How do you measure luggage capacity

Recommendation: Prefer bags with a stated internal volume in litres or record internal dimensions (cm) and convert: length × width × height (cm) ÷ 1,000 = litres. Target ranges: cabin-style roll-aboards 35–45 L, larger checked-style trunks 60–100 L; choose a size that keeps packed weight below common airline limits (7–10 kg for carry-on, 23 kg for standard checked, 32 kg for oversized checked).

Step-by-step procedure: 1) Empty the case and lay it flat. 2) Record internal usable length, width and depth in centimetres (exclude wheel housings and retracted handles for internal volume). 3) Multiply L×W×H to get cubic centimetres; divide by 1,000 to obtain litres. Example: 55 × 40 × 20 cm = 44,000 cm³ = 44 L. For curved or tapered interiors approximate by measuring the largest rectangular block that fits inside.

Adjustments and practical coefficients: For hard-shell models subtract ~1–2 cm per side from external dimensions to estimate internal space; for fabric shells apply a packing-efficiency factor: dense items (shoes, electronics) use ~0.95, mixed clothing ~0.80–0.85. Zipper expansion of 3–5 cm increases volume by roughly (L×W×ΔH)/1,000 litres – e.g., 55×40×5 cm ≈ +11 L.

Airline rules and verification: Use external dimensions including wheels and handles when checking airline linear limits (common checked linear maximum = 158 cm; example: 80 + 50 + 28 = 158 cm). Carry-on cabin limits frequently listed as 55×40×20 cm (≈44 L) or by linear sum. Confirm permitted weight per piece (typical values: 7–10 kg cabin, 23 kg checked); leave a 10–20% margin on planned fill to avoid overage fees.

Quick checks before travel: Place typical items into the case and confirm zipper closure and final weight on a luggage scale; for online shopping compare stated litres to the L×W×H calculation and check whether listed figures are internal or external. If exact litres are critical, prefer models with manufacturer internal-volume specifications and test pack to validate real-world usable space.

Take external dimensions with a tape and calculate cubic volume in liters

Use a rigid tape with centimetre markings; record external length, width and depth to the nearest centimetre, including wheels, bumpers and stowed handles.

Procedure

Place the case on a flat surface so it rests naturally on its wheels. Take three straight-line readings: length = longest external edge, width = side-to-side at the widest point, depth = top-to-bottom at the deepest point. Record values in cm.

For rounded corners or curved shells, use the maximum straight-line dimensions (do not trace curves). For soft-sided shells press to the typical packed profile and note resulting sizes. For external pockets or detachable pouches, approximate each as a rectangular block (L×W×D) and add their volumes to the main body.

Conversion and example calculations

Use the formula: cubic litres = (L × W × D) / 1000, with L, W, D in centimetres. To convert from inches: multiply each inch value by 2.54 first; to convert cubic inches to litres multiply cubic inches by 0.016387.

Round litres to one decimal for inventory or to whole litres for quick comparisons. For carrier size limits use the external dimensions with handles stowed and wheels included; if in doubt, add 1–3% to account for fabric bulge and pockets.

Compartment-by-compartment assessment of usable interior volume for soft-sided bags

Calculate usable interior volume compartment-by-compartment, apply pocket-specific fill factors, then add net results for an accurate total.

• Tools: flexible cloth tape (150 cm, mm marks), pocket ruler, small objects for fill-testing, calculator or phone.
• Preparation: empty every pocket and open zips/gussets fully; flatten removable dividers to their installed position.
• Recording method:
  1. For each compartment record maximum internal length (L), width (W) and depth (D) along seams or at the point a typical item contacts the lining; use the tape to follow curves.
  2. For sleeves note maximum device thickness instead of full depth if padding compresses (record both uncompressed and typical compressed thickness).
  3. For expandable panels record dimensions with the panel deployed and with it stowed.

Shape-based volume rules and conversions

• Convert raw cubic centimetres to litres: (L × W × D) / 1000 = litres.
• Approximate irregular pockets by summing simple shapes:
  • Rectangular prism: L×W×D.
  • Half-cylinder (rounded top): (π × r² × L) / 2, where r = half the width.
  • Triangular wedge: (base × height × length) / 2.
• Apply realistic fill factors (multiply raw volume by factor):
  • Main soft compartment (clothes): 0.85 typical; range 0.75–0.90 depending on compression and lining stiffness.
  • Padded laptop/tablet sleeve: 0.90–0.98 (padding occupies most of raw space but accepts devices snugly).
  • Thin document/flat zip pockets: 0.20–0.40.
  • Stretch mesh pockets: 0.60–0.95 depending on elasticity.
  • Small organizer pockets (bottle holders, pen slots): use 0.10–0.30 per slot.
• Adjustments:
  • Compression straps in use: reduce usable by 5–10% from the computed total.
  • Internal rigid frames or thick padding: subtract 5–15% raw volume where structure blocks fill.
  • When gusseted panels unzip, add the deployed raw volume fully; when zipped, use stowed dimensions.

