the bulkiest items onboard (jacket, boots, heavy sweater) and pack compressible substitutes to reduce packed bulk.
- Use 100 mL decants and a single 1 L clear pouch; swap liquid toiletries to solids (soap, shampoo bars) where possible.
- Prefer single-layer packing cubes over multiple nested organizers; alternate rolled and flat garments to avoid hard corners.
- Move shoes to the bottom in slim shoe bags, then squeeze with side compression straps to flatten the base.
- Keep spare lithium cells and large power banks in an external pocket so staff can inspect without opening the main compartment.
- If the pack sits too tall in the sizer, unzip expansion panels, compress straps, remove shoes or outer layer, then re-present it to the agent.
When choosing a model with low-profile compression and removable hipbelt, compare options at best luggage for travel to africa.
When a 35–45 L pack will be gate-checked and concrete actions to avoid it
If external dimensions exceed ~22 x 14 x 9 in (56 x 36 x 23 cm) or the bag looks rigid and overstuffed at boarding, expect gate-checking even at 35–45 L; any depth over ~9–10 in (23–25 cm) or bulky top flaps are common triggers.
Immediate physical fixes: (1) compress: move items into packing cubes or a compression sack to shave 2–4 in (5–10 cm) of depth; vacuum-style compression can reduce volume by up to 30–40%. (2) strip structure: remove or fold outboard frames, unclip and tuck hip belts and sternum straps into an internal pocket so no loose straps add to measured size. (3) flatten electronics: put laptop/tablet into a slim sleeve, then place against the rear panel to decrease protrusion.
Repacking swaps that save space: transfer shoes and bulky toiletry containers into a separate underseat personal item or a soft tote; move a jacket to wear onboard; redistribute heavy items into pockets of a coat or into a small duffel that fits under the seat. Keep liquids under 100 ml in a clear bag inside the item you plan to keep with you.
Hardware and accessorizing: replace a rigid top lid with a removable flap or compress it; use external compression straps to reduce profile; fold external pockets flat or empty them. To free overhead bin room, attach the pack to a wheeled suitcase handle with a J-style hanger – see best luggage j hook – which keeps it compact and easier to lift into a bin.
Boarding and policy tactics: purchase or use priority boarding to secure early bin space; choose a seat toward the front with later groups more likely to have full bins behind them. If gate staff still request gate-check, remove passports, medication, valuables, and a change of clothes first; place electronics in a padded sleeve and put that into a personal item you keep with you.
If avoiding gate-check is not possible: check at the ticket counter instead of the gate to ensure a baggage receipt and better handling; add a lightweight protective cover or a marked tag, and photograph the bag front and contents for claims if damage occurs.