Worked example

1. Main compartment: 55 × 35 × 22 cm = 42,350 cm³ → 42.35 L raw. Apply 0.85 fill factor → 36.0 L usable.
2. Front pocket (flat): 30 × 25 × 3 cm = 2,250 cm³ → 2.25 L raw. Apply 0.30 → 0.68 L usable.
3. Laptop sleeve: 38 × 26 × 2 cm = 1,976 cm³ → 1.98 L raw. Apply 0.95 → 1.88 L usable.
4. Rounded external pocket approximated as rectangular (30×20×6=3,600) + half-cylinder top (r=10 cm, L=30 → 4,712 cm³/2 rule applied above) → combine and convert, then apply 0.70 fill factor.
5. Sum of usable volumes = Main + Front + Sleeve + External pocket = example total ≈ 38.6 L (after rounding and adjustments for straps/dividers).

Label each compartment with its computed usable litres and keep a short list (or photo with notes) inside the bag for rapid reference when packing or comparing models.

Use water displacement for irregular-shaped or highly flexible bags

Required materials

Large watertight tub with known internal volume or clear overflow trough (examples: 80–120 L plastic storage tub for backpacks; 150+ L for duffel/beanbag items), a graduated jug (minimum 10 mL resolution; 1,000 mL = 1 L), heavy-duty clear plastic liner or inflatable bladder to isolate inner cavity, waterproof clip or clamp, kitchen thermometer (optional), digital kitchen scale (optional, for mass-to-volume checks).

Recommended tolerances: tub volume accuracy ±0.5 L, graduated jug precision ±0.01 L for repeatable results. Use fresh water at ~20 °C for stable handling; record temperature if converting between mass and volume.

Procedure and calculations

Perform an overflow method: fill tub to a marked level that leaves room for full submersion but prevents splash; note initial water volume to nearest 0.1 L. Insert the item with a sealed inner liner (liner placed inside the opening and sealed with a clamp) so interior stays dry; submerge fully while compressing gently to expel trapped air until shape approximates a normally packed form. Collect all overflow into the graduated jug. Displaced volume (in liters) = volume collected in the jug. Example: collected 12.7 L → internal volume ≈ 12.7 L.

Alternative for open, very flexible goods: fit a heavy plastic liner inside, pour water into the liner until the shell is fully filled without bulging beyond natural shape, then pour liner contents into the graduated jug. Repeat filling until the shape matches intended packed firmness. Example calibration: repeat fill three times and average values; three samples 9.4 L, 9.6 L, 9.5 L → reported volume 9.5 L ±0.1 L.

Sources of error and mitigation: trapped air will under-report true interior volume – ensure air pathways are open during submersion or use a small vent tube. Excessive compression will under-report; mimic packing pressure by placing a 1–3 kg distributed weight if realistic for the item. Liner thickness reduces reported space by its internal thickness; select thin, taut liners and add liner volume correction if known (measure liner volume empty). Expected accuracy: 1–5% with careful technique; coarse setups may vary by 10%.

Conversions and quick references: 1 L = 1,000 cm³; 1 in³ = 0.016387 L. For mass-based checks, use water density at 20 °C (0.9982 g/mL): mass (g) ≈ volume (mL) × 0.9982. Record final value in liters and, if needed, in cubic centimetres for comparison with manufacturer specs.

Practical notes: dry the item and liner between trials to prevent contamination; avoid electrical equipment near the tub; dispose of used water responsibly. Report the averaged displaced volume and state the packing pressure simulated (e.g., “lightly compressed with 2 kg weight”) so the result matches intended use-case.

Convert cubic inches to liters and check against airline carry-on and checked size rules

Multiply cubic inches by 0.016387064 to get liters (L); multiply liters by 61.0237441 to get cubic inches (in³).

Quick calculator values: 1,000 in³ = 16.387 L; 2,772 in³ (22×14×9 in) ≈ 45.4 L; 3,000 in³ ≈ 49.2 L; 7,938 in³ (example checked suitcase 27×21×14 in) ≈ 130.0 L.

When an airline gives dimensions in centimetres, compute liters directly: (cm length × cm width × cm height) ÷ 1,000 = liters. Example: 55×40×20 cm → 44,000 cm³ → 44 L.

Typical thresholds to compare against: most legacy carriers accept carry-on near 22×14×9 in (≈45 L); many European limits are 55×40×20 cm (≈44 L); low-cost hand-bag limits may be as small as 40×20×25 cm (≈20 L). Checked-bag linear limit commonly listed as 62 in (158 cm) total; typical large checked cases fall in the 90–130 L range depending on proportions–convert actual in³ to L using the factor above to determine whether a specific bag fits airline rules.

If an airline publishes only a linear-sum limit (L+W+H), use the published linear dimensions for a direct fit check; if only volume or weight limits are published, convert in³↔L with the factors above. For unrelated appliance safety reading, see are swan fridge freezers safe.

Translate liters into practical loads: outfits, shoes and electronics per trip

Quick item-to-liter cheat sheet

Baseline estimates: T-shirt 0.8 L, long-sleeve shirt 1.0–1.2 L, underwear 0.25 L, socks 0.15 L, lightweight shorts 0.9 L, jeans 3.0 L, lightweight dress 1.6 L, light sweater/fleece 3.5 L, trainers/sneakers 7 L, sandals 2.5 L, hiking boots 11–13 L, toiletry kit (travel bottles + small pouch) 1.5–2.5 L, 13″ laptop + charger 2.5–3 L, 15″ laptop + charger 3.5–4 L, compact mirrorless camera + one lens 2–3 L, phone + charger + powerbank + cables 0.6–1 L, noise-cancelling headphones 1.5–2 L.

Packing recipes by trip length and bag size

Weekend city break (2–3 days): target 15–25 L. Example load: 2 T-shirts (1.6 L), 1 pair jeans (3 L) or 1 pair lightweight trousers (1.5 L), 3 underwear + 2 socks (~0.9 L), 1 pair sneakers (7 L) or sandals (2.5 L), phone + charger + small toiletry (1.5–2 L). Recommended: 20–25 L daypack or small carry-on. Musicians needing cables, pedals or a compact pedalboard should look at a 25–30 L pack such as the best backpack for musicians.

Short work trip (3–4 days): target 25–35 L. Example load: 3 shirts (2.4–3.6 L), 2 underwear + socks (0.9 L), 1 pair trousers (2.5–3 L), 1 pair shoes (7 L), 13″ laptop + charger (3 L), toiletry kit and a small folder/notebook (2 L). Recommended: 25–30 L backpack or a 10–15 L messenger for minimal carry; educators or commuters who carry papers and a laptop should consider the best messenger bag for female teacher in the 12–16 L range.

One-week trip (5–7 days): target 35–45 L. Example load: 5 tops (4–6 L), 2 bottoms (5–6.5 L), 5 underwear/socks (1.5 L), 1 sweater (3.5 L), 1–2 pairs shoes (7–14 L depending on type), laptop and camera kit (4–6 L), toiletry kit (2–3 L). Recommended: 35–45 L carry or checked bag hybrid; use one shoe pair on feet to save internal liters.

Extended travel (8–14 days): target 55–85 L. Example load: mix of 8–10 tops (6.4–10 L), 3–4 bottoms (8–12 L), 2 sweaters (7 L), 2–3 pairs shoes (14–22 L), full electronics kit including laptop, camera, chargers and accessories (6–9 L), larger toiletry kit and travel adapter (3–4 L). Recommended: 60–80 L checked suitcase or large duffel; compress bulky outerwear with vacuum or compression bags to reclaim 20–40% of listed liters.

Packing technique to convert listed liters into usable outfit counts: roll T-shirts to reduce their effective liter by ~20–30%, use compression sacks for sweaters and jackets to reclaim 30–50% of their liters, reserve one internal 1–2 L pocket for chargers/cables to avoid tangled bulk, and place heavy electronics centrally and flat for best space efficiency and protection. For musicians carrying fragile gear, choose padded compartments and modular inserts described on the best backpack for musicians page; for teacher-style daily loads prioritize organizer pockets and a dedicated laptop sleeve as shown on the best messenger bag for female teacher review.